Can adding more memory slow down my Mac Pro?

Xbench is highly arguably as a usable benchmark utility to begin with.

It is much more important that you have sufficient memory for your usage-pattern.

Barefeets is not the only one to report this. I installed 4x2GBs and pulled my stock 2x1GBs for this very reason (see auction in signature).

You can etiher just pull your 2x1GBs or order two more 2x1GBs and install a total of 12GBs. That should perform very well, as long as groups of 4 FB-DIMMS are matched.

netdog said:

You can etiher just pull your 2x1GBs or order two more 2x1GBs and install a total of 12GBs. That should perform very well, as long as groups of 4 FB-DIMMS are matched.

Click to expand...

Glad you mentioned this... I was going to order 2x4GB to make 10GB RAM for future expandability. Should I order the 4x2GB instead?

In theory yes, your best performance will be with matched memory. However, the chances that you'd notice a real-world difference in normal use are pretty small IME.

Remember: there's lies, damn lies and then there's benchmarks

tersono said:

In theory yes, your best performance will be with matched memory. However, the chances that you'd notice a real-world difference in normal use are pretty small IME.

Click to expand...

In your experience?

Which Mac Pro are you using and what memory configs have you used for a prolonged period to give this assertion some weight?

This memory issue only applies to the Mac Pro. MacBooks have their own issues with matched sticks because of the shared graphics RAM. MBPs really don't care.

Every benchmark test I have read regarding the Mac Pro that addresses the issue of how to configure memory has found in tests that there is quite a difference.

ErikAndre said:

Glad you mentioned this... I was going to order 2x4GB to make 10GB RAM for future expandability. Should I order the 4x2GB instead?

Click to expand...

That's what I chose to do. Yes. Of course, you could also order 4x4GB sticks.

As mentioned earlier, you could also by two more 1GB sticks for a total of 12GB (with the 4x2GB sticks installed).

netdog said:

In your experience?

Which Mac Pro are you using and what memory configs have you used for a prolonged period to give this assertion some weight?

This memory issue only applies to the Mac Pro. MacBooks have their own issues with matched sticks because of the shared graphics RAM. MBPs really don't care.

Every benchmark test I have read regarding the Mac Pro that addresses the issue of how to configure memory has found in tests that there is quite a difference.

Click to expand...

Which benchmarks? The only two I have seen relating to the Mac Pro were from anandtech and barefeats and both conclude that it doesn't much matter for real world performance.

barefeats said:

DUAL CHANNEL vs QUAD CHANNEL
In order to get the full benefit of the Mac Pro's 256 bit memory data path, you'll want to populate both memory riser cards, each with at least one matched pair. If you put your memory on only one riser, you are dropping from quad channel to dual channel mode. See Apple's Mac Pro memory notes for more this.

Does this translate into faster real world speed? Not always. Though the Xbench memory fill rate test showed a 34% gain, it doesn't necessarily translate to faster application speeds. We ran some typical tests from our suite of real world tests (iMovie render effect, Final Cut Pro render clip, Cinebench CPU render, Motion render RAM preview, iMaginator Core Image morph). None of them showed any gains from Quad Channel mode.

Anandtech did some testing with real world apps using dual and quad channel memory configurations, too. Of their 15 real world tests, only 2 showed any gains from Quad channel configuration.

Click to expand...

netdog said:

Barefeets is not the only one to report this. I installed 4x2GBs and pulled my stock 2x1GBs for this very reason (see auction in signature).

Click to expand...

ooooooh.
/clicks "watch this item"

Ok I'll bite...

Like so many people I ordered 2-4 of the 2gb dimms and plan to add it to the stock 2. However I currently have on order 2x2gb of OWC certified, and 2x2gb of RAMJET (diversifying my chances of getting it with the computer). Could the brands minute differences be a factor if I yanked the stock 2gb and just used this batch or should I cancel the RAMJET order and get in the back of the line for more owc RAM. What is the main factor in this performance difference. I'm assuming its the size of the module. Help QUICK I need to act fast!

Answer..

I emailed Rob-Art at Barefeet and posed my question about mixing brands to him and he came back (quite quickly) with this answer.

You'll want to check to see if the RAMJET memory has,
a) CAS 5-5-5 rating and,
b) Apple certified rating, and
c) Apple approved heat sink

If all the above is true, they should play nice with the OWC memory.

Lumpydog said:

All:

I just read this article: http://www.barefeats.com/harper3.html

From reading it, my interpretation is that I may have actually slowed down my new Mac Pro by adding memory...

I purchased an additional 4GB of Ram from OWC - Two x 2GB sticks. I placed the two new sticks in the top riser (4GB) and I placed the two Apple/factory shipped 1GB sticks in the bottom riser (2GB) for a total of 6GB of memory.

The article states: "Some of you just want to buy two 2GB FB-DIMMs to add to the two factory 1GB FB-DIMMs for a total of 6GB. That configuration will slow you down. Don't do it. Again, the BEST performance setup is eight matched FB-DIMMs. The second best is four matched FB-DIMMs."

Should I purchase additional Two x 2GB sticks so I have 4 matched FB-DIMMS? - Two x 2GB on the top riser and Two x 2 GB on he bottom riser?

According to the barefeats article, I could still use the original 1GB sticks in the top riser slots 3 and 4 without slowing things down... For a total of 10GB

Lumpy

Click to expand...

This brings to mind the saying: "There are 3 types of lies - lies, damn lies, and statistics."

The key question is slows you down RELATIVE TO WHAT? On a pure memory test, you will have a speed hit relative to the optimal configuration they tested. But in real world use, where memory speed is usually not the bottleneck, a minor speed hit in memory is NOTHING compared to the OS having to cache something to the hard drive due to lack of memory. Caching memory is a HUGE speed hit.

So back to the question - if you can only afford 4 GB of after market RAM, and you end up with 2 x 2 GB sticks combined with the stock 2 x 1 GB, the system will run MUCH faster with this 6 GB configuration than leaving out the stock RAM and running with 4 GB.

And even putting in 8 GB (4 x 2), the system will run faster in real use when you leave in the odd pair of stock RAM to end up with 10 GB. (Barefeats even tells you how to properly configure this 10 GB option at the bottom of the artlicel you linked to.

netdog said:

That's what I chose to do. Yes. Of course, you could also order 4x4GB sticks.

As mentioned earlier, you could also by two more 1GB sticks for a total of 12GB (with the 4x2GB sticks installed).

Click to expand...

This now has got me thinking and a bit paranoid... what slots do i place these pupplies in and in what bays? Maybe like this?

Bay 1
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty

Slot 2
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty


or....

ErikAndre said:

This now has got me thinking and a bit paranoid... what slots do i place these pupplies in and in what bays? Maybe like this?

Bay 1
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty

Slot 2
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty


or....

Click to expand...

my guess is:
Riser 1
2
2
1
1

riser 2
2
2
0
0

For best performance, you should get paired doubles. So each ram module should be the same size and the total number should be a multiple of 2. So 2x1, 4x1, 4x2 etc. If you don't do this, the speed penalty may not be noticeable, but if you have a complete mix, it may be significant.

Having said this, im still going to have 2x2 and 2x1 in my mac pro....

rockinrocker said:

my guess is:
Riser 1
2
2
1
1

riser 2
2
2
0
0

Click to expand...

I believe this is what the barefeats article says to do.

ErikAndre said:

This now has got me thinking and a bit paranoid... what slots do i place these pupplies in and in what bays? Maybe like this?

Bay 1
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty

Slot 2
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty


or....

Click to expand...

I think that's right. As mentioned before, better if you fill both slot 4s with 1gb pieces or leave slot 3s empty.

I was going to ask about this as well...When I just had 2 gigs in there, the machine booted in like 30 seconds, but as soon as I put the extra 4 gigs in (2x2), now it takes over a minute to boot up (uh, not that I'm probably ever gonna have to reboot this thing much...hehe)

Ok, so as soon as I can, I'll grab 2 more 2 gig sticks to make it 8...

Netdog: If you can continue to use the extra 2 gigs without slowing down, why wouldn't you?

Also, I thought I remembered reading somewhere that in order for Applecare to remain valid, you have to at least keep the Apple RAM and reinstall it when you bring it in to be serviced...

-Bryan

rockinrocker said:

my guess is:
Riser 1
2
2
1
1

riser 2
2
2
0
0

Click to expand...

Jupeman said:

I believe this is what the barefeats article says to do.

Click to expand...

It also happens to be what Apple recommends in the little brochure they ship with the MP. The ONLY configuration they show with non-matched pairs is the way they ship a standard 2GB config (1 stick in slot 1 of each riser). I have 10GB in my machine installed as shown above.

ErikAndre said:

This now has got me thinking and a bit paranoid... what slots do i place these pupplies in and in what bays? Maybe like this?

Bay 1
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty

Slot 2
Slot 1: 2gb
Slot 2: 2gb
Slot 3: 1gb
Slot 4: Empty


or....

Click to expand...

While I think this was the recommended installation in the 2007 MP, I believe the barefeats post said that the early 2008 MP would only show RAM installed in this manner as 8 GB. If you put the 1GB in Slots 3 and 4, then the MP recognizes the full 10 GB.

Still sort of sucks tho... i wanted to buy 2x4Gb sticks (move to 10Gb) so I could expand later, but in order to satisfy this article, i have to buy 4x4Gb (which will tap the bank). Looks like I'm stuck with getting 4x2Gb and clutter the slots.

ErikAndre said:

Still sort of sucks tho... i wanted to buy 2x4Gb sticks (move to 10Gb) so I could expand later, but in order to satisfy this article, i have to buy 4x4Gb (which will tap the bank). Looks like I'm stuck with getting 4x2Gb and clutter the slots.

Click to expand...

It might bust the bank, but you gotta admit...4x4 would be pretty sweet.

netdog said:

It might bust the bank, but you gotta admit...4x4 would be pretty sweet.

Click to expand...

Indeed... but the bank has been very generous this year (with a 3.0MP, 8800GT and a 8GB upgrade)... i have plenty of leash here, but i don't want to push it, if you know what i mean.

ErikAndre said:

Indeed... but the bank has been very generous this year (with a 3.0MP, 8800GT and a 8GB upgrade)... i have plenty of leash here, but i don't want to push it, if you know what i mean.

Click to expand...

Sounds like the bank has a whip.

netdog said:

I think that's right. As mentioned before, better if you fill both slot 4s with 1gb pieces or leave slot 3s empty.

Click to expand...

Stop giving advice because you have no idea what you're talking about.