[sdiy] spectrum memory

[René Schmitz]

Rainer Buchty wrote:

> IIRC they are 4bit wide each and were sort of "defective" chips already
> back in the 80s in a way that they were 8bit chips which failed QC. I
> vaguely remember articles in Happy Computer and c't back then about
> upgrading the Spectrum to full 48kB.

No these were 64k x 1 chips, where the defects were only on either the 
lower or upper 32k, it had to be at the same half on the 8 chips you 
need for the upgrade (indicated by a suffix). There is a jumper wire 
somewhere on the PCB that selects which bank is actually used. A 6164 
can be used IIRC. (Some people did that back then, and added a switch 
for the bank selection, so you got a 80k spectrum.)

Cheers,
  René

-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159