On 10 Aug 98 at 15:07, Winston Pike wrote:

> I'm trying to increase the cache in my 486DX2-66 from 128K to 256K
> (which is coming from another 486 machine).

  This is probably a good idea, but it may prove easier (read on) to
move the DX2-66 to the other board....

> The current chips are four CY7C199-20PC and one IS61C64AH-15N.

  The IS61C64AH-15N is, I believe, the "tag" RAM.  Since it's the
same in each set, we can ignore it.

  The CY7C199 DRAMs are 8 bits wide, by 32K long.  You can put four
of them together to build a memory array that is 8 bits wide by 128K
long, or one that's 32 bits wide by 32K long.

> The chips I'm replacing with are eight IS61C256AH-20N and one IS61C64AH-15N.

  The IS61C256AH DRAMs are 1 bit wide, by 256K long.  You can put
eight of them together to build a memory array that is 8 bits wide by
256K long.  BUT
  (a) note that the chip boundaries down't run the same way as with
the CY7C199s, and
  (b) there is no way to make a 32-bit wide array with only eight of
them.

  I would conclude that, in order to upgrade your machine to 256K
cache, you're going to need chips that are organized the same way as
the CY7C199s are, because that's what the board was designed to
handle.

David G