GCSE A* REVISION NOTES


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Representation of data in computer systems

Units

define the terms bit, nibble, byte, kilobyte, megabyte, gigabyte, terabyte

understand that data needs to be converted into a binary format to be processed by a computer.

Circuit only needs to check for two states: electricity flowing or not flowing (on or off) resulting in more reliable circuits.

Number

Explain the use of hexadecimal numbers to represent binary numbers

Hexadecimal numbers are used to represent binary as they are easier to read for humans, they are shorter and they are easier to reference and compare for error analysis.

Character

explain the use of binary codes to represent characters

Each character including symbols, digits, upper and lower case is given a unique character identifier code stored in binary. Some codes are reserved for control characters (e.g. TAB, Carriage Return)

explain the term character set

All the characters which are recognised/can be represented by the computer system

describe with examples (for example ASCII and Unicode) the relationship between the number of bits per character in a character set and the number of characters which can be representeD.

Unicode has a much larger character set and can represent many more characters from all alphabets. Because Unicode uses 16 bits and ASCII uses fewer (7/8 bits) which can only represent 256 distinct characters. Many more characters are needed for coping with all languages and so ASCII does not contain characters used in some languages.

Images

explain the representation of an image as a series of pixels represented in binary

Each pixel is represented by a binary code that tells the computer the colour it has as a mixture of red, green and blue

explain the need for metadata to be included in the file such as height, width and colour depth

Metadata such as height, width and colour depth allow a computer to display an image file correctly.

discuss the effect of colour depth and resolution on the size of an image file

Sound

explain how sound can be sampled and stored in digital form

explain how sampling intervals and other considerations affect the size of a sound file and quality of its playback.

Instructions

explain how instructions are coded as bit patterns

explain how the computer distinguishes between instructions and data.


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