[coho]

here's an interesting question for the enthusiasts...i'm a pc guy looking to add some memory to a computer illiterate friend's 1.8ghz/20" imac g5 so he can actually meet the system requirements for world of warcraft (he currently only has 256mb).

Either I'm not searching in the right places or there is very little information out there because i can't find very detailed information of memory configurations in the imacs. because i'm a 21 hour drive away from the machine i also can't inspect it myself. from what i understand, macs are pretty finicky when it comes to spd timings for dimm compatibility correct? and i also understand that the 256mb dimm that came with the machine is pc3200 and likely has timings of 3-3-3-8.

now, i could purchase another 1gb stick of memory of the same timings and add it to the machine OR...i was wondering about maybe trying to get "more power". You see, upon reading this article: http://developer.apple.com/documenta...y05/index.html

it seems that the g5's can accept cas 2 memory??!! i see that powermacs can handle it So...i was wondering if anyone has any insight onto the viability of me say removing the default 256mb dimm and adding 1gb of cas 2 memory? in searching any way i know how i can't seem to find any information on this. I'd also be interested to know whether or not the imac's performance would actually benefit from cas2 and/or 1gb of cas2 would result in more or less gaming performance than compared to 1.25gb of cas3? Any help or pointing in the right direction would be greatly appreciated. Thanks in advance.

Sincerely,

Dan

[mduell]

The CAS2 RAM should work fine in the iMac (and if it doesn't it's probably for reasons unrelated to CAS timing), but the iMac doesn't support timings that fast so it will run it at CAS3. You may as well leave the 256MB in.

As a side note, the performance difference from reducing the memory timings are minimal at best.

[coho]

Originally Posted by mduell

The CAS2 RAM should work fine in the iMac (and if it doesn't it's probably for reasons unrelated to CAS timing), but the iMac doesn't support timings that fast so it will run it at CAS3. You may as well leave the 256MB in.

As a side note, the performance difference from reducing the memory timings are minimal at best.

hi mduell,

thanks a lot for your prompt reply; much appreciated.

yeah i generally thought that imacs couldn't handle lower latencies but...the article i quoted is from the apple developer's website?! *shrugs*

thanks for the article as well. i've actually read it before. it's a little hard to compare the results of that article with this situation though...with it being different hardware & cpu platforms all together. i have no idea whether or not latency causes more or less or the same impact on the powerpc and its memory management.

They did have noticeable differences at lower resolutions where the game was cpu bound.
In addition, with their particular case...they compared cl 2.5 versus 2... whereas the jump in my case would be larger going from 3 to 2. In shopping around for 1gb dimm prices... i was able to consistently find dual channel kits for less than a single low latency 1gb dimm. I figured if i can score the lower latency memory for a couple dollars more, may as well scoop it.

So taking that into context i guess it'll depend on whether the game is cpu or gpu bound...and i have no idea of the computing power of the 1.8ghz cpu in this thing. I'm anticipating that the FX 5200 will be the limiting factor but its limitation will also depend on resolution that the game is played at; haha, can you even choose this on a mac? I guess at the same time one could consider potential nongaming memory latency performance in macs as well?

[mduell]

Hrm, perhaps I was incorrect and the iMac can run it at CAS2 timings.

Then again, perhaps it's all for naught: Here's an article that benchmarked the G5s memory latency. Twice the latency with RAM of a P4 and about 2.5 times the latency of AMD64. With such a poor memory controller, I really can't see the lower timings doing anything for you.

[coho]

hhhhmmmmmm interesting. right on.

does the powermac use the same chipset & memory controller as the imacs? reason i ask is apparently barefeats.com found this:

"Maybe memory latency speed makes a difference after all. I was doing some testing on two different G5/2.5GHz Power Macs. They are configured identical in every way (8GB RAM, GeForce 6800 Ultra). In fact, they have identical Raptor 10K boot drives in the top factory slot with contents of one cloned to the other. When I ran my Motion 2 "render RAM preview" test, one system ran 8% faster than the other. Why? Well, there is one difference. The faster G5 had CAS 2 memory and the other one had CAS 3. (The CAS 2 memory we used was Patriot PDC2G3200LLK dual channel memory. Frys Electronics carries it, as does Monarch, NewEgg, and ZipZoomFly.)"

i take those results with a grain of salt though as the tests weren't well described and/or results shown and i have no idea what the hell that test even is...whether it's real or synthetic or what.

however, thanks a lot for the article...that does provide insight...and i although i do side with you that barefeats finding does perk the eyebrows a bit.

[coho]

thanks for all the input...

i didn't end up doing the cas 2 bit...just snagged a 1gig stick of ocz and played it safe.

[CanadaRAM]

The iMac G5 2.0 uses a completely different memory subsystem than the PowerMac G5 <Oct 19 2005

The obvious difference is that it doesn't require paired RAM and cannot use Dual channel.

Although the Apple docs say lower latency RAM is supported, they don't say that lower latency is utilized. There has bee no indication that Apple motherboards can adjust to lower latencies a la Intel "PAT"

Thanks
Trevor
CanadaRAM.com