The Mac Pro overview, part 2: hard drives and memory upgrades

Posted by Dennis Sellers Aug 21, 2006 at 11:10pm

Yesterday we started our multi-part review/look at the Mac Pro, which was announced on Aug. 7. Yesterday we looked at the case; today we’ll look at the Mac Pro’s new type of memory—and how it and extra hard drives are installed. There’s both good and bad news (mostly good).

The Mac Pro can hold four Serial ATA (SATA) drives, twice as many as its PowerPC G5 predecessor. Installing a new drive is simple. You just slide out an empty drive housing, attach a SATA drive to it with four included screws, and slide the drive back into the computer.
The Mac Pro ships with four housings, even if you purchase it with one internal drive. The drives attach directly to the system’s motherboard, so there’s little messing around with cables. The housings are elegantly designed, and the drives slide smoothly into place. To install a hard drive, pull out the carrier and housing, lay it on top of the hard drive, attach the drive with the four screws already in the carrier, and slide it into the Mac Pro.

Then there’s the RAM. Unlike any other Mac, the Mac Pro uses Fully Buffered DIMMS (or FB-DIMMs), an Intel-developed format the offers high memory performance. But it ain’t cheap. In fact, it’s about twice as much (if not more) costly than other RAM. That’s because each FB-DIMM has its own memory controller onboard. This means extra heat, so each FB-DIMM comes with its own heat sink, adding to their cost. Still, you can max out your Mac Pro with 16GB of RAM if you have a reasonable credit card limit or take out a bank loan.

What’s more, FB-DIMMs must be installed in pairs. For the best performance, you’ll need to have at least two pairs of FB-DIMMs installed in your Mac Pro. Installing the RAM is easy, even easier than completing the task on the Power Mac G5, which was itself reasonably simple.
Using a “riser system,” the Mac Pro has two RAM carrier cards, each with four slots. To install RAM, slide the card out, place it on a hard, flat surface (the card has plastic feet on its back side), and insert your new FB-DIMMs. Then reinsert the card.

There are eight slots in all, four on each card. The slots are spaced wider than usual, thanks to the heat sinks that Apple says are there to “ensure that the fans run at the proper speed to maintain the optimal temperature and ensure acoustic performance.” FB-DIMMs with conventionally sized heatsinks will work in the Mac Pro, although Apple recommends Apple-approved heatsinks “for optimum performance and acoustics.” Right now that seems to include memory ordered from Apple or from OWC.

OWC Mac Pro upgrade kits are comprised of matched pairs of FB-DIMM modules and include the use of Apple Qualified Head Spreaders. They’re priced from US$559 and offered in matched sets comprised of 1GB or 2GB modules available in kits from 2GBs and up to 16GBs\l. A cash-back rebate of up to $350 per set is available from OWC for the trade-in of Apple factory memory. The Intel-based Mac Pro Quad Xeon requires memory be installed in the Matched Sets, as is offered by OWC. For details go here.

Also, OWC has posted a [url=http://eshop.macsales.com/shop/memory/Mac-Pro-Memory]video[/ur] for installing RAM on a Mac Pro, as well as videos for the optical bay and hard drives. You can get less expensive FB-DIMM, but some of it comes with no heatsink, which, as I understand it, could be a problem in the long run, so proceed with caution. Part of it is also to do with the DRAM used and quality control. You see, that ABM chip gets very hot. The ABM is rated for up to 125C operation. Top tier DRAM though is rated for only 70C—making the thermal application very important since otherwise the ABM literally fries out DRAM that’s near to it.

Traditionally, data lines from the memory controller have to be connected to data lines in every DRAM module. As memory width, as well as access speed, increases, the signal degrades at the interface of the bus and the device. This limits the speed and/or the memory density. FB-DIMMs take a different approach to solve this problem, as explained at Wikipedia.Fully Buffered DIMM architecture introduces an Advanced Memory Buffer (AMB) between the memory controller and the memory module. Unlike the parallel bus architecture of traditional DRAMs, a FB-DIMM has a serial interface between the memory controller and the AMB. This enables an increase to the width of the memory without increasing the pin count of the memory controller beyond a feasible level. With this architecture, the memory controller doesn’t write to the memory module directly; instead, it’s done via the AMB. The AMB can compensate for signal deterioration by buffering and resending the signal. In addition, the AMB can also offer error correction, without posing any overhead on the processor or the memory controller. There’s an article at Bare Feats about the new memory that’s worth your time.

Tomorrow we’ll look at the Mac Pro’s standard video card and upgrade options.

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