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 ...

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 ...

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 00000000 - 00000000 to 11111111-11111111 65,536
24 24 bits 100100111001-001100111010 00000000 - 00000000 - 00000000 to 11111111- 11111111-11111111 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

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