18 Nov
2010
18 Nov
'10
3:02 a.m.
Tony Duell wrote:
Later DRAMs had multiplexed
address inputs. of course. Was there a good reason for this other
than to
save package pins?
I don't remember any other justification being given back in the day.
Lower pin count allowed for more chips per unit board area. Prior to
Mostek's invention of the multiplexed-address DRAM, 4K DRAMs were in a
22-pin DIP, which occupied approximately 0.55 square inches, while the
multiplexed-address DRAM in a 16-pin DIP occupied only 0.32 square
inches. (Not counting decoupling capacitors or any additional spacing
needed for power distribution.)
In hindsight, it seems surprising that the "ZIP" package didn't appear
until many years later, since that allowed for twice the packaging
density without moving to surface mount.
Eric