Since I’ve gotten the machine a few months ago, I’ve been using the Mac Pro in its standard stock configuration with 2 GB RAM.
But, as I continued to use it and handle multiple applications concurrently, I began to realize that I definitely need to ramp up the available memory on the computer.
So, I went ahead, placed the order, and it arrived today: 2 sticks of 2 GB FB-DIMM, ready to install.
A lot of people have commented about how tricky it is to install RAM into the Mac Pro, but I couldn’t figure out why.
This is what I did:
- I unplugged all of the cables from the Mac Pro unit.
- I placed the Mac Pro unit on its left side (facing it from the front).
- I flipped up the side panel lever. This flat lever is located at the back panel of the unit and is normally flush with the panel, so you need to pop it up and outward. Once it is fully flipped out, the right side panel (facing the Mac Pro from the front) was loosened, so I could lift it up and away. Since the side panel is anchored along the bottom edge (in a sort of metal “lip” or ridge), it was easy to lift up along its top edge first, and then dislodge it from the bottom.
- The RAM compartment is toward the back lower corner of the case, and the two riser boards are clearly visible.
- I pulled each board out, placed them both on the desktop surface.
- Looking at the two riser boards, I could see that each of the two 1 GB FB-DIMMs were socketed into the first DIMM slot.
- I removed the FB-DIMM from the bottom riser board and slotted it into the second DIMM slot on the top riser board.
- I socketed the two new FB-DIMMs into the first and second DIMM slots on the bottom riser board.
- I slotted each of the riser boards back into the RAM compartment in their original orientations.
- I placed the right side panel back into position, and then flipped the side panel lever back to its original position, locking the right side panel into place.
- I brought the Mac Pro unit back up, then plugged all of the cables back in.
Once I got the Mac Pro reassembled, I fired it up, logged in, and brought up the Activity Monitor as some of the startup applications also launched themselves. The screenshot below is what I saw:
Cool, eh?
This is the first time that I recall seeing such a large green pie slice (representing free memory), compared to the rest of the allocation pie. Good times!
The Deal with the Memory Slots
Why did I relocate the 1 GB FB-DIMM from the bottom riser board to the top riser board? And why did I plug the two new 2 GB FB-DIMMs into the bottom riser board?
There’s apparently a specific order that FB-DIMMs must be applied to the two riser boards, based upon these rules (sorry, I’m not actually quoting or paraphrasing from anywhere):
- FB-DIMMs must be applied in pairs to the riser boards;
- If there are only two (2) FB-DIMMs, there should be one in each of the first DIMM slots;
- If there are more than one pair of FB-DIMMs, let’s go with this setup configuration:
- Two (2) pairs: one (1) pair in top riser board’s first and second FB-DIMM slots, and one (1) pair in bottom riser board’s first and second FB-DIMM slots;
- Three (3) pairs: one (1) pair in top riser board’s first and second FB-DIMM slots, one (1) pair in top riser board’s third and fourth FB-DIMM slots, and one (1) pair in bottom riser board’s first and second FB-DIMM slots;
- Four (4) pairs: one (1) pair in top riser board’s first and second FB-DIMM slots, one (1) pair in top riser board’s third and fourth FB-DIMM slots, one (1) pair in bottom riser board’s first and second FB-DIMM slots, and one (1) pair in bottom riser board’s third and fourth FB-DIMM slots.
I strongly recommend that you keep FB-DIMMs from a specific manufacturer paired together, since any performance mismatches may manifest as odd system behavior (and won’t that be a real pain to debug?).
The Deal with the FB-DIMMs
A lot of folks have asked me, “Hey, Steve, I keep seeing different FB-DIMMs being sold. Which should I get for my Mac Pro?”
Well, before you place an order, you need to know which kind of Mac Pro you’re using. The first generation of the Intel Quad-Core based Mac Pros typically use the 667 MHz ECC type modules, while the early 2008 Intel Quad-Core based Mac Pros should use the faster 800 MHz ECC type modules. Using the faster ECC modules in an earlier Mac Pro should be fine, but I’m not sure it’s worth the extra cost– although if that’s all you got on-hand, then go for it!
However: be careful about the heat spreaders on the FB-DIMMs. Apple certification specs of the FB-DIMMs for the Mac Pro are apparently more highly performant than your regular ol’ JEDEC heat dissipation specs. You don’t want to shell out big bucks to get FB-DIMMs with crummy heat spreaders!
Good to Go
Now that I’ve got the extra memory, it’s time to get back to the fun! 
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