Word length (bit-depth) by Matt Ottewill

Word length is an enormously important facet of computer systems. In simple terms, word length expresses the number of bits in a byte. For example ... a byte made up of 8 bits (eg "10011101") has a word length of 8. We can also say the byte is 8-bit. In simple terms, the longer the word length the more detailed or precise the information can be, so a 16-bit byte can contain more "precise" or "detailed" information than an 8-bit byte.

Possible values of a byte

Word length determines the number of possible variations a byte can be. For example, there are 16 possible variations in a 4-bit byte ...

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Byte (binary)	Equivalent decimal value
0000	0
0001	1
0010	2
0011	3
0100	4
0101	5
0110	6
0111	7
1000	8
1001	9
1010	10
1011	11
1100	12
1101	13
1110	14
1111	15

See computer counting systems for more on base 2 (binary) and base 10 (decimal) counting systems

Here are some other typical word length values ...

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Word length	Byte length	Example Byte	Possible values	No of values
1	1 bit	1	1 and 0	2
8	8 bits	10010011	00000000 to 11111111	256
16	16 bits	1001001110010011	0000000000000000 to 1111111111111111	65,536
24	24 bits	100100111001001100111010	000000000000000000000000 to 111111111111111111111111	Millions!

Word length and data "quality"

As a general rule ...

The longer the word length the better the quality (or more detailed and precise) the information is, but ... the bigger the file size, and the greater the processing power required to handle it.
The shorter the word length the poorer the quality, but ... the smaller the file size, and the lesser the processing power required to handle it.

Differing word lengths

As a general rule, the bytes in an individual software element (eg an image file, application or system component) will have identical bit-depths. There are some exceptions such as the MP3 format which offers a variable word length option, but this is not the norm.

However, word length may differ between software elements in a single computer system. For example, a system may be dealing with all the following file types simultaneously ...

A GIF image file which will comprise a number of 8-bit (or less) bytes
A CD quality .aif or .wav audio file which will comprise a number of 16-bit bytes
A native RGB Photoshop document which will comprise a number of 24-bit bytes
Elements of an operating system some of which may be 32-bit whilst others are 64-bit

It is possible for a single application to handle different media files of different bit depths simultaneously. For example ... Flash can replay audio, display images and play video files each with a different word length.

Word length and audio

Click here to read how word length effects quality in an audio file.

Word length and images