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18908305
GCSE AQA Computer Science - Data Representation
Description
All of data representation for AQA comp sci
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gcse
aqa
computer science
data representation
computing
data representation
gcse
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Resource summary
GCSE AQA Computer Science - Data Representation
Images
Bitmap images are made up of picture elements, or pixels
A pixel is a single point in a graphical image
Resolution - concentration of pixels in a certain area
Colour depth - how many colours can be represented in a single pixel
File size = total pixels x colour depth
Higher resolution / colour depth = higher quality & higher file size
Sound
Microphones record analogue and convert to digital
Speakers convert from digital to analogue
Sample resolution - the amplitude used to record each sample / measurement
Sample rate - number of samples taken a second
File size = sample rate x resolution x time
Compression
Lossy
JPG, GIF, MP3
Permanently removes some data
Uncompressed data is not the same as the original
Lossless
PNG, TIFF
Uncompressed data is same as the original
File quality is not lost
Run length encoding
Huffman tree
Analyses the frequency of characters in a body of text
Characters are placed in a binary tree structure
Most common characters appear near the top of the tree
Number systems
Denary
Base 10
The number system we use
Binary
Base 2
It is the only thing a computer understands
Made up of 1's and 0's
Binary addition
0 + 0 = 0
0 + 1 = 1
1 + 1 = 10
1 + 1 + 1 = 11
Logical shifts
Each left shift multiplies the value by 2 (unless there is an overflow)
Each right shift divides the value by 2 (unless there is an underflow)
Hexadecimal
Base 16
Made up of the numbers 0-9 and the letters A-F
Used as a shorter way of representing binary
Can be used to represent colours
Computers do not understand hexadecimal
Storage
Bit - a single 1 or 0
Nibble - 4 bits
Byte - 8 bits
Kilobyte - 1000 bytes
Megabyte - 1000 kilobytes
Gigabyte - 1000 megabytes
Terabyte - 1000 gigabytes
Text
ASCII
7 bits per character
Encodes 128 characters
Only represents the English alphabet
Extended ASCII
8 bits per character
Encodes 256 characters
Used to represent more symbols / special characters
Unicode
Made so that different languages could be represented
16 bits per character
65536 possible characters
First 128 characters use the same codes as ASCII - backwards compatability
Media attachments
2019 08 15+16 42 00 Window (binary/octet-stream)
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