Ethan Dicks ethan.dicks at
Wed Apr 11 10:03:42 CDT 2007

On 4/11/07, Alexandre Souza <alexandre-listas at> wrote:
>     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 have seen memory TI chips in databooks where you had to specify
"upper" or "lower" by part number specifically because they were
bonded out differently *to be piggybacked*.  The memory dice were
identical - what was different was the pinout, by one pin.  It wasn't
an unknown technique back in the day, but it wasn't the favored one.

We had a Qbus COMBOARD that was experimentally altered from 512KB to
1MB by piggybacking a bunch of 50256s on top of the ones that were
already there.  Since we didn't have "upper" and "lower" parts, the
engineers lifted one pin and ran the select line "in the air".

If we could have purchased piggybackable chips, I'm sure we would
have, but they _did_ exist.


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