View Full Version : Mac Memory vs. PC Memory

November 13th, 2011, 05:52 AM
I have a few 168 pin DIMMs that I'm pretty sure came out of a Mac. I was testing some of my spare memory, and these won't fit in a Pentium II motherboard. The little notches don't line up. They're off by a tiny bit, but enough to make them incompatible. Does anyone know what the difference is? Are these specific to Macs? Or is it just a slightly different type of memory?

November 13th, 2011, 06:05 AM
Those are Mac DIMMs, or if I'm not mistaken, EDO DIMMs. All I know is I tried fitting PC DIMMs into a 5500/250 Power Mac, and they wouldn't fit. I can't remember, but they are either Mac specific, or they are EDO DIMMs.

EDIT - I remember now... they are EDO DIMMs.

November 13th, 2011, 06:30 AM
over the years there have been quite a few types of memory modules that are referenced as DIMM (dual-inline-memory-module (https://secure.wikimedia.org/wikipedia/en/wiki/Dimm))
barring a few really REALLY odd ball modules, they're standardized within their own basic type; FPM, EDO are compatible across the board, as with SDRAM, DDR, DDR2, DDR3. they're distinguished by the physical location of the key (notch) to ensure incompatible modules will not physically fit into sockets.

November 13th, 2011, 06:29 PM
I have used PC-133 DIMMS in a power Mac G4 with no problems. Work like a charm. It could be they were registered DIMMS you were trying to use. I beleive they were keyed slightly differently. Keying is off as you described by a tiny bit.

November 13th, 2011, 10:15 PM
The old early PPC machines used FPM or EDO DIMMs which were 5V I think, so they keyed them so you can put them into a 3.3v SDRAM slot and blow things up.

November 14th, 2011, 03:15 AM
Oh yeah forgot about those. Old age and such