Confused about Mac Pro Ram

jburrows500

macrumors regular
Original poster
Jan 26, 2007
135
0
Hells Kitchen NYC
Looking to add an additonal 4GB to the already 2 512K sticks in a Mac Pro 2.66. Am I better off going 4 1GB or 2 2GB sticks? Also, is there any reason to spend the extra 80 bucks and go for the mac pro certified ram rather than the cheaper apple qualified ram from OWC?

Thanks!
 

MacsAttack

macrumors 6502a
Jul 2, 2006
825
0
Scotland
Looking to add an additonal 4GB to the already 2 512K sticks in a Mac Pro 2.66. Am I better off going 4 1GB or 2 2GB sticks? Also, is there any reason to spend the extra 80 bucks and go for the mac pro certified ram rather than the cheaper apple qualified ram from OWC?

Thanks!
Technically 4 1GB sticks and tossing the 512s would give the optimum memory performance. In reality the difference is going to be negligible just sticking with the the 512s - remember to put the 1GB sticks in slots one and two on each memory board. I would not even consider using 2GB sticks due to the extra price - unless I was planning some major memory upgrade down the line.

Apple or not Apple. Tricky. if (big IF) it is certified as compatible there should be no problems. In theory. :D
 

MacsAttack

macrumors 6502a
Jul 2, 2006
825
0
Scotland
Can you explain why "tossing" the 512's would give the optimum performance?
The way the the memory works on the Map Pro has the memory modules in slots 3 and 4 on each memory riser daisy-chained off of slots 1 and 2. This increases the time required to access memory on slots 3 and 4 and degrades performance. So by retaining those 512s (in slots 3 and 4 of the first memeory riser - as you want to put the 1 GB modules into slots 1 and 2 on each memory riser) you are going to see some drop off in memory performance.

In real life situations the real performance drop is negligible unless you have a memory-intesnive application running. Even then it will not be a disaster. The question is whether you are better off with another GB of memory (to stave off paging which does have a big impact on performance), or best to go for max memory performance by not using the 512s.

Some reading http://www.hardwaresecrets.com/article/266

I also beleive I saw a note that 512 modules are single rank devices, where as 1GB modules (and bigger) use two ranks. Have to dig up a reference. If that is the case, then the bandwidth off those 512s is going to be half normal - another possible hit on performance. I do know when one rank went bad on a 1GB module the hardware cut out the matching rank on the other 1GB module and I found myself with only 3GB of memory until the bad 1GB module was replaced. One advantage of the FB-DIMMs and the server/workstation grade hardware was that my Mac Pro suffered not at all from the faulty memory.

The 512s were a cheep option by Apple (big surprise). Minimum memory in a Mac Pro should be 4 x 1GB. :D


Ahhh.. Found it... http://www.anandtech.com/mac/showdoc.aspx?i=2832
 

Umbongo

macrumors 601
Sep 14, 2006
4,931
54
England
I would not even consider using 2GB sticks due to the extra price - unless I was planning some major memory upgrade down the line.
Most vendors offer 2x2GB cheaper than 4x1Gb, and those that don't are only a few dollars more or not worth bothering with.
 

jburrows500

macrumors regular
Original poster
Jan 26, 2007
135
0
Hells Kitchen NYC
Actually I can sell back the 2 512K for $55 when buying the 1GB sticks. So in the end just go with the 4 sticks of 1GB and call it a day.. Sounds good... Thanks.. much appreciated.
 

sblasl

macrumors 6502a
Apr 25, 2004
844
0
Heber Springs, AR
Thank you for taking the time to provide the explanation and the links, for the first time I think I finally have a grasp of the concept.

The way the the memory works on the Map Pro has the memory modules in slots 3 and 4 on each memory riser daisy-chained off of slots 1 and 2. This increases the time required to access memory on slots 3 and 4 and degrades performance. So by retaining those 512s (in slots 3 and 4 of the first memeory riser - as you want to put the 1 GB modules into slots 1 and 2 on each memory riser) you are going to see some drop off in memory performance.

In real life situations the real performance drop is negligible unless you have a memory-intesnive application running. Even then it will not be a disaster. The question is whether you are better off with another GB of memory (to stave off paging which does have a big impact on performance), or best to go for max memory performance by not using the 512s.

Some reading http://www.hardwaresecrets.com/article/266

I also beleive I saw a note that 512 modules are single rank devices, where as 1GB modules (and bigger) use two ranks. Have to dig up a reference. If that is the case, then the bandwidth off those 512s is going to be half normal - another possible hit on performance. I do know when one rank went bad on a 1GB module the hardware cut out the matching rank on the other 1GB module and I found myself with only 3GB of memory until the bad 1GB module was replaced. One advantage of the FB-DIMMs and the server/workstation grade hardware was that my Mac Pro suffered not at all from the faulty memory.

The 512s were a cheep option by Apple (big surprise). Minimum memory in a Mac Pro should be 4 x 1GB. :D


Ahhh.. Found it... http://www.anandtech.com/mac/showdoc.aspx?i=2832
 

MacsAttack

macrumors 6502a
Jul 2, 2006
825
0
Scotland
Thank you for taking the time to provide the explanation and the links, for the first time I think I finally have a grasp of the concept.
No problem. As I said before, in most real life situations I don't think it makes that much difference. Where the it is most noted is going to be in synthetic benchmarks.

I tend to take benchmarks with a pinch of salt :D All I care about is that my Mac Pro is a very nice fast machine. Now I have the CS3 suite it is even faster for much of my work. By all accounts Leopard is going to make it faster still (going to have to wait a few months yet to see if that is true).