From:
Mark Kahrs
there are very nice SRAMs available: for example,
the Cypress
CY62167
is a 2Mx8 1Mx16 RAM in 48 pin TSOP. So you'd
need two ...
(n.b. there is a 4Mx8 but it's only in BGA, so fuggitaboutit).
Actually, one 4Mx8 (assuming it's really only 8 bits wide) wouldn't be as
easy to work with as two 2Mx8; since most QBUS cycles are 16-bit word,
not
byte, you'd have to do two memory cycles for each QBUS cycle -> more
complexity.
And for the 11/70, we're talking about 32-bit wide memory...