Data Representation Flashcards
Why do computers use binary to represent all forms of data?
- Any form of data needs to be converted to binary to be processed by a computer
- Data is stored using 1’s and 0’s
Describe how bits are represented on a HDD:
- a platter contains billions of tiny magnetic grains.
- each grain independently magnetized (to store a 1) or demagnetized (to store a 0)
Describe how bits are represented on an optical disk e.g. CD/DVD/BluRay
Pits and lands used to represent 1 or 0 on the surface of a CD
A laser shines onto the surface of the disc and the reflection is measured
What is denary?
Denary is the standard number system used around the world
Denary is known as base 10 because there are ten choices of digits between 0 and 9
Each digit has a place value (powers of 10)
What is binary?
Binary is a number system used in computing
Binary is known as base 2 because there are 2 choices of digits , 0 and 1
Each digit has a place value (powers of 2)
Explain the difference between the binary and denary number systems
- Binary base 2 system
- Denary base 10 system
- Binary has 2 digits (0 and 1)
- Denary has 10 digits (0-9)
- Binary place values are powers of 2
- Denary place values are powers of 10
What are the binary place values for a byte?
128 64 32 16 8 4 2 1
Convert the 8 bit binary number 10011011 into denary
155
Convert the following binary numbers into denary
00011101
00100101
01010101
10010100
00011101 = 29
00100101 = 37
01010101 = 85
10010100 = 148
Convert the denary value 156 into binary
10011100
Convert the following denary numbers into 8 bit binary
96
72
161
74
96 = 01100000
72 = 01001000
161 = 10100001
74 = 01001010
What is the largest value that can be stored in 8 bits?
255 (128 + 64 + 32 + 16 + 8 + 4 + 2 + 1)
What is the largest value that can be stored in 10 bits?
1023 (512 + 256 + 128 + 64 + 32 + 16 + 8 + 4 + 2 + 1)
How many bits in a byte?
8
How many bits in a nibble?
4
How many nibbles in 4 bytes?
8
What is hexadecimal?
- Base 16 number system
- 16 choices of digits (0-9, A-F)
- Place values are powers of 16
What are the place values for the hexadecimal value A7F3?
- 4096 256 16 1
- A 7 F 3
What is the denary value of the hex digit A?
10
What is the denary value of the hex digit E?
14
What is the denary value of the hex digit 7?
7
Convert the hex value AAA to Denary
2730
Convert the following hex values to denary
- 1F
- 42
- CC
- 1F = 31
- 42 = 66
- CC = 204
Convert the hex value CA to Binary
11001010
Convert the following hexadecimal values to binary
- B3
- 5A
- B0F
- B3 = 1011 0011
- 5A = 0101 1010
- B0F = 1011 0000 1111
Convert the binary value 1111 1010 to hexadecimal
FA
Convert the following binary values to hexadecimal
- 1011 1101
- 1010 0110
- 1111 1010 1100 1110
- 1011 1101 = BD
- 1010 0110 = A6
- 1111 1010 1100 1110 = FACE
Convert the hex value AB to Denary
171
Convert the denary value 166 to hexadecimal
A6
Convert the following denary values to hexadecimal
- 22
- 42
- 170
- 22 = 16
- 42 = 2A
- 170 = AA
Why do we use hexadecimal?
- Easier for programmers to read and understand
- Conversion to binary easier than denary to binary
- Takes up less space when displayed or printed
- Faster than binary for entering numbers
Where is Hexadecimal used?
- HTML colour codes e.g. red = #FF0000
- Display MAC (Media Access Control) addresses e.g. 01-23-45-67-89-AB-CD
- Display ASCII or Unicode values e.g. %41 = 65 = A
- Display error codes e.g. error #404 page not found
- Display memory dumps e.g. 5F 3A 09 F1
What is a character set?
A character set is a complete set of the characters and their character codes that can be recognised by a computer system.
What is character code?
A value/binary number that represents a character
What is ASCII?
- American Standard Code for Information Interchange.
- It is a code for representing 128 English characters as numbers
- Each character is assigned a number from 0 to 127
How many bits does ASCII use?
7 bits
How many characters can be represented using ASCII?
- Uses 7 bits so …
- 000 0000 to 111 1111 = 0 to 127 = 128 unique characters (2^7)
How many bits does extended ASCII use?
8
How many characters can be represented using extended ASCII?
- 0000 0000 to 1111 1111 = 0 to 255 = 256 unique characters (2^8)
How many bits does Unicode use?
16
How many characters can be represented using Unicode?
- Uses 16 bits so … 65536 unique characters (2^16)
Describe the difference between ASCII and Unicode
- ASCII uses 7 (or 8 bits) and can represent 128 (or 256 characters)
- Unicode uses 16 bits and can represent 2^16 characters.
Describe one advantage of Unicode
Can represent a wider range of characters and therefore more languages than ASCII
Describe one disadvantage of Unicode
Each character uses more memory space than ASCII
Describe what is meant by a character set
- All the characters and symbols that can be represented by a computer system.
- Each character and symbol is assigned a unique value.
What is a bitmap image?
A collection of pixels where each pixel is assigned a value that represents it’s colour.
What is a pixel?
Short for picture element
The smallest block of colour in an image
What is colour/bit depth?
The number of bits used to represent the colour of a single pixel
How many colours can be stored using 1-bit?
2
There are 2 possible values - 0 or 1
How many colours can be stored using 2-bits?
4
There are 4 possible values (00, 01, 10, 11)
How many colours can be stored using 4-bits?
16
Range of possible value is 0000 - 1111 = 0 - 15
For n bits you can store 2^n different colour codes.
How many colours can be stored using 12 bits?
4096 (2^12)
What is image resolution?
The number of pixels in the image e.g. 600 px x 400 px = 240 000 px
How do you calculate the size of an image?
image size = number of pixels x colour depth
If a 12-bit colour depth is used and the image size is 800 x 600 pixels, what is the minimum file size for the image in bytes?
Number of pixels = 800 x 600
Number of bits per pixel = 12
Total number of bits = 12 x 800 x 600 = 5760000
Number of bytes = 5760000 ÷ 8 = 720000 bytes
What is meant by image metadata?
Image files usually also contain metadata .
Metadata means ‘data about data’
It provides additional information about the image.
Computers needs this data to interpret the file
Give 3 examples of image metadata
file format - eg JPG, GIF, BMP, PNG
resolution
colour depth
time/date the image was taken
camera settings
GPS data
Explain how captured camera images are converted to digital photo files
Image is turned into pixels
Pixels form a grid
Each pixel is give a binary value
Each pixel is given a colour
Pixels are stored in the correct sequence
Meta data is also stored about the image e.g. dimensions/resolution/colour depth
Different file formats are used e.g. JPEG
What happens when you increase the colour depth of an image?
The quality of the image increases
You are more accurately able to represent the range of colours
Also increases the memory size of the image
What happens when you increase the number of pixels in an image?
The density of pixels in the same sized area increases
More pixels per inch, improving sharpness
Can enlarge without visible loss of quality
Increases the memory size of the image
