How do I install memory on the Mac Pro?

Put your 4 x 2 Gb RAM in Riser A - slots A1 A2 and Riser B slots B1 B2

 

Other World Computing has a video on their site that explains RAM placement in the Mac Pro here: http://eshop.macsales.com/shop/memory/Mac-Pro-Memory

 

Assuming the memory positioning hasn't changed since the original Mac Pros, the best config would be:

Riser A: A1, A2 - 2GB each; A3, A4: 1GB each
Riser B: B1, B2 - 2GB each

The order of install is:

Riser A1/2, Riser B1/2, Riser A3/4, Riser B3/4. It's probably better to have the larger DIMMs in slots 1 and 2 of each riser, rather than 3 and 4, but there is really no requirement for this. You do always want to fill slots 1 and 2 before 3 and 4, though I'm not sure if anything will break if you don't. Most systems (and I assume Mac Pros are included) don't need DIMMs installed in a specific order, they just prefer it for optimal performance.

The reason you want to fill each riser with 2 DIMMs rather than one riser with 4 DIMMs is because each riser is for one of the CPUs. To access Riser A from CPU B, CPU B has to go via CPU A's bus system, thus causing additional latency on memory access. Data for each CPU in a multithreaded application will be placed on the appropriate Riser's ram for faster access, so you'll get significantly better overall performance by alternating risers. Also, since CPU A will get load before CPU B, if you have odd quantities of memory you'll generally want to put the extra on Riser A.

While not for your situation, I think about the only exception to placing a larger DIMM on the first Riser would be if you had 4x1GB and 2x2GB memory sets. Then you'll want to keep the 4x1GB on the same riser. The choice of which riser probably doesn't matter as much in this case. However, 1GB DIMMs usually have slightly faster internal addressing timings than 2GB DIMMs, so I'd put the 4x1GB on Riser A and the 2x2GB on Riser B. Generally you want to balance memory quantity for each riser, not the number of DIMMs (beyond being in pairs). Thus if you have 2x1gb, 2x2gb, and 2x4gb, put the 2x4 on Riser A and the other 4 on Riser B so you have 8GBs optimally for CPU A and 6GBs optimally for CPU B. While this isn't an "endorsed" configuration by apple (because you filled out Riser B before Riser A), it should be more efficient than the "endorsed" configuration.

 

From reading the user guide of the new MP, I'd do this:
Take both standard 1GB modules out of each riser and put them aside. Install your four new 2GB sticks first, with 2 sticks in Riser A, slots 1 & 2, and 2 sticks in Riser B, slots 1 & 2. Then place your original 1GB sticks in Riser A, slots 3 & 4. That way you have four matched sticks in slot 1 and 2 of both risers.

 

This thread seems relevant to what im looking to do temporarily. What sounds like the best option?

Just ordered 4x 4g sticks from crucial, however only 2 arrived and the rest are on backorder. Currently have 4x 512s with 2 installed on each riser.

Originally was going to just pull the 512s and just run the new sticks to make 16g which should be a nice improvement. Since I have no idea when they'll be back in stock should I just run both 4g sticks together on the first riser, or put one in each riser? Or I could run both 4g sticks on riser a, then 2x 512s in the remaining slots in riser a, and 2 of them on riser b while im waiting for the rest of my ram to arrive. Or just put 1 4g chip in each riser and wait it out with 8g? Not that 8 would be all that bad for the time being. Thoughts...

 

Last time i had a computer guy replace a few of my items he put my memory in weird due to the innards being intell:

he put everyt memory stick in an odd slot, such as 1,3,5,7 it was weird and i had to show him how to put them in, but now i have this set up:

riser a= 2 1gig apple memory sticks.
riser b= 2 4gig crucila memory sticks

does it matter if i put the two 4 gigs on riser a or b with the apple 1 gig sticks on the opposite card?


what i mean is would i see any benefits to putting the crucial 4 gig sticks on riser a as opposed to b?

 

Hehe... When I upgraded mine back then, it was a little confusing cause my memory was fairly fussy. Think I had to play about to pursued the system to see all modules but now all my slots are populated and Apple's supplied modules are in the box.

The supplied manual has a nice illustration as to how you should install your RAM, think it's on page 21 or 22.