Coding systems

A binary coding system for storing characters

Seven (or eight, for the more recent extended ASCII) bits are used, with each permutation representing a different character. As a result, it can only represent 128 or 256 characters

A binary coding system that has superseded ASCII

It has backwards compatibility with ASCII. There are two common encodings, UTF-8 and UTF-16, which use 8 and 16 bits respectively. It can represent every character in use in the world

A bit appended to a binary data transmission to check for errors. If the transmissions contains an even number of 1s then the parity bit will be 0, else it will be 1, i.e. it makes the number of 1s even. If the number of 1s is the data received is odd, then it is therefore incorrect

Each bit is transmitted three times, i.e. 101 would be transmitted as 111000111. Therefore, if there are not three consecutive 1s or 0s, there is an error. In this case, the bit with the most occurrences is chosen, i.e. 001 would be assumed to be 0

Some operation is performed on all digits to obtain a one digit number, i.e. repeatedly adding up the digits until a one digit number is reached. This digit is then appended to the number. When the transmission is received, the number is checked to see if it produces the same check digit. To overcome the problem of two digits being swapped around not having an effect on the check digit, each digit may first be multiplied by a different weight, starting at 2, i.e. 23045 would become 26+35+04+43+5*2

width*height (in pixels)

Each pixel is stored individually using one or more bits. They may also contain metadata, normally found at the beginning of the file and including information such as the image’s width, height and colour depth

The number of bits allocated to the colour of each pixel in a bitmapped image

2ⁿ

file size=resolution*colour depth

They are created using objects and coordinates. For example, a line could be stored with just two sets of coordinates, a triangle with three, etc. Other information may include thickness, colour, etc.

• Smaller file size due to not having to store information about every pixel • No pixellation occurs when enlarged

The process of converting analogue sound waves into digital form

A series of readings at fixed intervals are taken from the wave, recording the amplitude

The number of bits allocated to each sample

file size=sampling ratelengthsampling resolution

To faithfully recreate an analogue signal in digital form, the sample rate should be at least twice the value of the highest frequency in the sampled signal

The process of reducing the number of bits required to represent data

Compression where the compressed file has the same quality as the uncompressed file

Compression where some data is discarded and so the resultant file is of worse quality

It eliminates repeated data, i.e. aaaaa may be turned into 5a

Common strings are coded in some way. For example, “tion” may be replaced with a “1”. It can then be decoded again by looking up what string each numeric token corresponds to