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Koralatov · Sep 13, 2007, 03:55 PM

If I mix PC100 with PC133 SDRAM in a 500MHz G4 PowerMac, is it likely to go kablooey? I know that you can use 133 even though it's only technically rated at supporting 100, as the RAM 'falls back' to the lower speed, but will using two different speeds cause headaches and/or potential damage for the Mac?

reader50 · Sep 13, 2007, 03:57 PM

You should be fine. All sticks will run at 100, assuming they have the proper speed settings for running at 100. If not, chances are you can fix it with DIMM First Aid from OS9.

reader50 · Sep 13, 2007, 04:16 PM

Note: My above answer assumes your G4 requires PC100.

If your G4 requires PC133, then the 100 modules will not be recognized and there is nothing you can do to change that. Other than buy some PC133 (or faster) of course.

Koralatov · Sep 13, 2007, 04:21 PM

Originally Posted by reader50

Note: My above answer assumes your G4 requires PC100.

If your G4 requires PC133, then the 100 modules will not be recognized and there is nothing you can do to change that. Other than buy some PC133 (or faster) of course.

The PM in question only requires PC100. I'm basically asking because it already has a 512MB PC100 DIMM in there, and I've come across a good seller on eBay that sells PC133s cheaper than I could get 100s new, and I'd hate to have to replace the existing 512MB running at 100 with a 512 @ 133.

Thanks for the really quick reply—much appreciated!

reader50 · Sep 13, 2007, 04:33 PM

Be careful of 512 modules, the G4s are picky about them. You want low-density modules, preferably tested to work in Macs. The majority of PC 512 modules either don't work at all, or come up as 256 modules.

Lateralus · Sep 13, 2007, 04:49 PM

Originally Posted by reader50

Be careful of 512 modules, the G4s are picky about them. You want low-density modules, preferably tested to work in Macs. The majority of PC 512 modules either don't work at all, or come up as 256 modules.

Huh?

I have never heard of any such thing. And I've been through more Power Mac G4s with more RAM configurations than I could ever remember.

reader50 · Sep 13, 2007, 06:08 PM

When Apple designed the G4 memory controller, 512 modules existed only as engineering samples. Apple made a guess at the maximum column count, and the maximum row count. These got designed into the G4's northbridge.

Several years later, when 512 MB modules became common, the industry had settled on a different column / row count in most modules, often referred to as "high density DIMMs". When one of these is plugged into an earlier G4, it will either not be recognized, or come up as a 256 module, depending on which way it's out of sync with what Apple designed for. This problem seems to be exclusive to 512 modules, 256's always seem to work.

This problem (being finickey with the 512 size) affects all of the PC100 G4s. It doesn't affect the Yikes, since that one only goes to 256 modules anyway. I'm not sure about the PC133 G4s.

I have run into this personally, buying a 512 generic PC stick once. It wouldn't recognize at all. Passed it on to a PC friend, it worked perfectly. Passed all tests. A low-density 512 module I bought later, spec'd to work in Macs, worked perfectly in my G4.

Koralatov · Sep 13, 2007, 06:08 PM

Originally Posted by reader50

Be careful of 512 modules, the G4s are picky about them. You want low-density modules, preferably tested to work in Macs. The majority of PC 512 modules either don't work at all, or come up as 256 modules.

I'm with Lateralus on this one: I've heard of Macs being picky and not accepting memory, but I've never heard of them registering it at the wrong size. However, it's not going to be a problem as the eBay seller (scrumpymacs) pulls them from G4 systems anyway, so I know they'll work. They also have a seven-day money back guarantee, and I've dealt with them before, so I'm pretty confident.

Lateralus · Sep 13, 2007, 06:12 PM

Indeed. I have never had any such issues. And, as I said, I've been through enough early G4s and enough sticks of RAM to stock a computer parts warehouse.

While I have no doubt that there are a select few DIMMs that earlier Power Mac G4s will have issues with, it is not the norm. And certainly not the 'majority' as you eluded to.

reader50 · Sep 13, 2007, 06:21 PM

I'm going to let others jump into this one, with their experiences, rather then argue. However, my description is correct. The majority of 512 modules sold at the time from PC-centric stores (like newegg or assorted RAM discount outlets) either would not function, or would not function at full size in the G4s. The more expensive brand-name 512s were somewhat more likely to work, and there was no problem in reverse. A 512 module that worked in a G4 would work in a PC.

SirCastor · Sep 13, 2007, 08:07 PM

This is my primary machine, listed in my sig. Sawtooth from early 2000.