AMSTRAD cpc 6128 User Instruction page 383

.... so the columns look like:
1
o o
1 1
(16
+
o
+
o
+
2
+
1)
=
19
In order to provide a shorthand method of referring to binary digit information, the
term 'byte' is used to denote 8 bits of information. The maximum number that be
stored in a byte is then (binary) 11111111- or (decimal) 255. This implies 256 actual
variations, including 00000000, which is still perfectly valid data to a computer.
Computers tend to manipulate data in 8 bit multiples. 256 is not a very large number,
so in order to achieve an acceptable means of handling the memory, two bytes are
used to provide a method of addressing memory which is in the form of array, with a
horizontal and vertical address by which the elements of that array can be located:
0 1 2 3 4
5 6 7
8 9
0
1
2
3
4
5 1 1
6
7
8
9
The array can locate up to (10xl0) items of information using address numbers that
lie in the range 0 to 9. The item stored at position 3,5 is a '1'
~
as is the item at 5,5.
So a binary array of 256x256 can handle 65,536 individual locations using 8 bit
addresses for the vertical and horizontal axes of the array. So our '0' and '1' have
progressed to being capable of identifying one of 65,536 different elements.
Chapter 9 Page 10 At your leisure ....