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GCSE Computing > Memory and storage Part 2 > Flashcards

Memory and storage Part 2 Flashcards

Data Representation

1
Q

What is binary?

A

Binary is a number system consisting of only 0s and 1s

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2
Q

Why must data be stored in a binary format?

A

Computers consist of billions of transistors, which are switches, that only contain two values - on and off. Therefore all data must be represented and processed this way.
Everything that a computer needs to process must be converted into binary format, including text, images, video and audio.

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3
Q

What are the different units of data storage and how many bytes are in each one?

A

1 bit = a single 0 or 1
1 nibble = 4 bits
1 byte = 8 bits = 1 character of text
1KB (kilobyte) = 1000 bytes
1MB (megabyte) = 1000 kilobytes
1GB (gigabyte) = 1000 gigabytes
1TB (terabyte) = 1000 gigabytes
1PB (petabyte) = 1000 terabytes

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4
Q

How many possible combinations or states can 5 switches produce?

A

32 (basically 2 to the power of that number, as binary is a base 2 system)

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5
Q

What is the most significant bit? (MSB)

A

The bit with the largest value (furthest to the left)

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6
Q

What is the least significant bit? (LSB)

A

The bit with the smallest value (furthest to the right)

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7
Q

What is 28 in binary using 8 bit binary?

A

00011100

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8
Q

What is 1010111 in denary?

A

87

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9
Q

What are the 16 times tables (up to16*16)

A

16, 32, 48, 64, 80, 96, 112, 128, 144, 160, 176, 192, 208, 224, 240, 256

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10
Q

What are the powers of 2 (up to 2^20)

A

2 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16348 32768 65536 1310722 262144 524288 1048576

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11
Q

Convert BB from hex to denary

A

187

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12
Q

Convert 106 from denary to hex

A

6A

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13
Q

Convert 83 from hex to binary

A

10000011

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14
Q

Convert 00111110 from binary to hex

A

3E

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15
Q

Why do programmers use hex?

A

It is simpler to remember a hex value than a binary value
It is quicker to write or type
People are less likely to make an error with fewer digits
It is easy to convert between hex and denary
NB: never refer to computers when answer this question, as they only understand binary! Hex is purely for the people!

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16
Q

What is overflow error?

A

When the result of an addition is too large for the number of bits the computer works with, there will be an overflow error

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17
Q

What does a binary shift left of one bit do?

A

it moves all the bits one place to the left, with the vacant bit spaces filling up with zeros, and DOUBLES the number

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18
Q

What does a binary shift right of 2 places result in?

A

It halves the number and rounds down each time, essentially dividing by 4 (2^2)

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19
Q

What are the effects of logical shifts?

A

Logical shifts can very quickly multiply or divide a binary number by a factor of two
A loss of accuracy can occur if 1 bits are removed

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20
Q

Around how many unique characters are available on a keyboard, and therefore how many bits should be used?

A

There are around 98 unique characters, therefore 7 bit binary should be used to represent them

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21
Q

What is a character set and how is it ordered?

A

A character set is a set of letters, numbers, symbols and digits that can be represented by a computer.
Character sets are ordered logically, so the code for ‘B’ will be one greater than the code for ‘A’.

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22
Q

What are the two major character sets in use today?

A

ASCII and Unicode

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23
Q

What is ASCII and what are its characteristics? (Think exam for bits)

A

ASCII is the standard code, used worldwide and uses 7-bit binary codes. Extended ASCII uses 8-bit binary, and that’s what’s going to be used in the exam, so 256 different characters can be encoded.
Characters include numbers 0-9, uppercase and lowercase, letters A-Z, a-z, punctuation symbols and the space character
Originally developed for representing the English alphabet

24
Q

How are character codes grouped on ASCII?

A

Character codes are commonly grouped and run in sequence. Numeric characters 0-9 run consecutively from 48-57 on the ASCII table. A-Z characters are from 65-90 or 01000001 to 01011010. a-z characters use 97-122

25
Q

True or false: the ASCII character code that represents the character ‘7’ is the same as binary code that represents the integer 7 in programming.

A

FALSE! 55(0110111) is the ASCII character code that represents the character ‘7’.
In programming, this is very different to the integer 7 which is represented by 00000111 (7)

26
Q

Can you do arithmetic with characters?

A

No - if a character represents a number it must first be converted to an integer before any arithmetic is carried out.

27
Q

What is the other commonly used character set and why is it used?

A

Unicode is the other commonly used character set, and it is used to represent other characters for different languages, as more characters are needed. Unicode uses 16 bits - so 65,5356 possible combinations.
Unicode is also used to store emoji

28
Q

What is the denary, hex, and binary number range?

A

Denary: 0-255
Hex: 00-FF
Binary: 00000000 - 11111111

29
Q

Kate’s solid state drive on the tablet has 40Gb of space. The camera on the tablet produces images of size 200,000 KB. How many images can she store on the drive? Show all working.

A

200 images

30
Q

True or false: different storage devices have different FIXED capacities

A

TRUE

31
Q

Order the capacity of these different files (nothing is in order):
1 character of text; 1 byte
DVD capacity; 30kB
One small digital colour photograph; 3MB
A full page of text; 650MB
Music CD Capacity; 4.5GB
Hard Disk Capacity; 1TB

A

1 character of text - 1 byte
A full page of text - 30kB
One small digital colour photograph - 3MB
Music CD Capacity - 650MB
DVD Capacity - 4.5GB
Hard Disk Capacity - 1TB

32
Q

What is data capacity?

A

Data capacity is the maximum amount of information that a storage device can hold.

33
Q

Lyla is a social media influencer. She creates images to be shared on her social media accounts.

Each image has a fixed size of 3 MB. She is storing the images on a USB flash drive which has a capacity of 6 GB.
Calculate how many images can be saved on the storage device. Show your working [2]

A

How to answer this question:

Convert 6 GB to MB

Divide the capacity in MB by the files size in MB

Answer

6 GB = 6 * 1000 = 6000 MB

6000 / 3 = 2000 images

34
Q

What is a bitmap graphic?

A

A bitmap graphic is a digital image, which is divided into a grid of picture elements called pixels.
When pixels of an image are mapped to binary codes for their colours, a bitmap is created.

35
Q

What is a pixel?

A

A pixel is the smallest addressable part of an image. It can only have one colour at a time, but it is addressable, meaning that the colour can be changed.

36
Q

What is colour depth?

A

Colour depth is the number of bits used to represent a colour value of a single pixel in an image.
E.g. black and white images (monochrome) allocate 1 bit to each pixel allowing two colours (1 for black and 0 for white) 2^1
2^n = colours; n = no. of bits per pixel

37
Q

What is image resolution?

A

Image resolution is expressed as the number of pixels in an image.

38
Q

How do you calculate the memory required for bitmaps?

A

Memory required = total no. of pixels x no. bits per pixel from colour depth

39
Q

How do you calculate text file size?

A

text file size = bits per character x no. of characters

40
Q

What is metadata? How is it stored?

A

Metadata is a set of standardised information about a picture, meaning data about data. It is stored as part of the file.

41
Q

What are examples of metadata?

A

Width of picture
Height of picture
Resolution of picture
Colour depth
Location of picture
Any type of camera setting (e.g. lens)
Metadata is only talking about pictures - so make sure to give examples that are relevant to pictures only, not just any file

42
Q

What are the characteristics of lossless compression?

A

No information is lost
File can be returned to original condition
Stores information in reduced form which can be used to recreate file e.g long runs of same colour pixels (run length encoding)

43
Q

What are the characteristics of lossy compression?

A

Discards information which is considered less important or can’t be noticed by human eye e.g background
File cannot be reutrned to original condition
More suitable for photographs with every changing pixel colours

44
Q

What are the advantages of using lossy compression over lossless and vice versa?

A
45
Q

What file types are lossy and what are lossless?

A

Lossy compression:
JPEG - used for photos

Lossless compression:
Gif - simple logos only or animated gifs (sequences of images)
png - as with gif, but 24 bit not 8 bit
Tiff - high quality, used for printing

Bmp - original, uncompressed image - editing
Psd - photoshop file - retains layers for editing

46
Q

What is sound?

A

Sound is a vibration of the air (in waves)
causes eardrum to move
brain senses movement as sound

47
Q

What is frequency?

A

Frequency is the number of times sound waves vibrate per second - measured in no. of cycles per second (Hz)
Frequency is pitch
amplitude of wave is loudness

48
Q

How is sound recorded?

A

Micophone (transducer) converts sound waves to electrical voltage signals
Resulting signal is an analogue (or continuous) signal
Computers are digital so need to convert this analoque signal to a digital signal (binary) for a computer to process
Sound is then sampled (converting analogue sound signal into a digital file containing binary numbers
done by ADC

49
Q

What is sampling?

A

Sampling involves measuring the amplitude of a wave at regular intervals. These are then quantised (rounded) into one set number of values and stored together in a binary file.

50
Q

How can you improve the accuracy of a sample?

A

By taking samples at more frequent intervals, the digital signal will come closer to approximating the analogue signal.

51
Q

What is sampling rate?

A

Sampling rate is the number of times sound is sampled per second. Measured in Hz

52
Q

What is sampling depth (accuracy)?

A

Sampling depth is the number of bits per sample (like the sound version of colour depth)

53
Q

What is bit rate?

A

bit rate is the space available for each sample. Measured in kilobits/sec

54
Q

How do you calculate the size of a sound file?

A

size = bit rate x time
(like speed x time)
bit rate = sampling rate x no. bits per sample

so size = sampling rate x sampling depth x time

55
Q

What are the factors affecting sound quality?

A

Sampling frequency (no. samples per second)
Sampling accuracy (no. bits per sample)
Bit rate
amount of storage - file size

56
Q

What are the different ways of storing sound in files and where are they used?

A

WAVE (.WAV) - pure uncompressed sound
high quality
large file size - approx. 2.5MB storage for 1 min
used for CDs

MPEG
compressed sound - removes frequencies ear will not miss or brain cannot process
much lower quality
file size 10 times smaller - 0.25MB for 1 min approx
used on internet/downloads

GCSE Computing (7 decks)

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