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BurntSmore 03-16-2005 07:13 PM

Matching RAM?
What exactly is matching or pairing RAM? I have seen it in other threads and I don't have a clue of what it means.

Kokopelli 03-16-2005 07:55 PM

It means that memory should be installed in pairs and that they should be the same size, speed, latency, etc... The most common reason for thus requirement is Dual Channel memory architectures or an old system that uses SIMMS. Other than Dual Channel DIMM Banks though I can't think of why a modern system would require it.

Depending on the system if you put in two non-matching peices of RAM into a single bank it would either not boot, not recognize that bank, or run in Single Channel mode. The first two pretty much mean the system will not run, the last means you are cutting memory performance almost in half.

BurntSmore 03-16-2005 08:12 PM

Does that apply to an iMac G5? So, if it does, would it be bad if I install one 1 gig of RAM in addition to the 256 mb that came with the iMac?

Kokopelli 03-16-2005 08:20 PM

It looks like it should be fine with mismatched modules.


Originally Posted by Apple Support
iMac G5 computers work with memory modules (DIMMs) that meet all of these criteria: PC3200, unbuffered, nonparity, 184-pin, 400Mhz DDR SDRAM.

There are two RAM slots. The maximum amount of RAM you can install is 2 GB. You can use RAM module sizes of 256 MB, 512 MB and 1 GB, in either slot.

DIMMs with any of the following features are not supported in the iMac G5 computer: registers or buffers, PLLs, ECC, parity, or EDO RAM.

Always follow the upgrade instructions for Memory and AirPort Extreme card installation as written. Never attempt to remove screws that are not listed in the upgrade instructions.

EDIT: Or maybe not.

If that hint is accurate it sounds like the iMac is a dual channel memory architecture. In this case it seems to be one of the ones that reverts to single channel if the RAM is mismatched. Keep in mind this does not mean that it will not work, merely that it will be faster if the RAM match.

wancarlos 03-17-2005 12:35 PM

I have just bought a G5 and had it kitted out with 2gb of Ballistix Ram from Crucial. There is a massive difference in all operating tasks (especially Photoshop CS).

I know the RAM modules are a little more expensive, but by golly - it's worth every penny. And when I get some more foreigners done, I am getting 2gb more!!!! It's that good!

whoriental 03-17-2005 10:42 PM

ok so what about powerbooks?? does the ram need to match??

warrenbert 03-17-2005 10:55 PM

Installing matched pairs of RAM only applies to Powermac G5s or PCs with dual channel memory.

All other Macs including portables just need to have RAM modules that meet or exceed the minimum specifications, but multiple modules do not otherwise have to be exactly alike.

End of story.

Kokopelli 03-17-2005 10:59 PM

Also you have a 12" Powerbook, which only has a single slot. So the question is moot anyway. Warrenbert is correct though.

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