Working out Memory Size

[AMSDOS]

I was trying to ask myself why a 320x200 resolution doesn't necessarily equate to 64k because a CPC only has roughly a 17k Screen. 320x200 gives me a figure of 64000 then I multiply that by 2 bits because that's the requirement for the amount of colours on a CPC it's 4 which gives me a figure of 128000, but then if I divide this by 8 I get 16000! But the book doesn't explain where they get the figure of 8 from! Anyone know?? 

[steve]

The unit of memory is called a byte, a byte is 8 bits, so you divide the number of bits (128000) by 8 to give you the number of bytes used to store the data.

[AMSDOS]

Thanks!