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Jope · 23 September 2006, 10:05

Those eproms have both a byte mode and a word mode.

The smaller 27c2100 part is 256kbitx8 or 128kbitx16..
The larger part is then 512kbitx8 and 256kbitx16.

However both values for each chip naturally come to the same amount in kiloBytes.. It's just the layout of the chip that's different depending on which mode the chip is read in. The Amiga uses the word mode (16bit).

And how to convert.. We start off with the smaller 27c2100 part that should fit a 256kB kickstart image. Remember, that there are 8 bits in a Byte and ROM / RAM chip sizes are reported in bits.

Thus 256kbitx8 is: 256kilobits times 8 (now we have the amount of bits the chip contains without any layout info) divided by 8 to get bytes. So 256kB.
If we look at the chip in word mode, we have 128kilobits times 16 divided by 8.. What's the value in kilobytes?

The explanation above is not 100% thorough, as I'm again feeling very lazy.. But at least you can get a rough idea what it's about.. If you have a 256kx4 part, then it's (256 * 4)/ 8 to get the amount of bytes it stores.

It is important to remember that bits are b and bytes are B. I always cringe when I see people talking about the new "160gb" drive they bought..

23 September 2006, 10:05	#39
Jope - Join Date: Jul 2003 Location: Helsinki / Finland Age: 43 Posts: 9,863	Those eproms have both a byte mode and a word mode. The smaller 27c2100 part is 256kbitx8 or 128kbitx16.. The larger part is then 512kbitx8 and 256kbitx16. However both values for each chip naturally come to the same amount in kiloBytes.. It's just the layout of the chip that's different depending on which mode the chip is read in. The Amiga uses the word mode (16bit). And how to convert.. We start off with the smaller 27c2100 part that should fit a 256kB kickstart image. Remember, that there are 8 bits in a Byte and ROM / RAM chip sizes are reported in bits. Thus 256kbitx8 is: 256kilobits times 8 (now we have the amount of bits the chip contains without any layout info) divided by 8 to get bytes. So 256kB. If we look at the chip in word mode, we have 128kilobits times 16 divided by 8.. What's the value in kilobytes? The explanation above is not 100% thorough, as I'm again feeling very lazy.. But at least you can get a rough idea what it's about.. If you have a 256kx4 part, then it's (256 * 4)/ 8 to get the amount of bytes it stores. It is important to remember that bits are b and bytes are B. I always cringe when I see people talking about the new "160gb" drive they bought.. Last edited by Jope; 23 September 2006 at 10:15.