What does 8-bit mean?

You can think of computer memory as just a vast number of electronic switches that can be turned on or off. The basic unit of data storage in a computer is called a 'bit'. 'bit' is short for binary integer. A bit represents the state of a switches that is either on — the bit has the value "1" ; or off — the bit has the value "0".

More useful data can be represented in a computer by clumping certain numbers of bits together and ascribing a data value to the collective state of the bits in the clump.

An 8-bit data system

The simplest data storage in computers uses clumps of 8 bits at a time. JPEG images are 8-bit data files.

An 8-bit system divides data into bunches of of 8 bits.

The biggest number is represented when all switches are turned on.

on;on;on;on;on;on;on;on = (11111111)

The smallest number is represented when all switches are turned off.

off;off;off;off;off;off;off;off = (00000000)

The next smallest number is represented when all but one switches are turned off.

off;off;off;off;off;off;off;on = (00000001)

Next is off;off;off;off;off;off;on;off = (00000010)

and then off;off;off;off;off;off;on;on = (00000011)

... and so on

There are 256 unique combinations of 1 and 0 when arranged this way. Hence we can number the arrangements from 0 to 255.

0=00000000

1=00000001

2=00000010

3=00000011

4=00000100

5=00000101

.

9=00001001

 

... and so on, up to 255=11111111

using 8-bit data we could store all the numbers from 0 to 255, or, more importantly for digital colour, store every value that is on a 256 step scale.

 

A 16-bit data system

Data can be represented with greater precision in a 16-bit (or even 32 bit) representation.

In a 16-bit system the smallest number is represented when all switches are off.

off;off;off;off;off;off;off;off;off;off;off;off;off;off;off;off (0000000000000000)

The biggest number is represented when all switches are on:

on;on;on;on;on;on;on;on;on;on;on;on;on;on;on;on ... (1111111111111111)

0 =0000000000000000

1 =0000000000000001

.

9 =0000000000001001

.

83=0000000001010011

.

128=0000000010000000

 

.

512=0000001000000000

.

1000=0000001111101000

.

... up to 65535=1111111111111111

using 16-bit data we could store all the numbers from 0 to 65535 or, more importantly for digital colour, represent 65536 different levels of luminosity, for example.

 

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