View Full Version : What does a composite simm look like?

November 27th, 2010, 05:14 PM
I want to upgrade my Mac plus to 4MB before selling it.
The internet says not to use composite simms, but gives little info on how to tell the difference.

The only 1MB chips I have are Goldstar branded, single-sided with 3 chips.
What is that likely to be?

November 27th, 2010, 06:14 PM
Sounds like a composite--i.e. more than one bit width per chip. You want one with 8 or 9 chips on it.

November 27th, 2010, 09:53 PM
Old macs generally use 8 chip SIMMs (no parity).

http://macplus.mia.net/installram.html <== you need to remove a resistor for the system to see all 4MB.

November 28th, 2010, 08:55 AM
Old macs generally use 8 chip SIMMs (no parity)

Most 9-chip SIMMs will work, but the parity is ignored. For that matter, a lot of PCs of that day could be set to ignore parity.

Back then, memory was expensive (you could go to the back pages to PC World and see lots of outfits offering to buy your old memory). One of the uglier "shortcuts" used by some SIMM vendors was to generate the parity bit from 8 RAM chips than to actually store it.

December 6th, 2010, 08:29 AM
Ah, then I'm out of luck unless I find more SIMMs I guess.

December 6th, 2010, 10:01 AM
I vaguely recall Mac Plus don't play nice with 3 chip 1MB simms which incorporated 4Mb parts.

January 6th, 2011, 06:16 PM
Composite SIMM is a SIMM with a lot more chips on them. Think of them as the 4Mb SIMMs that have a LOT of the 1Mb chips on them. They are big, ugly monstrosities that present too much of a load the the chips driving the socket.