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1. Data representation Flashcards

1
Q

Define a bit

A

The basic computing element that is either 0 or 1

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2
Q

Define the binary number system

A

A number system based on 2 and can only use values 0 and 1

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3
Q

Define an error code

A

It is an error message generated by the computer

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4
Q

Define a MAC address

A

It is an address (given in hexadecimal) that uniquely identifies a device on the internet in the form of NN-NN-NN-DD-DD-DD

(NN-NN-NN is the manufacturer code)

(DD-DD-DD is the device code)

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5
Q

Define an IP address

A

It is an address that uniquely identifies each device connected to a network identifying their location.

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6
Q

Define HTML

A

It is used to design and write webpages

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7
Q

Define an overflow error

A

The result of doing a calculation that produces a value that is too big for the computers allocated word size

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8
Q

Define logical shift

A

An operation that shifts bits to the left or right in a register.

(Any bits shifted out of the register are replaced with zeroes)

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9
Q

Define the two’s complement

A

A method of representing of negative numbers in binary

(When applied to an 8-bit system, the left most bit is given the value -128

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10
Q

What is an ASCII code

A

A character set for all the characters on a standard keyboard and control codes.

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11
Q

Define a character set

A

a list of characters that have been defined by computer hardware and software.

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12
Q

Define an Unicode

A

a character set which represents all the languages of the world

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13
Q

Define a sampling resolution

A

the number of bits used to represent sound amplitude in digital sound recording

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14
Q

Define what is bit depth

A

the number of bits used to represent the smallest unit in a sound file

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15
Q

Define what is color depth

A

the number of bits used to represent the colours of a pixel

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16
Q

Define sampling rate

A

the number of sound samples taken per second in digital sound recording

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17
Q

Define bitmap image

A

an image made up of pixels

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18
Q

Define pixel

A

the smallest element used to make up an image on a display

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19
Q

Define image resolution

A

the number of pixels in the X–Y direction of an image,

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20
Q

Define pixelated image

A

this is the result of zooming into a bitmap image; on zooming out the pixel density can be diminished to such a degree that the actual pixels themselves can be seen

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21
Q

Define pixel density

A

number of pixels per square inch

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22
Q

Define compression

A

reduction of the size of a file by removing repeated or redundant pieces of data;

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23
Q

Define bandwidth

A

the maximum rate of transfer of data across a network, measured in kilobits per second (kbps) or megabits per second (Mbps)

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24
Q

Define lossy file compression

A

a file compression method in which parts of the original file cannot be recovered during the decompression process

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25
Define lossless file compression
A file compression method that allows the original file to be fully restored during the decompression process, for example, run length encoding (RLE)
26
Define audio compression
a method used to reduce the size of a sound file using perceptual music shaping
27
Define MP3
a lossy file compression method used for music files
28
Define MP4
a lossy file compression method used for multimedia files
29
Define JPEG
; a form of lossy file compression used with image files which relies on the inability of the human eye to distinguish certain colour changes and hues
30
Define RLE
a lossless file compression technique used to reduce the size of text and photo files in particular
31
How do you calculate The file size of an image
image resolution (in pixels) × colour depth (in bits)
32
How do you calculate The size of a mono sound file
sample rate (in Hz) × sample resolution (in bits) × length of sample (in seconds)
33
Why is file compression necessary
» to save storage space on devices such as the hard disk drive/solid state drive » to reduce the time taken to stream a music or video file » to reduce the time taken to upload, download or transfer a file across a network » the download/upload process uses up network bandwidth » reduced file size also reduces costs.
34
Define a data packet
a small part of a message/data that is transmitted over a network
35
Define a data packet
a small part of a message/data that is transmitted over a network
36
What is the building block of all computers and why
What do switches in a computer do and what is another name for themBinary number system, because it is only made up of 0’s and 1’s. Computers contain millions of tiny switches that must be in either the ON or OFF position. These positions can be represented by the binary number system. 1=ON(high) 0=OFF(low)
37
What do switches in a computer do and what is another name for them
Make use of logic gates and store and process data Microtransistors
38
What does binary allow computers to do
Carry out calculations
39
What is a bit
A basic computing element that is either a 0 or 1, comes from BInary digiT
40
What is the binary number system
A number system based on 2, and only contains 0’s and 1’s
41
What is the denary system also called
A base 10 number system
42
What are the uses of the hexadecimal system
Error codes Mac address IPv6 adress HTML colour codes
43
What are error codes
They are codes that are usually automatically generated, and refer to the memory location of the error
44
What does the MAC address stand for
Media Access Control address
45
What does NIC stand for
Network interface card
46
What is a MAC address
A number which uniquely identifies a device on a network, it refers to the NIC.
47
Why are MAC addresses rarely changed
So that a particular device can always be identified no matter where it is
48
What does the NN-NN-NN in a MAC address identify What does the DD-DD-DD in a MAC address identify
The number of the manufacturer The device serial number
49
What do IP addresses stand for
Internet protocol addresses
50
What is the difference between an IPv4 and an IPv6
32 vs 128 bit number. IPv6 uses a colon instead of a decimal point
51
What does HTML colour codes stand for
Hyper text markup language colour codes
52
Why is the maximum denary value of an 8-bit binary number
255 (2^8-1)
53
What is it called when there is more than 8 bits generated after calculations and what does it mean
Over flow The number is too big to be stored in the computer using 8 bits A bigger register needs to be used
54
What is an overflow error
The result of carrying out a calculation where the result is too big for the computers word size.
55
What is hexadecimal
A number system based on 16, goes from 0-9 and then A-F
56
What is HTML
It is a mark-up (NOT PROGRAMMING) language used when writing and developing web pages It uses tags<> Often represents colours of text on screen
57
What is a logical shift
An operation that shifts buts left/right in a register and replaces shifted bits with 0 Left shift= multiply binary number by 2 Right shift=divide binary number by 2
58
What is the left most bit reffered to as
The most significant bit
59
What does ASCII code stand for and what is it What was it originally used for
American Code for Information Interchange It is a set of characters for each character on a standard keyboard/control code. Communication and computer systems
60
What is a character set
A set of characters that have been defined by computers hardware and software. It is used so that the computer can understand human characters.
61
What does the standard ASCII code character set consist of and what is it used for
7-bit codes(0-127 in denary/00to 7F in hex) Represent the letters numbers and characters found on a standard keyboard together with 32 control codes(0-31 denary, 00 to 19 hex)
62
What does ASCII vs unicode use to represent a character
1 vs 4 bytes
63
What were the goals of unicode (5)
To have uniform code Unambiguous code Reserve part of the code for private use Universal standard More efficient coding system
64
What is unicode
Character set that represents the languages of the world (first 128 are the same as ASCII)
65
What does the aplitude of a wave specify
The loudness of the sound
66
What is analouge data
Data that varies continuously
67
How do computers store sound wave data
They convert it from anolouge to digital using an ADC, sampling the amplitude at regular intervals. The amplitude cannot be precicely measured so approximate values are stored.
68
How could you get a more accurately sampled sound
By increasing the sampling resolution(bit depth)
69
What is sampling resolution
Also known as bit depth The number of bits used to represent sound amplitude in a digital recording
70
What is bit depth
The number of bits used to represent the smallest unit in a sound file
71
What is the sampling rate
The number of sound samples taken per second Measured in hertz where 1 herts means one sample per second
72
How is sampling used to record a clip (3)
The amplitude is first determined at set time intervals An approximate representation of the wave is produced Each sample is then encoded to a series of binary digits
73
What are the advantages of a higher sample rate/larger resolution
Larger dynamic range Less sound distortion Better sound quality
74
What are the disadvantages of a higher sample rate/larger resolution
Produces larger file size Takes longer to transmit/download Requires a greater processing power
75
What is a bitmap image
An image made up of pixels
76
What is colour depth
The number of bits used to represent the colours of a pixel
77
What is an image made up of
A two-dimentional matrix of pixels
78
What bit depth do modern computers have
24 bit depth
79
What is image resolution
The number of pixels that make up an image
80
Explain the drawbacks of high resolution images
They increase file sizes, which impacts how many images can be stored on the eg. Hardrive. It takes longer to download and transfer the images.
81
what is pixel density
The number of pixels per square inch
82
How big is a byte
8 bits
83
How big is a nibble
4 bytes
84
What is the largest memory size metioned in the textbook
Exabyte X10^18
85
What is a more accurate way of measuring memory sizes, and what should be measured using this
IEC memory size system International electronical commision RAM and ROM
86
Why would data need to be compressed
Storage Time taken to stream Reduce file size=reduce costs Reduce time to download/transmit Reduce bandwidth usage
87
What is bandwidth
Where maximum rate of data transfer accross a network measured in kbps or mbps
88
What is lossy file compression Eg.
A compression process that eliminates unneccesary date and some detail which cannot be recovered during the decompression process JPG MP3 MP4
89
How does lossy file compression affect MP3 (2)
It removes sounds out of the human hearing range If there are 2 sounds at the same time, one is removed
90
What is audio compression
A method used to reduce the size ofa sound file using perceptual music shaping
91
What is the difference between MP3 and MP4 files
MP3 is for music MP4 allows multimedia storage.
92
What is the JPEG file reduction process based on
Human eyes dont detect differences in colour as well as they do differences in brightness By separating pixel colour from brightness, images can be split into 8x8 pixel blocks which allows information to be easily discarded with minimal quality loss
93
When should lossless file compression be used
When comressing large/complex spreadsheets or downloading a large computer application
94
What is RLE and what does it do
Run-length encoding Form of lossless file compression Reduces size of a string of adjacent,identicsl data This string is then encoded into 2 values, the first being the number of identical items in the run, the second the code of the data (eg. ASCII) Only effective if there are long runs of repeated bits
95
Order and power of storage (bits)
2^1 bits, 2^2 nibbles, 2^3 bytes, 2^10 KB, 2^20 MB, 2^30 GB, 2^40 TB, 2^50PB
96
Storage for 1 ASCII character
1 byte
97
Storage for 1 UNICODE character
2 bytes
98
Hexadecimal base, characters and uses
Base 16, 0-9 then A-F, MAC Addresses/Html colour coding and computer error messages, IPV6 messages
99
How is data stored on a computer
In binary using 1s and 0s, on or off
100
What is a bitmap image
Bitmap (raster) images are comprised of small picture elements called pixels. Bitmaps blur when enlarged
101
What is a vector image
Vector images use mathematical expressions to describe how the image is created and do not blur when enlarged
102
JPG or JPEG images
JPG or JPEG is a type of bitmap image that has been compressed using lossy compression. When the image is enlarged it appears blurry.
103
Calculating bitmap file size
pixels down x pixels across x bit depth divide answer by 8 to give in bytes divide by 1024 if more than to give in KB and so on till PB
104
Sound stored on a computer
Humans hear sound as analogue data that varies over time though computers work with digital data. Computers sample the sound at difference time intervals to best recreate it.
105
Sound sample rate
The more samples per time interval the better the quality of sound
106
Sound file size calculation
frequency (sample rate/hertz) x bit depth x length x channels channels: stereo is 2 5.1 is 6 7.1 is 8
107
Lossy compression of sound file
In an MP3 file lossy compression works by removing frequencies humans can’t hear well and/or at all
108
MIDI files
MIDI files don’t contain music or sounds, they contain a list of commands that instruct a device on what sound to produce, how loud, what frequency and for how long.
109
Video file storage
MP4 files allow for multimedia, sound and picture
110
Uses of lossy compression
audio, video, images
111
Lossless compression uses
text
112
Binary systems
Computer uses binary. Has transistors which have 1s and 0s which are located in the integrated circuits.
113
Hexadecimal uses
Memory dumps Represent colour in HTML MAC Addresses URL Assembly language IPv6 Addresses Locations in memory
114
MAC Address structure composed of
NN-NN-NN-DD-DD-DD First part is the organisationally unique identifier (OUI) or the manufacturer ID Next is universally administered address (UAA) serial number
115
Describe MIDI File
Musical Instrument Digital Interface Stores a set of notes Does not store actual sounds Data in file recorded using digital instruments Sends file to audio synthesiser to play note Specifies when each note plays and stops, duration, tempo, instrument type Individual notes can be edited
116
Describe JPEG
Joint photographic experts group Standard format for storing lossy compression image Maintain decent img quality File size = pixels * primary Color’s
117
Describe MP3
Format for digital audio Actual recording of the sound Is a lossy compression format Recorded using microphone
118
Describe MP4
It can store multimedia Music, videos, text, photos Format of lossy compression
119
Describe Parity Check and its limitations
Method of data transmission System could use odd or even parity Odd/Even parity is decided and parity bit is added at the end When receiver gets data a check is performed Bits are counted If incorrect data sent repeatedly till server times out Limitations: Transposition error When bits still add up to odd/even number Even number of incorrect bits
120
Describe ARQ
Transmitter sends data in packets When received it is checked for errors If no errors, sends an acknowledgment If no acknowledgment received, it sends it repeatedly Till server times out
121
Describe check digit
Data is input with check digit Calculation performed on inputted data Calculated digit is then compared to a stores value If it matches, data entered is correct If no match, data entered is incorrect
122
Describe check sum
Transmitter sums up total group of data before transmission Data is sent along with the sum Receiver works out sum and compares to stored value from transmitter Data should match meaning it’s correct If no match data entered is incorrect
123
Memory ascending order
Small - Large Bit Nibble = 4 bits Byte = 8 bits Kilobyte = 1000 bytes Megabyte = 1000 kilobytes Gigabyte = 1000 megabytes Terabyte - 1000 gigabytes
124
Describe Lossy compression
A compression algorithm used Data will be lost permanently Reduce colour depth Reduce number of pixels Reduce sample rate Use perceptual music shaping (removes inaudible sounds)
125
Describe Lossless compression
Compression algorithm No data will be removed permanently For example an RLE algorithm may be used Repeated patterns are identified and indexed Sometimes replaced
126
Describe Bitmap img
Stores position and colour of every pixel Very detailed images used for photos Makes them large files If compression resolution decreased Uses .bmp file
127
Describe Vector img
Mathematically constructed image Uses math formulas to draw shapes and lines Results in small file size Uses .svg file Good for cartoons unaffected by pixelation
128
Why is Lossy better than Lossless
− Lossy decreases the file size more − Take up less storage space on webserver/users' computer − Quicker to upload/download − May not need to be high quality − Website will load faster for users − Less lag/buffering when watching − Takes up less bandwidth to download/upload − Uses less data allowance
129
Why is Lossless better than Lossy
− Image if compressed does not become pixelated − User has the option retain all original data − Can restore the compressed image into original − Also reduces file size to an extent
130
uses of binary system (3)
ASCII value unicode value instruction
131
memory measurements from smallest to largest (5)
1KB 1MB 1GB 1TB 1PB
132
advantages of using hexadecimal (5)
easier to understand easier to debug shorter so takes up less space faster to enter than binary conversion to binary is easier than from denary
133
uses of hexadecimal numbers (3)
MAC address HTML colours error messages
134
problems with shifting bits (3)
may run out of places at the end of the register end bit may be lost may result in loss of precision
135
what does HTML stand for
hyper text markup language
136
structure of HTML
structure used for layout in HTML doc, presentation and structure often kept separate HTML tag used for structure
137
URL (composed of 3 parts)
protocol filename webserver name
138
presentation of HTML
presentation used for colour/style in HTML doc, presentation and structure often kept separate CSS linked to the HTML used for presentation
139
what does MAC address stand for
Media access code
140
explain what is meant by a MAC address (6)
hardware address unique num associated w device LAA UAA first 6/8 digit = manufacturer code last 6/8 digit = serial num of device
141
What is the denary system?
Number system based on the number 10
142
What is the binary system?
Number system based on the number 2
143
What is the hexadecimal system?
Number system based on the number 6 Used for memory dumps, HTML, MAC addresses, web addresses and assembly code/machine code
144
How do you convert from binary to denary?
Add the powers above the binary number, add up the binary numbers where the 1s appear
145
How do you convert from denary to binary?
Under powers, add 1s from right to left if it can add to the number
146
How do you convert from memory sizes?
add / divide by 1024
147
How do you convert from binary to hexadecimal?
convert each group of 4 binary digits to a hex value
148
How do you convert hexadecimal numbers to binary?
convert each letter/number into 4-bit binary
149
How do you convert hexadecimal numbers to denary?
Remember the place values and then multiply the hex number by this
150
How do you convert denary numbers into hexadecimal numbers?
convert from denary to binary to hexadecimal
151
How is hexadecimal used for memory dumps?
allows the contents of the memory to be seen by the writer when developing new software enabling errors to be detected also used in diagnostics when a computer malfunction (hex used as it is easier to use than a long string of binary values)
152
What is HTML used for?
hypertext markup language used for when writing and developing web pages (uses tags)
153
What is MAC addresses used for?
to uniquely identify a device on the internet (can be UAA or LAA) first 6 digits for manufacturer code
154
How is hexadecimal used for web addresses?
ASCII codes can replace the URL (which are hex values)
155
How is hexadecimal used for assembly code / machine code?
makes it easier, faster and less error-prone in writing the code in binary
156
What are the Number Systems and their Bases?
Binary, Base 2 Denary, Base 10 Hexademical, Base 16
157
What is Binary?
Binary is a base 2 number system, having the digits 0 and 1 - which represent true and false, as well as voltage levels.
158
What is a bit?
A bit is the fundamental unit, 0 or 1.
159
What is the hierarchy of units in binary?
Bit → 1/0 Nibble → 4 Bits Byte → 8 Bits. Kibibytes → 1024 Bytes Mebibyte → 1024 Kibibytes Gibibyte → 1024 Mebibytes Tebibyte → 1024 Gibibytes Pebibyte → 1024 Tebibytes
160
What are the titles for the most left bit and the most right bit?
Most Left → Most Significant Bit Most Right → Least Significant Bit
161
What is Signed Binary?
Signed Binary are binary values of positive and negative, containing 2 variables of Sign and Magnitude. Signed binary has a Sign Bit, which is the MSB, at 1 it is negative, and at 0 it is positive. It cannot be used to processing zeroes, because zero cannot be positive or negative.
162
What are the possible textual representations?
ASCII Unicode
163
What is ASCII?
ASCII contains characters encoded with character sets → codes assigned to a character. Originally only 7 bits long, but extended to 8 to contain 256 characters.
164
What is Unicode?
Unicode was created due to ASCII’s inability to represent all possible characters. ASCII is a subset of Unicode, Unicode uses 16 bits, having codes for 120 000 characters.
165
What are encoding tables?
Character codes are sequential, so it is in ascending order. To find the code for another character, simply add to where a previous one is.
166
What is a pixel?
The smallest distinguishable feature.
167
How are images represented in binary?
Bitmaps, images are stored as an array of individual pixels.
168
How do you calculate an image’s size?
Pixel Width x Height
169
What is the resolution of an image?
It is the detail that an image holds, aka pixels per inch.
170
How is an image converted from analogue to digital?
A grid is placed over the image An average colour is found for each pixel and assigned a binary value Each pixel is represented by multiple bits, one combination a shade The number of bits in a pixel is called the colour/bit depth.
171
What affects an image’s size?
Increasing Resolution; Increasing Colour Depth Size = Pixel Size x Colour Depth (in bits)
172
What is Metadata?
It is data about data, for example it allows the image to be displayed properly as well as other unneeded data: File name; format; colour depth; resolution; camera details
173
What is the difference between analogue and digital data?
Analogue signals are continuous, represented by waves. Digital data is discrete, falling between defined ranges and taking only certain values. Computers require digital data, as it cannot read analogue signals.
174
What is a sampling frequency?
It is the number of samples obtained over second, measured in hertz. The greater the sampling frequency, the better quality but the larger file.
175
How is sound digitized?
Several samples should be taken at regular intervals, with a binary value given to each reading
176
What is a sample size?
It is the bit depth
177
What is the bit rate?
It is the number of bits used per second Bit rate = Sampling Frequency x Sample Size
178
How is a sound file size calculated?
It is the Sampling Frequency x Sample Size x Time
179
What is Compression and the Two Types of it?
Compression is the reduction of file size without losing important information. Lossy Lossless
180
What is Lossy Compression?
Lossy compression is a means of compression in which data is removed and lost forever. Some quality can be lost. E.g JPEG, MP3, MP4
181
What is Lossless Compression?
No data is removed here - it is maintained, but it is rearranged, for example using Run Length Encoding. Repeated data is replaced with frequency The more data the more the file can be compressed Can be restored fully
182
What is Encryption?
It is the process of making data secret so only authorised viewers can decrypt and read the data. It doesn’t prevent interception, it simply stops it from being understood.
183
What is the simplest process of Encryption?
Plaintext → Ciphertext → Message Sent → Message Received → Message Decrypted
184
Why is Encription Required?
It is needed to protect data, especially important ones Bank information, government details, identity information
185
What are the uses of hexadecimal
Memory dumps (B 5 A 4 1 A F C) Html color code (#FF 00 00 - red) Mac address (00-1C-B3-4F-25-FE) Web address Assembly language Error messages Locations in memory
186
Reasons for using hexadecimal
Easier for humans to read/ write/understand Easier to remember for humans easier to debug Fewer errors made Shorter way to represent data takes up less space on screen
187
Reasons to use binary
Computer uses logic circuits These can only process 1s and 0s
188
Describe html presentation
formatting/style Separate file/CSS used E.g background color Color applied to text Font style
189
Describe html structure
Layout of webpage Uses tags to define it Eg where paragraph is placed Where images is placed
190
How many GiB in a TiB?
1024 GiB
191
How many MiB in a GiB?
1024 MiB
192
What are the uses of hexadecimal?
Colour values in photo editing software MAC addresses IPv6 addresses Unicode
193
What is an overflow error?
A computer or a device has a predefined limit that it can represent or store (e.g. 32 bits). Once a values falls outside this limit, an overflow error occurs
194
How to convert using a Two’s Complement Signed Integer?
Flip the bits and add 1
195
What is a character set?
Consists of all the letters, numbers and special characters that can be recognised by a computer system.
196
How many characters/bits does the ASCII character set use?
128 characters / 7 bits
197
How many characters/bits does the Extended ASCII character set use?
256 characters / 8 bits
198
How many characters/bits does the Unicode character set use?
65,356 characters / 16 bits
199
What is sample rate measured in?
Frequency in Hertz
200
What is the sample rate?
How often the height is recorded (x-axis)
201
What is the sample resolution?
The accuracy to which the height is recorded (y-axis)
202
What is sample resolution “measured” in?
Bit depth
203
How to calculate file size of a sound file in bytes?
(Sample rate x Sample frequency x Length) / 8
204
What is the colour depth of an image?
The number of bits required to represent the number of colours in the image
205
What is the image resolution of an image?
The number of pixels in the image (i.e. the area of the image ~ b x h)
206
What is the image resolution of an image?
The number of pixels in the image (i.e. the area of the image ~ b x h)
207
What is metadata?
The information that allows us to recreate the image on the screen
208
How to calculate the file size of an image file in bytes?
(Image resolution x Colour depth) /8
209
What file formats use Lossy compression?
JPG, MP3, MPG
210
What are the advantages of Lossy compression?
Biggest reduction in file size Least transmission time Reduces Internet traffic and collisions
211
What are the disadvantages of Lossy compression?
Detail is permanently lost by reducing the colour depth, resolution or rate
212
When would Lossy compression be used?
Music streaming Online images and video Image libraries on devices or in the cloud
213
What file formats use Lossless compression?
TIF, PDF, GIF, PNG, ZIP
214
What are the advantages of Lossless compression?
Original quality is preserved / no information or data is lost
215
What are the disadvantages of Lossless compression?
Less significant reduction in file size
216
When would Lossless compression be used?
Text documents Electronic books High resolution documents
217
What is binary?
Series of 1’s and 0’s that represent values or characters Values are stored in base-2 (denary is in base-10) One binary digit is called a ‘bit’ 8 bits make up one ‘byte’ The maximum size of the integer able to be stored depends on the number of bits used - e.g. the largest number stored by 8 bits is 255
218
Describe the use of binary in computer registers
A register is a location where data that the processor is using can be stored Processors have internal registers that data can be transferred between The register itself is a group of binary cells, where data is stored as a series of 1’s and 0’s.
219
What is binary-coded decimal and where is it used?
A system of writing numerals where each digit is represented by a 4-bit binary sequence Has the advantage that there is no limit to the size of the number: to add another digit, you just need to add a new 4-bit sequence Used in barcodes and arithmetic where every digit has to be retained in a result
220
What is hexadecimal?
Series of the numbers 1-9 and letters A-F that represent values or characters Values are stored in base-16
221
Why is hexadecimal used to represent numbers?
Each hexadecimal digit represents 4 binary digits, so it is shorter to read Easier for programmers to read as more characters are used (not just 1’s and 0’s) Very large numbers can be stored in a smaller amount of space
222
List some current uses of hexadecimal numbers in computing
defining colours in Hypertext Markup Language (HTML) Media Access Control (MAC) addresses assembly languages and machine code debugging
223
What do computers use binary to do?
To represent data, such as numbers, text, sound and graphics To program instructions
224
What is 4 bits known as?
A nibble
225
What is 8 bits known as?
A byte
226
(Exam-style question) Explain one reason why all instructions and data used by a computer are represented in binary. (3)
A processor consists of billions of transistors, each having just two states, on/off The on/off states of a transistor represent the binary digits 1/0
227
(Exam-style question) Describe a ‘bit’. (2)
A bit is short for binary digit, the smallest unit of data in a computer A bit has a single binary value, either 0 or 1
228
(Exam-style question) Give one reason why a computer doesn’t need to know what a binary pattern represents. (1)
The microprocessor hardware only operates on bits, so it has no concept of type or representation
229
(Exam-style question) Write an arithmetic expression to show that 256 different colours can be represented in 8 bits. (1)
2⁸ = 256 colours
230
What can denary numbers also be called?
Decimal numbers
231
(Exam-style question) Explain one reason why the denary number 256 cannot be represented in an 8-bit binary pattern. (2)
The number would be represented in binary as 100000000 You would need 9 bits to store it
232
Convert the following denary numbers into 8-bit binary numbers: a) 203 b) 241 c) 79 d) 100
a) 11001011 b) 11110001 c) 01001111 d) 01100100
233
Convert the 8-bit binary pattern 11011001 into a denary number.
217
234
List two ways of representing signed integer numbers.
Two’s complement Sign and magnitude
235
What happens if the most significant bit of a two’s complement or sign and magnitude pattern is 1?
The number will have a negative value
236
(Example) Convert -10 to binary two’s complement.
Write out the positive number (+10) in binary: 00001010 Flip all the bits: 11110101 Add 1 (00000001) to the result. This gives: 11110110 Therefore, -10 in two’s complement is 11110110
237
(Exam-style question) Convert the denary number -54 to 8-bit binary two’s complement representation. (3)
11001010
238
(Exam-style question) Give the denary value of the 8-bit two’s complement number 11101111. (3)
-17
239
(Exam-style question) Convert the denary number -94 to a binary pattern using sign and magnitude representation. (2)
11011110
240
(Exam-style question) Give the result of adding 00101011 and 00010111. (2)
01000010
241
(Exam-style question) Add the following 8-bit binary numbers: 01010111 + 01011111 Give your answer in 8-bit binary form. (2)
10110110
242
(Exam-style question) Give the result of applying a logical shift left, 2 places, to the 8-bit binary pattern 00010100. (1)
01010000
243
(Exam-style question) Give the result of applying a logical shift right, 3 places, to the 8-bit binary pattern 10111000. (1)
00010111
244
(Exam-style question) Give the result of applying an arithmetic shift right, 1 place, to the 8-bit binary pattern 10001000. (1)
11000100
245
(Exam-style question) Give the result of applying an arithmetic shift left, 1 place, to the 8-bit binary pattern 11101100. (1)
11011000
246
(Exam-style question) Describe one difference between a logical and an arithmetic shift. (2)
An arithmetic shift preserves the most significant bit A logical shift always fills the vacated bits with 0s
247
(Exam-style question) The binary bit pattern 10101101 is equal to the denary number 173. Explain the effect of performing a logical shift right of two places on the binary number 10101101, and state the denary number equivalent after the shift. (3)
The binary number becomes 00101011 after the two-place logical right shift The new binary number’s denary equivalent is 43 In a two-place logical right shift, the binary number is divided by 4; the result of dividing 173 by 4 is 43.25. The right shift produces an imprecise result because it discards the two bits on the right of the binary number, effectively rounding it down to the nearest whole number
248
What happens to a binary number that has been shifted right one place?
It has been divided by 2
249
What type of binary numbers do arithmetic shifts operate on?
Two’s complement binary
250
What type of binary numbers do logical shifts operate on?
Sign and magnitude binary
251
(Exam-style question) Define the term ‘overflow’. (2)
An error that occurs when a calculation produces a result that is greater than what the computer is able to store, or is greater than the number of bits available to store it
252
(Exam-style question) State two consequences of an overflow error. (2)
The program might crash Continued use of an incorrect result in calculations will cause further errors
253
(Exam-style question) Explain one reason why the result of adding two 16-bit binary patterns together must be 16 bits in length. (2)
The registers inside the machine that hold the original patterns have a fixed length, so they cannot hold more than 16 bits
254
(Exam-style question) Describe one way an overflow error can be caused by shifting the 8-bit binary pattern 11000011 left by one position. (2)
Shifting left the original pattern 11000011 gives 10000110 The original 1 in the most significant bit is shifted out, therefore it uses a position that does not exist in the register
255
(Exam-style question) Convert the 8-bit binary number 10110111 to hexadecimal. (1)
B7
256
(Exam-style question) Convert the hexadecimal number E9 to 8-bit binary. (1)
11101001
257
What are some of the uses of hexadecimal notation?
Used to help people deal with long binary digits as they are much shorter in hexadecimal Error code numbers are usually given in hexadecimal when a computer malfunctions Used to represent numerical values in assembly language
258
What is the number of bits true colour uses to code every available colour variation?
24 bits
259
Each colour is represented by three 8-bit binary numbers that can be simplified to three 2-digit hexadecimal ones. What is the benefit of this?
It is much easier to remember and enter the six digits of the hexadecimal number
260
(Exam-style question) Explain why hexadecimal numbers are sometimes used to represent values stored in computers, even though computers do not use hexadecimal numbers. (2)
Large binary numbers can be complicated to read and work with Binary numbers can be simplified by writing them in hexadecimal as fewer numbers are needed, making them easier to read and memorise
261
What base are hexadecimal numbers in?
Base 16
262
What do computers use ASCII and Unicode to do?
Encode characters
263
What does ‘ASCII’ stand for?
American Standard Code for Information Interchange
264
(Exam-style question) Define what is meant by the ‘character set’ of a computer. (2)
The list of binary codes that can be recognised by a computer’s hardware and software
265
(Exam-style question) Describe how ASCII is used to represent characters in a computer system. (2)
ASCII is a 7-bit code, therefore making use of 128 code sequences to represent different English characters
266
How many bits are used to represent characters in the ASCII character set?
7
267
(Exam-style question) The 7-bit ASCII code for the letter ‘Q’ is 81. Give the ASCII code for the letter ‘H’. (1)
71
268
(Exam-style question) The ASCII code for the character ‘C’ is 67. Give the ASCII code for the character ‘M’. (1)
77
269
(Exam-style question) Explain why Unicode was developed. (2)
Any from: Uses a minimum of 16 bits, so it can represent at least 2¹⁶ characters Before it existed, there were many different encoding systems but none could contain enough characters to represent all major languages Standard ASCII only provides 128 different patterns, it can’t represent all major languages/symbols/characters Unicode can represent all languages, ASCII was developed for English
270
(Exam-style question) State what is meant by the size of an image. (1)
The product of the no. of pixels for the image’s width (W) and the no. of pixels for its height (H)
271
(Exam-style question) State what is meant by the resolution of an image. (1)
The number of pixels per unit area of the display
272
What is meant by colour depth?
The number of bits used to encode the colour of each pixel
272
What is the equation to calculate the file size of an image?
Width × Height × Colour Depth (file size measured in bits)
272
(Exam-style question) State what is meant by the term ‘pixel’. (1)
The smallest block of colour in an image
272
(Exam-style question) State what is meant by the term ‘pixel’. (1)
The smallest block of colour in an image
273
(Exam-style question) Describe the factors that affect the quality of a digital image. (4)
The quality of the image is affected by the number of pixels that make it up, therefore, the more pixels the better the image resolution The quality of the image is affected by the number of bits used to encode the colour depth, therefore, if more bits are used, more colours can be displayed
274
How is file size affected if an image has good quality?
The file size will be large
275
What are analogue recordings?
Original sound recordings
276
What are digital recordings?
Recordings that use samples of the sound at regular fixed intervals
277
(Exam-style question) Sound can be represented digitally by taking samples of the original sound. State what is meant by sample rate. (1) (also known as ‘sampling frequency’)
Sample rate describes the number of sound samples that are taken each second
278
(Exam-style question) Describe the effect of increasing the sample rate. (2)
Increasing the sample rate gives a more accurate reproduction of the analogue wave, as more samples are taken with less time between them
279
(Exam-style question) Explain what is meant by the bit depth of a recording. (2)
Bit depth describes the number of bits used to encode the data taken in each sample
280
(Exam-style question) State the effect of increasing the bit depth of a recording. (1)
Allows more data to be stored, meaning the range of sound can be represented more accurately
281
(Exam-style question) The sample rate and bit depth affect the size of the file produced. Name two other factors which will affect the size of the file. (2)
Length of recording Number of channels
282
(Exam-style question) An analogue signal is never fully reproducible in a digital format. Explain one reason why this statement is true. (2)
A digital recording samples the analogue signal at fixed intervals Therefore, the entire analogue signal is not represented in the digital recording
283
(Exam-style question) Describe the steps taken to convert the analogue sound to a digital sound file. (3)
Sample the analogue sound at equal intervals Measure the sound amplitude Give a binary value for each measurement Store data as digital signals
284
What is the equation to calculate the file size of an audio file?
Sample rate (Hz) × Bit depth × Recording length (seconds) (file size measured in bits)
285
What is 1 hertz (Hz) equal to, in terms of samples?
1 sample per second
286
Why is the total file size for CDs doubled?
They are recorded in stereo and so have two channels
287
State what solid line labelled A represents.
The digital signal
288
State what the dashed line labelled B represents.
The analogue signal
289
Give the sampling frequency, including the correct units.
2Hz
290
Give the value in binary of the audio sample at the 4th second.
101
291
(Exam-style question) State the formula used to determine the number of distinct binary patterns for a known number of bits, ‘n’. (1)
2ⁿ
292
(Exam-style question) Describe the reason 4 bits may be the preferred way to store colour depth in an image rather than 8 bits. (2)
Any one from: The increase in colours that cause a slight improvement in quality might not matter to the person viewing the image The image may be on a web page that is transferred over the internet, which needs to load very quickly The higher colour depth file would mean the image takes longer to transfer and loads more slowly
293
(Exam-style question) Explain one reason for reducing the bit depth of an audio recording. (2)
Any one from: Reducing the bit depth reduces the file size, so the audio file will transmit faster Reducing the bit depth reduces the number of distinct values and these may not be noticed by the human ear
294
(Exam-style question) Explain one reason that a 5-bit colour depth is needed to store 24 colours in an image. (2)
Five bits are needed to store 24 colours because 2⁴ = 16, which is less than 24, and 2⁵ = 32, which is the next largest power of 2 greater than 24
295
(Exam-style question) Both kibibyte and kilobyte can be used as measures of file size. Compare kibibyte and kilobyte. (2)
Any one from: Kilobyte is an SI measurement, whereas kibibyte is an International Electrotechnical Commission (IEC) measurement Kilobyte is equivalent to 1000 bytes, whereas a kibibyte is equivalent to 1024 bytes Kilobyte is equivalent to 10³ bytes, whereas a kibibyte is equivalent to 2¹⁰ bytes Kilobyte is a base 10 measurement, whereas a kibibyte is a base 2 measurement
296
Recall the conversions between binary multiples.
1 byte = 2^0 bytes ×1024 ÷1024 1 kibibyte (KiB) = 2^10 bytes = 1024 bytes ×1024 ÷1024 1 mebibyte (MiB) = 2^20 bytes = 1024 kibibytes ×1024 ÷1024 1 gibibyte (GiB) = 2^30 bytes = 1024 mebibytes ×1024 ÷1024 1 tebibyte (TiB) = 2^40 bytes = 1024 gibibytes
297
Recall the number of bytes represented by each of the following: kilobyte, megabyte, gigabyte, terabyte
kilobyte (kB) - 10³ megabyte (MB) - 10⁶ gigabyte (GB) - 10⁹ terabyte (TB) - 10¹²
298
Recall the number of bytes represented by each of the following: kilobyte, megabyte, gigabyte, terabyte
kilobyte (kB) - 10³ megabyte (MB) - 10⁶ gigabyte (GB) - 10⁹ terabyte (TB) - 10¹²
299
Recall the number of bytes represented by each of the following: kilobyte, megabyte, gigabyte, terabyte
kilobyte (kB) - 10³ megabyte (MB) - 10⁶ gigabyte (GB) - 10⁹ terabyte (TB) - 10¹²
300
Give some reasons for why file compression is used.
Less internet bandwidth is used when files are downloaded/uploaded Transfer time is faster Reduced file size / less storage space is needed Smaller files reduce congestion on the internet
301
Describe the purpose of lossless compression.
Reduces file size without deleting any data When compressed data is uncompressed, it is restored completely to the original file
302
Describe how lossless compression works.
Algorithms look for areas of redundancy where same data is stored many times, grouping this data into one reference (this is an example of run-length encoding)
303
Give examples of where lossless compression is used successfully and where it is used less successfully.
Successful uses Text files Graphic files with a low colour depth Less successful uses Audio files 24-bit colour files
304
Describe the purpose of lossy compression.
Reduces file size by deleting some data Changes made are irreversible and original form cannot be retrieved
305
Describe how lossy compression works.
Image files - algorithms analyse image and find areas where there are slight differences, give these area same value and the file is rewritten with less bits Digital sound recordings - small variations in frequency, tone and volume are removed, human ear cannot detect these small differences
306
Give examples of where lossy compression is used successfully and where it is used less successfully.
Successful uses Image files Digital sound recordings Less successful uses Text files Executable software
307
Give 2 examples of lossy algorithms.
JPEG MP3
308
(Exam-style question) Here is a string of data. CCCWWWCCWWWWWWCCC Give the result of compressing the string using a run-length encoding algorithm. (1)
3c3w2c6w3c
309
What is binary?
Series of 1’s and 0’s that represent values or characters Values are stored in base-2 (denary is in base-10) One binary digit is called a ‘bit’ 8 bits make up one ‘byte’ The maximum size of the integer able to be stored depends on the number of bits used - e.g. the largest number stored by 8 bits is 255
310
Describe the use of binary in computer registers
A register is a location where data that the processor is using can be stored Processors have internal registers that data can be transferred between The register itself is a group of binary cells, where data is stored as a series of 1’s and 0’s.
311
What is binary-coded decimal and where is it used?
A system of writing numerals where each digit is represented by a 4-bit binary sequence Has the advantage that there is no limit to the size of the number: to add another digit, you just need to add a new 4-bit sequence Used in barcodes and arithmetic where every digit has to be retained in a result
312
What is hexadecimal?
Series of the numbers 1-9 and letters A-F that represent values or characters Values are stored in base-16
313
Why is hexadecimal used to represent numbers?
Each hexadecimal digit represents 4 binary digits, so it is shorter to read Easier for programmers to read as more characters are used (not just 1’s and 0’s) Very large numbers can be stored in a smaller amount of space
314
List some current uses of hexadecimal numbers in computing
defining colours in Hypertext Markup Language (HTML) Media Access Control (MAC) addresses assembly languages and machine code debugging
315
Binary System
Components inside computers have billions of transistors. Binary is used to represent the transistors inside the component. Transistors can be on or off (1 or 0).
316
Why is binary used?
Components inside computers have billions of transistors. Binary is used to represent the transistors inside the component. Transistors can be on or off (1 or 0).
317
Signed / unsigned integer
An unsigned integer has no positive or negative sign. Signed: -8, +8 Unsigned: 8
318
Why is the binary system used?
Components inside computers have billions of transistors. Binary is used to represent the transistors inside the component. Transistors can be on or off (1 or 0).
319
Overflow
When the result of a binary calculation requieres more bits than are available in the computer hardware (register)
320
Two’s complement, denary to binary
Remove the - sign Convert the number to binary Flip the bits Add 1
321
Two’s complement, binary to denary
Remove 1 Flip the bits Convert to denary Add a negative sign (if the original number started with a 1)
322
Logical shifts
When doubling, shift/move all bits to the left When halving, shift/move all bits to the right
323
Bit
Binary digit
324
Image file size formula
File size(bits) = width(px) x height(px) x colour depth(bits)
325
Hexadecimal
Used to avoid errors when manipulating numbers Represent binary numbers using smaller digits (1 hexadecimal digit = 1 nibble) Computers don’t process hexadecimal 0-F
326
Units
kilobit - 1000 bits megabit - 1000^2 bits gigabit - 1000^3 bits kilobyte - 8 x 1000 bits megabyte - 8 x 1000^2 bits gigabyte - 8 x 1000^3 kibibyte - 8 x 1024 bits mebibyte - 8 x 1024^2 bits gibibyte - 8 x 1024^3 bits
327
Compression
Reduce file sizes by repackging or removing some data
328
Lossless compression
Reduce file size while retaining the exact meaning of the original data. Works by looking for redundancy where the same data is stored many times and groups this data into one reference
329
Lossy compression
It reduces file size by permanently deleting some of its data.
330
How is text represented
Characters in texts
331
How are characters in text represented
Using the ASCII table, each character has a unique bit pattern. Is a 7-bit code, there are 128 sequences/patterns.
332
How to computers record sound
With a microphone (or a recording device) a computer will take samples at a fixed interval (usually thousands of samples per second), it will then convert these values into binary to be stored in a file.
333
Audio file size formula
file size (bits) = sample rate(Hz) x bit depth(bits) x recording length (seconds)
334
Signed and Unsigned integer
An unsigned integer has no positive or negative sign, a signed one does. Signed: -8, +8 Unsigned: 8
335
What do binary digits represent?
They are 0 and 1 and represent the codes for instructions and data.
336
How many bits in a nibble?
4
337
How many bits in a byte?
8
338
How many bytes in a KB?
1024 bytes
339
How many KB in a MB?
1024 KB
340
How many MB in a GB?
1024 MB
341
How many GB in a TB?
1024 GB
342
How many TB in a PB?
1024 TB
343
What is the acronym for remembering the increasing order of file size? BITS –> PETABYTES
Bold - BIT Blue - BYTE Kites - KILOBYTE Make - MEGABYTE Great - GIGABYTE Toy - TERABYTE Planes - PETABYTE
344
What does KB stand for?
Kilobyte
345
What is the magnitude of a KB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^3 bytes or 2^10 bytes
346
What does MB stand for?
Megabyte
347
What is the magnitude of a MB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^6 bytes or 2^20 bytes
348
What does GB stand for?
Gigabyte
349
What is the magnitude of a GB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^9 bytes or 2^30 bytes
350
What is the magnitude of a MB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^6 bytes
351
What does TB stand for?
Terabyte
352
What is the magnitude of a TB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^12 bytes or 2^40 bytes
353
What does PB stand for?
Petabyte
354
What is the magnitude of a PB? HINT: IN TERMS OF 10 TO THE POWER OF N
10^15 bytes or 2^50 bytes
355
True or false: Transistors act as switches which either conduct electricity (represented by the binary digit 1) or they do not (represented by the binary digit 0). The system consists of these two states, so is called a binary system.
True
356
What does it mean to say a number system is base 10?
Each place value is 10 times bigger than the place to its right.
357
Which number system do we use?
Denary
358
Which base does denary use?
Base 10
359
What are place values?
A place value is the value that a digit’s position in a number gives it. For example (for decimal) in the number 356, the digit 5 has a value of 50 whereas in the number 3560, the digit 5 has a value of 500.
360
What does it mean to say a number system is base 2?
Each place value is 2 times bigger than the place to its right.
361
Which base does binary use?
Base 2
362
Which number system does a binary system use?
Binary
363
What is the denary equivalent of 2^0 bits in a byte?
1
364
What is the denary equivalent of 2^1 bits in a byte?
2
365
What is the denary equivalent of 2^2 bits in a byte?
4
366
What is the denary equivalent of 2^3 bits in a byte?
8
367
What is the denary equivalent of 2^4 bits in a byte?
16
368
What is the denary equivalent of 2^5 bits in a byte?
32
369
What is the denary equivalent of 2^6 bits in a byte?
64
370
What is the denary equivalent of 2^7 bits in a byte?
128
371
How many bits does one binary number have? FOR EXAMPLE: 10011010
8
372
What does MSB stand for?
Most Significant Bit
373
What is the MSB?
The bit with the largest value, farthest to the left.
374
What does LSB stand for?
Least Significant Bit
375
What is the LSB?
The bit with the lowest value, farthest to the right.
376
What are bits?
BInary digiTs - they have single binary values of either 0 or 1.
377
What is an integer?
A whole number without decimals (can be positive or negative).
378
What are the three rules of binary addition?
0 + 1 = 1 0 + 0 = 0 1 + 1 = 0 CARRY THE 1 1 + 1 + 1 = 1 CARRY THE 1
379
What is an overflow error?
When a calculation produces a result that is greater than the range of values that the computer can represent or store.
380
What is the most famous example of an overflow error?
The crash of the Ariane 5 space rocket launched by the ESA (European Space Agency) in 1996.
381
True or false: Binary numbers can only be added and subtracted.
False. Addition, subtraction, multiplication and division can be carried out on binary numbers in the same way as denary ones.
382
What base does the hexadecimal system use?
Base 16
383
What is A in hex?
10
384
What is B in hex?
11
385
What is C in hex?
12
386
What is D in hex?
13
387
What is E in hex?
14
388
What is F in hex?
15
389
How many digits are in the hexadecimal system?
16 digits - 0 to 15
390
List the hexadecimal digits:
0 1 2 3 4 5 6 7 8 9 A B C D E F
391
True or false: Computers understand hexadecimals.
False. Computers only understand and use the binary system.
392
Why do we use hexadecimal numbers?
Human limitations - we get confused by large binary numbers so we simplify them by representing them in hex notation. Saves time.
393
How many bits in a colour code?
24 bits
394
How are colour codes represented?
Hexadecimal numbers - far easier to represent the codes as 6 hex numbers than 24 binary ones. EXAMPLE OF A COLOUR CODE: #CC3399.
395
Why are # signs placed before hexadecimal numbers?
To let people know that the number is a hexadecimal number.
396
Give 4 examples of when hexadecimals are used:
Error messages Assembly language programming Colour codes Short-hand for binary numbers
397
ASCII - What is ‘a’?
You can work out any lowercase letter from this by counting up to the letter (ie. z is 122) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
397
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
398
ASCII - What is ‘0’?
You can work out any number 0-9 from this by counting up to the number (ie. 9 is 57) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
399
ASCII - What is ‘ ‘? HINT: SPACE
Convert to binary if needed in that form.
400
ASCII - What is DEL?
127 -> 01111111
401
What is a character set?
The list of binary codes that can be recognised by the computer hardware and software as being usable characters.
402
Why was ASCII created as the first common encoding system for text?
Different manufacturers used to use their own codes for their computers. However, they soon realised that if computers wanted to share information, they needed to also share a common encoding system for text.
403
What does ASCII stand for?
American Standard Code for Information Interchange
404
How many bits does ASCII use?
7 bits. It can represent 128 possible code sequences - these represent English characters and control actions (backspace, shift on, etc.).
405
What is pseudocode?
A language that is similar to real programming language, but is easier for humans to understand although it doesn’t actually run on a computer. It can be easily converted to a regular programming language.
406
Why was Extended ASCII created?
ASCII had 92 printable characters but there was always a need for more to accommodate foreign languages, mathematical symbols and special symbols for drawing pictures.
407
How many bits does Extended ASCII use?
Extended ASCII uses the full 8 bits and was created to cater for foreign languages and graphics characters.
408
How many codes are in the character set allowed by Extended ASCII?
256
409
What can Unicode represent?
Unicode can represent characters in all known languages and writing systems.
410
Why was Unicode introduced?
The Unicode Consortium introduced Unicode due to too many different versions of Extended ASCII developed by different manufacturers such as IBM and Apple.
411
How many codes are in the character set allowed by ASCII?
128
412
How many codes are in the character set allowed by Unicode?
Unicode uses 16 bits, allowing the use of over 65,000 characters.
413
What is a pixel?
A pixel is the smallest possible dot on a computer screen, represented by a number of bits.
414
What are images made up of?
A digital image is composed of many small points of colour or picture elements, pixels for short.
415
How is the size of an image given?
The number of pixels in the width and then the number of pixels in the height. For example, 640 x 480 or 2048 x 1536.
416
How does resolution affect image quality?
Higher resolution, better image quality.
417
What is resolution?
The number of pixels per square inch on the computer screen. The higher the resolution, the better the picture.
418
What is colour depth?
The number of bits used to encode the colour of each pixel.
419
How many colours can be used in an image/graphic if only one bit is used to encode each pixel?
Only two colours can be used (2^1). The 0 represents black and the 1 represents white.
420
A colour depth of three would allow how many colours to be used?
2^3 is 8. So 8 colours could be used.
421
What is the current standard for colour depth (in bits) when representing images?
24-bit representation. This means that the colour data for each pixel is encoded in 24 bits with 8 bits used for each of the primary colours: red, green and blue. Each colour in the palette is a combination of these in different proportions.
422
How many colour variations are allowed by 8-bit encoding?
Using 8-bits allows 256 different levels of each red, green and blue. Therefore 256 x 256 x 256 = 16,777,216 different colour variations are possible. This number of bits produces such a realistic image it is described as being ‘true colour’.
423
In computer science, what are the primary colours?
Red, green and blue
424
I know the number of bits. How can I find the equivalent number of bytes?
Divide the number of bits by 8.
425
I know the number of bytes. How can I find the equivalent number of kilobytes?
Divide the number by 1000.
426
How does colour depth and number of pixels impact file size?
As the number of pixels and colour depth increase, then so will the size of the image file.
427
What is the equation for calculating file size of an image?
W x H x CD (Width x Height x Colour Depth used)
428
How does image quality impact file size?
Better image quality, greater file size.
429
Why is image quality often reduced before transmitting an image electronically?
To reduce the amount of time it will take to download the image after transmitting - there is always a compromise between file size and image quality. Lower image quality = faster download speeds.
430
What is metadata?
Data about data. Included in many files, in addition to the stored data, is information about the file.
431
Give 2 examples of metadata:
When the file was last saved Who created the file What the file is named When the file was created (date/time)
432
What does Exif stand for?
EXchangeable Image File format. The metadata stored in a digital image file contains descriptive and technical information (such as point of capture) and the data is stored in the Exif format.
433
What data could be stored in Exif for image files?
Make and model number of the camera Aperture setting Speed settings Dimensions of the image and the resultant file size
434
What is sound caused by?
Vibrations travelling through a medium such as air, water or metal. These vibrations compress and then pull apart the air molecules thus causing changes in air pressure.
435
Vibrations travel out in waves - what are these called?
Sound waves
436
What do the sound wave vibrations cause in terms of air pressure?
Continuous changes to air pressure. These are shown on analogue diagrams.
437
What are analogue recordings?
Recording methods that try to capture the continuous changes in air pressure by trying to convert all of the changes to analogous changes in voltage.
438
Give 2 examples of analogue recordings?
vinyl albums audio cassettes These can capture the continuous changes in air pressure as minute changes in voltage.
439
Why do computers not use analogue recordings?
Computers are digital. They cannot represent continuous, minute changes in voltage; each transistor is either on or off, nothing in between.
440
What does analogue mean?
Data which can use any value in a continuous range.
441
What is sampling?
Making a physical measurement of the amplitude of the wave at set time intervals and then converting the measurements to digital values. Think of it as similar to making an animation - the smaller the changes between each sample and the greater number used each second, the more realistic the animation.
442
What are the advantages of digital sound files? HINT: ANSWER NAMES 7
it can be edited and manipulated easily by computer equipment it is more portable; it can be carried on a memory stick or SD card while a vinyl record or tape are not as portable it can be played over and over again without deterioration. LPs and tapes deteriorate. it can be easily copied on a computer. Expensive equipment is needed to copy a vinyl record. digital audio files can be easily emailed, downloaded and streamed by users. equipment to record and process digital sound is relatively cheap. it has allowed people to produce their own commercial music at home.
443
What are the advantages of digital sound files? HINT: ANSWER NAMES 7
it can be edited and manipulated easily by computer equipment it is more portable; it can be carried on a memory stick or SD card while a vinyl record or tape are not as portable it can be played over and over again without deterioration. LPs and tapes deteriorate. it can be easily copied on a computer. Expensive equipment is needed to copy a vinyl record. digital audio files can be easily emailed, downloaded and streamed by users. equipment to record and process digital sound is relatively cheap. it has allowed people to produce their own commercial music at home.
444
What are the two factors that impact how accurately a digital recording will match the original sound?
Sample rate and bit depth
445
What is sample rate?
The number of samples taken each second. The higher the sample rate, the more accurately the sound will be represented.
446
For CDs, what is the average sample rate?
44,100 samples per second (44.1KHz)
447
For Blu-ray audio, what is the average sample rate?
96,000 samples per second (96KHz)
448
How many KHz is one sample when converting audio to digital form?
1000
449
What is bit depth when converting audio to digital format?
The number of bits used to encode each sample.
450
How does increasing bit depth impact digital audio quality?
Higher bit depth = more bits used to encode each sample = more accurate representing of range of sound = better audio quality
451
What is the dynamic range?
The range of volume of sound in music.
452
For CDs, what is the bit depth used for digital audio?
16 bits
453
What is the equation for calculating digital audio file sizes?
sample rate x bit depth x length in seconds (x number of channels (mono or stereo) if applicable)
454
What is compression?
Reducing the size of a file so that it takes up less storage space or bandwidth when it is transmitted.
455
What are the benefits of compression? HINT: ANSWER NAMES 5
it uses less internet bandwidth when files are downloaded transfer speed is quicker takes up less storage space on the servers of storage providers smaller files reduce congestion on the Internet, which is good for everyone it makes audio and video files suitable for streaming
456
What is lossless compression?
Compression where a compressed file can be decompressed to the original without any loss of data - all information will remain intact.
457
What is lossy compression?
Compression where data is lost in the compression process and when the file is decompressed it will not contain all of the original information.
458
What is a server?
A computer that provides files on demand to client machines.
459
What is redundancy?
The number of items of data in a file which are repeated.
460
Why are lossless compression rates of 50% relatively easy to achieve with text files?
They have lots of repeated items (words) and characters which are redundant and can be compressed.
461
How does lossy compression reduce file size?
By throwing out some of the data - this is irreversible.
462
Why is lossy compression unsuitable for text or program files?
File size is reduced by throwing out data - a book with missing letters would be unreadable, a program with missing letters/formatting would be inexecutable
463
Why is lossy compression more useful for graphic and audio files?
Because they contain lots of information that can be discarded.
464
What are RAW files?
Image files that have not been compressed and which contain all of the colour data are called RAW files.
465
True or false: RAW in RAW files is an acronym.
False. RAW is not an acronym, it just means that the files is as it was when produced by a camera sensor and has not been compressed in any way.
466
What exactly happens during lossy compression? HINT: WHAT DOES THE ALGORITHM DO?
The algorithm analyses the image and finds areas where there are only slight differences that we might not be able to distinguish. It then gives these the same value so that it can rewrite the file using fewer bits.
467
What does JPEG stand for?
Joint Photographic Experts Group - known for ‘.jpeg’ files.
468
What does WAV stand for?
Waveform Audio Format - known for ‘.wav’ audio files.
469
What are WAV files?
Digital audio files that contain all of the sound data.
470
How many MB would generally be in a 3 minute WAV file?
30 MB WAV file
471
How many MB would generally be in a 3 minute MP3 file?
3 MB MP3 file
472
How large is a WAV file compared to an MP3 file?
MP3 files are often about 1/10th the size of WAV files.
473
What do computer networks enable? Give at least 2 examples of possible uses. HINT: ANSWER GIVES 5.
474
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
475
What is ASCII?
A 7-bit character set that represents 128 different characters
476
What is Unicode?
Unicode uses 8-32 bits per character to represent characters from languages around the world
477
What is a character set?
A set of character codes for each key that can be represented on a keyboard
478
What is a MAC address?
A unique identifier hat is used to identify a device on the internet. It is a 12 character hexadecimal string that is broken down into 2 parts, first part is the manufacturer ID and second part is Unique serial number of that device.
479
Uses of Hexadecimal
Memory Dumps HTML colours
480
Give 3 characteristic of an IP address
Unique address Public or Private Static or Dynamic
481
2 Types of compression
Lossy Lossless
482
Summary of how lossless compression works?
It allows the file size to be reduced without losing any of the original data. It works by searching for patterns and indexing those patterns.
483
Summary of how lossy compression works?
Lossy compression removed data that is not needed, either because a drop in quality is acceptable or the difference can’t be detected by the human eye.
484
Why is lossy compression not good for software, databases, etc.?
Because in lossy compression, parts of the original data are lost meaning the data can’t be put together how it was (bad for code, databases, etc.)
485
Run-length encoding.
It groups repetitive data and stores them once.
486
Dictionary encoding
Dictionary encoding algorithms create an index of data which require less space to store than the original data
487
3 benefits of compression
Download speeds are increased Real-time streaming of audio and video without buffering Takes smaller size on disk, so you have more space to store other data
488
What does compression do?
Reduces file size and changes various attributes of an image file. (eg. file type and resolution)
489
What are the two types of compression?
Lossless and lossy
490
What is specific about lossless compression?
It allows the data to be perfectly reconstructed! (eg. zip)
491
What is specific about lossy compression?
Reduces a file permanently, eliminates certain information (especially unnecessary information) eg. JPG!
492
Which compression is better for saving memory?
Lossy
493
Which compression is better for overall quality?
Lossless
494
why do computers use binary
it is the simplest method for counting available. It is how computer code everything. binary allows for computer to proceed millions of inputs very quickly.
495
reasons for using hexadecimal?
-provides a shorter way to represent a byte of data. -it uses memory, more efficiently
496
what is the ASCII code?
it is the international agreed standard for coding a computer. it is out link between our computer screen and computer hardware. used to translate computer text to human text.
497
examples of ASCII codes?
-web address -URL
498
what is sampling resolution
-The number of bits assigned to each sample. -Also known as bit depth.
499
what is sampling rate?
The number of samples taken in a second.
500
why does Sound need to be converted into binary?
For computers to be able to process it.
501
sound needs to be converted into binary for computers to be able to process it. How is this done?
sound is captured (by a microphone), and then converted into a digital signal. And analogue to digital converter will sample a sound wave at regular time intervals.
502
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
502
how do you calculate file size?
Pixel high x pixel wide x color depth Divided by 8 × 1024
503
how do you calculate the size of a sound file?
mono = sample rate x sample size x time stereo = sample rate x sample size x time (x2)
504
what is data compression?
Is the reduction in the number of bits needed to represent data. Is a method in which the logical size of a file is compressed
505
what are advantages of compressing data?
Save storage speed up file transfer reduce redundancy in stored data
506
what is Lossy file compression?
bigger compression smaller quality When a file is compressed, data is permanently removed
507
what is lossless data compression?
smaller compression higher quality When a file is compressed and restored no data is lost or removed
508
What is the denary number system?
It is a base 10 number system, normally known as the decimal number system.
508
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
509
What is the binary number system?
It is a base 2 number system. It is used for computing. Computers only understand binary.
510
What is the hexadecimal number system?
It is a base 16 number system. It is used by programmers etc. Because of its ease of use as it is 4 times shorter than binary.
511
How to convert from base 2 to bases 10 and 16.
To convert from base 2 to 10, we need to see which binary place values represent the ON state I.e: 1. Then we add all the place values of the ON state. To convert from base 2 to 16, we first divide the binary in groups of 4 each (as base 16 is 4 times base 2), after the grouping we just convert the binary to base 10 and then join all the numbers afyer converting them into base 16 based numbering.
512
How to convert from base 10 to base 2 and 16?
To convert from base 10 to 2, we can use the successive subtraction method where we subtract the number by the biggest possible place value of base 2 until 0 is achieved, and then mark all place values used in subtraction as 1 and others as 0. Or we can use the successive division method where we are supposed to divide the number by 2 until 0 is reached and write the remainders during the process. Then flip the position of all the remainders from end to start to get the converted number. To convert from base 10 to 16, we use the same successive division method but instead divide the number by 16 and not 2.
513
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
514
How to convert from base 16 to 2 and 10?
To convert from base 16 to 2, we write all base 16 numbers individually and then use the successive subtraction or successive division method for each number. To convert from base 16 to 10, we first write all base 16 numbers individually, then multiply them with their respectful place values, then add all the products together to get the base 10 number.
515
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
516
What are some uses of the base 16 system in computers?
They are used in error codes, MAC Addresses, IPv6 addresses and HTML Color Codes
517
What are error codes?
These are the memory location of the error, they allow to trace errors during program development.
518
What are MAC Addresses?
They are numbers which uniquely identify a network device. It refers to the Network Interface Card which is a part of the device. It is usually 48bits but in some cases it is 64bit as well. It is in 6 groups of two hex digits. The first 3 groups (first half) is the identity number of the device manufacturer and the second half is the serial number of the device.
519
What are Internet Protocol (IP) Addresses?
They are the addresses given to any device connected to a network for communication purposes. There are now two types of IP Addresses, IPv4 and IPv6. IPv4 is a 32 bit address while IPv6 is a 128 bit address. IPv4 is represented in denary form and IPv6 is represented in hexadecimal form grouped into 16bit chunks. IPv6 uses a colon as a chunk seperator instead of a decimal point.
520
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
521
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
521
What are Internet Protocol (IP) Addresses?
They are the addresses given to any device connected to a network for communication purposes. There are now two types of IP Addresses, IPv4 and IPv6. IPv4 is a 32 bit address while IPv6 is a 128 bit address. IPv4 is represented in denary form and IPv6 is represented in hexadecimal form grouped into 16bit chunks. IPv6 uses a colon as a chunk seperator instead of a decimal point.
522
What is the relation of HTML with Hex?
HTML is a mark up language used to represent text on a computer. In HTML text can be given colors, and, the color codes are coded in hexadecimal. Where each color spectrum has two hex values which make up 256 values each. As we have 3 basic colors, the total amount of colors available to us are 16,777,216.
523
What is an overflow error?
An overflow error is the error which is produce when a number bigger than the bit size of the register is used resulting in overflow of the register.
524
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
525
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
526
What is an overflow error?
An overflow error is the error which is produce when a number bigger than the bit size of the register is used resulting in overflow of the register.
527
What is a logical shift?
A logical shift is moving the binary number to the left or right. Moving left is basically multiplying it by 2 and moving right is basically dividing it by 2.
528
What is two’s complement?
It is a way of representation for binary numbers where the left most place value is changed to a negative value. A 1 value in the left most bit represents a negative number and a 0 represents a positive number.
529
How to convert a negative number to two’s complement?
First we need to add the negative number into -128. E.g -97 so we will add like this: -128+97. The number we get is the left out numbers we need to put inside the rest of the binary digits to complete the number.
530
What is ASCII?
ASCII, American Standard Code for Information Interchange is a code which is used in computers to represent letters, numbers and symbols/characters on computer and communication systems. It is 7 bit. It was set up in 1963 and a newer version was published in 1986.
531
How is the binary of uppercase and lower case ASCII characters different?
The 6th bit I.e: second most significant bit is a 0 in uppercase and 1 in lower case.
532
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
533
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
534
What is extended ASCII?
It is an 8 bit code which gives us additional 128 codes for use of non English alphabets and other graphical characters.
535
What is the main disadvantage of ASCII?
ASCII can only represent characters of the western languagesASCII can only represent characters of the western languages
536
What is Unicode?
Unicode is the solution to ASCII’s problem. It can represent all languages around the world. Unicode can support upto four bytes per character. The initial 128 characters are the same as ASCII but after that there are several thousand characters.
537
What were the goals with which Unicode was published based on?
To create a universal standard thay covers all languages and writing systems. To produce a more efficient coding system than ASCII To adopt a uniform encoding where each character is encoded as 16 or 32 bit code. To create unambiguous encoding where each 16 and 32 bit value represents the same character. To reserve part of the code for private use so user can assign their own characters and symbols.
538
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
539
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
540
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
540
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
541
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
542
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
543
ASCII - What is ‘A’?
You can work out any uppercase letter from this by counting up to the letter (ie. Z is 90) and then converting to binary. NO NEED TO LEARN ALL OF ASCII.
543
Why computers use binary data?
Because computers are made up of billions of transistors (tiny switches) which are either in the ON state represented by the binary digit 1 or the OFF state represented by the binary digit 0. The base 2 number system is the perfect use for this purpose.
544
What is the denary number system?
It is a base 10 number system, normally known as the decimal number system.
545
What is the binary number system?
It is a base 2 number system. It is used for computing. Computers only understand binary.
546
What is the hexadecimal number system?
It is a base 16 number system. It is used by programmers etc. Because of its ease of use as it is 4 times shorter than binary.
547
How to convert from base 2 to bases 10 and 16.
To convert from base 2 to 10, we need to see which binary place values represent the ON state I.e: 1. Then we add all the place values of the ON state. To convert from base 2 to 16, we first divide the binary in groups of 4 each (as base 16 is 4 times base 2), after the grouping we just convert the binary to base 10 and then join all the numbers afyer converting them into base 16 based numbering.
548
How to convert from base 10 to base 2 and 16?
To convert from base 10 to 2, we can use the successive subtraction method where we subtract the number by the biggest possible place value of base 2 until 0 is achieved, and then mark all place values used in subtraction as 1 and others as 0. Or we can use the successive division method where we are supposed to divide the number by 2 until 0 is reached and write the remainders during the process. Then flip the position of all the remainders from end to start to get the converted number. To convert from base 10 to 16, we use the same successive division method but instead divide the number by 16 and not 2.
549
How to convert from base 16 to 2 and 10?
To convert from base 16 to 2, we write all base 16 numbers individually and then use the successive subtraction or successive division method for each number. To convert from base 16 to 10, we first write all base 16 numbers individually, then multiply them with their respectful place values, then add all the products together to get the base 10 number.
550
What are some uses of the base 16 system in computers?
They are used in error codes, MAC Addresses, IPv6 addresses and HTML Color Codes
551
What are error codes?
These are the memory location of the error, they allow to trace errors during program development.
552
What are MAC Addresses?
They are numbers which uniquely identify a network device. It refers to the Network Interface Card which is a part of the device. It is usually 48bits but in some cases it is 64bit as well. It is in 6 groups of two hex digits. The first 3 groups (first half) is the identity number of the device manufacturer and the second half is the serial number of the device.
553
What are Internet Protocol (IP) Addresses?
They are the addresses given to any device connected to a network for communication purposes. There are now two types of IP Addresses, IPv4 and IPv6. IPv4 is a 32 bit address while IPv6 is a 128 bit address. IPv4 is represented in denary form and IPv6 is represented in hexadecimal form grouped into 16bit chunks. IPv6 uses a colon as a chunk seperator instead of a decimal point.
554
What is an overflow error?
An overflow error is the error which is produce when a number bigger than the bit size of the register is used resulting in overflow of the register.
555
What is the relation of HTML with Hex?
HTML is a mark up language used to represent text on a computer. In HTML text can be given colors, and, the color codes are coded in hexadecimal. Where each color spectrum has two hex values which make up 256 values each. As we have 3 basic colors, the total amount of colors available to us are 16,777,216.
556
What is the relation of HTML with Hex?
HTML is a mark up language used to represent text on a computer. In HTML text can be given colors, and, the color codes are coded in hexadecimal. Where each color spectrum has two hex values which make up 256 values each. As we have 3 basic colors, the total amount of colors available to us are 16,777,216.
557
What is a logical shift?
A logical shift is moving the binary number to the left or right. Moving left is basically multiplying it by 2 and moving right is basically dividing it by 2.
558
What is two’s complement?
It is a way of representation for binary numbers where the left most place value is changed to a negative value. A 1 value in the left most bit represents a negative number and a 0 represents a positive number.
559
How to convert a negative number to two’s complement?
First we need to add the negative number into -128. E.g -97 so we will add like this: -128+97. The number we get is the left out numbers we need to put inside the rest of the binary digits to complete the number.
560
What is ASCII?
ASCII, American Standard Code for Information Interchange is a code which is used in computers to represent letters, numbers and symbols/characters on computer and communication systems. It is 7 bit. It was set up in 1963 and a newer version was published in 1986.
561
How is the binary of uppercase and lower case ASCII characters different?
The 6th bit I.e: second most significant bit is a 0 in uppercase and 1 in lower case.
562
What is extended ASCII?
It is an 8 bit code which gives us additional 128 codes for use of non English alphabets and other graphical characters.
563
What is the main disadvantage of ASCII?
ASCII can only represent characters of the western languages
564
What is Unicode?
Unicode is the solution to ASCII’s problem. It can represent all languages around the world. Unicode can support upto four bytes per character. The initial 128 characters are the same as ASCII but after that there are several thousand characters.
565
What were the goals with which Unicode was published based on?
To create a universal standard thay covers all languages and writing systems. To produce a more efficient coding system than ASCII To adopt a uniform encoding where each character is encoded as 16 or 32 bit code. To create unambiguous encoding where each 16 and 32 bit value represents the same character. To reserve part of the code for private use so user can assign their own characters and symbols.
566
Why is binary used?
Components inside computers have billions of transistors. Binary is used to represent the transistors inside the component. Transistors can be on or off (1 or 0).
567
Overflow
When the result of a binary calculation requieres more bits than are available in the computer hardware (register)
568
Two’s complement, denary to binary
Remove the - sign Convert the number to binary Flip the bits Add 1
569
Two’s complement, binary to denary
Remove 1 Flip the bits Convert to denary Add a negative sign (if the original number started with a 1)

Computer Science Flashcards (6 decks)

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