11 Apr
2007
11 Apr
'07
2:51 p.m.
the IBM AT used two 64K piggybacked chips for a total of 128K. I don't have the chips
is front of me right now, so I can not tell you if they were MOT chips or not.
As for possibilities, all one has to do is approach a chip mfg and ask them to create the
bond out of the chips so they can be piggybacked. Not all that hard when you have money to
throw at a company. I am sure that is what IBM did. All that would need to be done is swap
an unused pin with a chip select pin. One line goes to the top chip and the other goes to
the bottom chip. Power, RAS, CAS, address and data can all be connected together.
best regards, Steve Thatcher
By the way, I did not read any of the other posts on this topic, so please forgive my
intrusion if not helpful.
-----Original Message-----
From: Alexandre Souza <alexandre-listas at
e-secure.com.br>
Sent: Apr 11, 2007 7:19 AM
To: "General Discussion: On-Topic Posts Only" <cctech at classiccmp.org>
Subject: Re: MCM66128L20
>That's the first thing that puzzles me. It
was my understanding that
>these were 128Kbit chips, so 18 of them would give you 256K bytes (+
>parity) of memory. Can you confirm, please, that 18 of them really are
>512K
>> The top chips are stamped MCM66128L20; the bottom chips have no part
>> number.
Maybe the bottom chips are just EMI filters/pull ups??? :oO
There are NO possibilities that memory can be piggybacked this way. When
you piggyback two memory chips, at least ONE of the pins must be routed
separately. At least this is what logic tells me.
I never seen a 128K *D*ram chip. SRAM exists. This is something that is
driving me crazy here, I cannot find any datasheets/pinouts on this part
number, nor any kind of info. Crazy.
IF the memory was 16-bit-word, maybe you could be using 256K chips
What was the replacement part you got?
Greetings,
Alexandre