11 May
2012
11 May
'12
10:41 a.m.
posible it was something that was used in the ge workmasters?
On Fri, May 11, 2012 at 12:28 PM, B. Degnan <billdeg at degnanco.com> wrote:
>
> There was some debate at VCF East whether this "IBM 256KB Memory
> Card" P/N 6407740 is a bubble memory card (pic below). The card was
> on display with my IBM PC 5150 exhibit. I originally pulled it from
> an IBM 5155 portable.
>
>
http://www.vintagecomputer.net/ibm/5155/ibm_256KB_memory_card_6407740.jpg
Typically you don't see 32-pin 64K RAM chips on a ISA card. That
does not make it bubble memory though, so I put this out to the
esteemed CCTECH community for answers/ideas.
I doubt very much if it's bubble memory, for sevrral reasons.
I do wonder why it existed. It is trivial to put 640K on the motherboard
of a 5155, jsut as in a 5160 (XT). It's a matter of putting the right
TAMs in (41256s in banks 0 and 1, 4164s in banks 2 and 3), adding a
74S158 (or 74F158) in the enpty socket towards the front and jumpering E1 to E2.
UPDATE: I did not find the card listed in any manuals that I have, but I
did find a reference to the 32-pin DRAM. If I were to guess, you'll find
this card as an option specific to the IBM 5155 portable, to boost the
system up to 512K. It's a small card, perfect for the smaller 5155
chassis. I should mention that I got this particular 5155 with the 256KB
RAM card from an old IBM tech who wanted to find a home for some of his
bench gear.
Bill