Ram Upgrade: CAS latency?


macrumors 6502a
Original poster
Feb 7, 2003

I've got a Powermac G5 Dual 1.8GHz with 1 gig of RAM (4 x 256 Crucial). Unfortunately it is the 4-ram slot model, so to upgrade RAM any further I'd have to remove a pair of 256 and stick a pair of 512 in there or something.

I can find PC3200 512mb RAM extremely cheap on web sites like Newegg. It's all rated as CAS 3 latency, and it's all off-brand I've never heard of or seen anywhere else (brans like "Wintec", "Ampo", "Rosewill", etc.)

I've read a bunch of web sites that explain exactly what CAS latency means, but no web sites are willing to make a broad claim on the effects of chosing CAS2 RAM over CAS3 RAM. All the web sites I found were like, "CAS2 ram could improve your system performance".

My G5 owner's manual simply says that it takes CAS3 memory. My questions are these: has anyone had experience putting these off-brand memory sticks in their Powermacs? Or should I just stick with crucial? And, given my system, do YOU think it would make a difference in system performance if I went with the (MUCH more expensive) CAS2 memory over the CAS3 memory? I rarely play games, but want a memory upgrade because I need to run memory-hungry applications like MATLAB, and I think a 512mb or 1gig RAM boost might help.

Thanks for your input.

wrc fan

macrumors 65816
If you wanted to switch to CAS2 you'd have to switch all the ram out of your system (well unless your Crucial sticks are CAS2) as the ram will run at the speed of the slowest stick. I don't think most people will really notice any different between the speed, and just having the extra ram will create a nice enough speed boost that you should be happy.

I can't comment on the bands, as I always buy Crucial.


macrumors G5
Apple's word is that CAS latency makes no difference in a Mac as long as the minimum CL3 is met. AFAIK there is no technology like Intel's PAT to improve the motherboard performance with lower latency RAM.

You are right to be sceptical of RAM that isn't tested and guaranteed compatible on Macs. You might be lucky, or you might spend a lot of time and money shipping back RAM that doesn't work (especially on the Mini and iMac G5).

Stick with a reputable seller who guarantees Mac compatibility. In the USA I like www.datamem.com
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