Barefeats Says 12 GB Sweet Spot on octo-core

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Level 1

65 points

Barefeats Says 12 GB Sweet Spot on octo-core

On their performance chart for rendering with After Effects, 12 GB of RAM beat 16. Is this likely to be true on all pro apps? When buying RAM for these machines, should we always think in multiples of 3?

Powermac G5 (late 2005) Dual 2GHZ, Mac OS X (10.5.6), 4.5GB RAM, 2 WD Caviar SE 640 HDs, ATI X1900, 2 Samsung 2343BWX

Posted on Mar 12, 2009 3:56 PM

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Answer 1

Mar 12, 2009 4:24 PM in response to BOBBOBKK

Thats what I have been hearing. I am a little concerned because I have 8GB on the way to me and I have 6GB currently installed. I was told not to fill up the 4'th and 8th slot since it may slow performance (odd). I was told to purchase the extra 4 GB ram and replace all the 6 x 1GB ram sticks that came with my order. I was thinking maybe just going with a

S1: x2GB
S2: x2GB
S3: x1GB
S4: blank
S5: x2GB
S6: x2GB
S7: x1GB
S8: blank

not jacking your thread, but just stating that we are in the same boat

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Answer 2

BOBBOBKK Author

Level 1

65 points

Mar 12, 2009 4:41 PM in response to Chexmix26

I haven't owned a Mac Pro yet, but from what I've seen, I don't get the sense you can as cleanly mix memory sizes as on the old G5. I'm guessing some of the experts will recommend you end up with 6 2GB sticks and install as you've laid out, skipping slot 4.

If your memory is coming from OWC or the like, I imaging they'd refund your any 1 GB sticks, but if it's your original from Apple, it seems there should be a way to sell your 1 GB sticks to a couple people who just want to go from 3 to 6.

Be interesting to try Geekbench or some rendering with your current configuration, then see how the results change when you add the new RAM.

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Answer 3

Duo

Level 2

475 points

Mar 12, 2009 5:20 PM in response to BOBBOBKK

BOBBOBKK wrote:
When buying RAM for these machines, should we always think in multiples of 3?

Absolutely. The new Mac Pros processors have a triple-channel memory interface, and each channel moves at about 8.5GB/sec. This means that if you toss in three same-sized memory modules, you'll get peak memory bandwidth of about 25GB/sec. Add a fourth module, and that module has to share a channel with another module since there are only three channels.

Depending on what kind of work you do, having more memory may provide a greater performance advantage than simply having -faster- memory, but as always, your mileage may vary.

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