11 Apr
2007
11 Apr
'07
4:32 p.m.
On 11 Apr 2007 at 0:00, Steve Thatcher wrote:
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.
What I said earlier. The 128K chips in question are probably nothing
more than the old Rev I PC-AT planar chips. AFAIK, it's not possible
to use any conventionally (64K/256K) DRAM in these sockets without
some PCB cuts and jumpers.
The technique is still being used today: google the phrase "stacked
RAM".
A "cheap and dirty" memory epansion for the Atari 540ST was, if I
remember correctly, to piggyback additional DRAM, with the exception
of one select line, which was run via wire to a different point.
The "half good" memory dates back long before 256K chips--it goes all
the way back to 16K ones. I've got a batch of Intel 2109s that
differ from each other by a suffix -1 or -2. The idea is that the
suffix indicates which half is good; otherwise the chips are
electrically the same. I remember when the local Intel sales guy
dropped off a bag of the things on my desk and I sorted through them
and found a batch where all 16K worked in my application.
Cheers,
Chuck