Weeks have passed since Apple's announcement of the Mac Pro, and while we wanted to conclude our look at the Mac Pro much earlier, like many Mac Pro users we ran into some serious performance issues under Windows XP.

With the Mac Pro performance issues resolved and some more time with the system under our belts, we're able to bring you the final part in our Mac Pro coverage. This time we're focusing on upgrading the memory and CPUs in the Mac Pro, as well as looking at its performance as a PC running Windows XP.

As a high end Xeon based machine that can run both Mac OS X and Windows XP, the Mac Pro has the potential to be the power user's dream. Today our task is to find out just how upgradable this machine is and how well it runs XP, if it can truly be your only system if you're a Mac and PC user.

FBD Revisited

Thus far the only real downside we've seen to the Mac Pro is its use of Fully Buffered DIMM (FBD). As we mentioned in our initial article discussing the Mac Pro's specifications, the FBD spec calls for a serial interface between memory controller and memory modules, while allowing the chips on the memory modules themselves to be regular mainstream DDR2 devices. A FBD memory controller talks to an AMB (Advanced Memory Buffer) on each memory module, which acts as a translation hub and buffer for all communication between the DDR2 devices on the module and the requests from the memory controller.

The major benefit of FBD is the ability to feature more memory modules per channel (up to 8 per channel), offering greater capacity for high end servers and workstations than even registered DDR2. The downside to FBD is that there is significant overhead and latency introduced by using a packetized interface and using the AMBs to translate from one interface technology to another (FBD to DDR2).

As we mentioned and proved in our previous articles, the number and configuration of FB-DIMMs in your Mac Pro can affect performance. The Intel 5000X chipset in the Mac Pro features two 144-bit FBD branches, each being the width of two FB-DIMMs (effectively giving the chipset four "channels"). Therefore you need at least two FB-DIMMs in the system (the width of a single FBD branch), but ideally you'd need at least four to have a hope of attaining peak bandwidth.

As some of our readers (and Intel) pointed out, the story doesn't just end at needing four FB-DIMMs. The rank of the FB-DIMMs can impact performance as well, and ideally each of your FB-DIMM modules would be dual rank modules. The rank of a DIMM is determined by dividing the width of all of the devices on the module by the width of the module itself. For example, a single rank FB-DIMM would have 9 DDR2 devices each being 8-bits wide. A dual rank FB-DIMM would be composed of 18 DDR2 devices, each still being 8-bits wide. All of our 512MB FB-DIMMs are single rank modules, while our 1GB and 2GB modules are dual rank.

The story doesn't end with rank though. Because of the dedicated read and write lanes between the memory controller and the AMBs on FB-DIMMs, you can be reading from one FB-DIMM while writing to another. So in theory, if you're running an application (or combination of applications) that have a lot of concurrent reads and writes going on you could stand to benefit from having more than one FB-DIMM per channel.

Based on all of the above information, it would seem like your best bet is to stick as many dual rank FB-DIMMs as you can afford in your system, and if that were the case then we'd be able to move on from here. Unfortunately it's not, because as we mentioned in previous articles, the more FB-DIMMs you have in your system, the higher access latencies will be to those additional FB-DIMMs.

What we then end up with is a tradeoff between more bandwidth and higher latency, so which route do you take? We've done a lot of testing and most of our tests seem to favor the four dual-rank FB-DIMM module configuration, but the number/configuration of modules really depends on your particular needs. We're still testing to figure out what the tangible real world performance differences are between the multitude of memory configurations, but for now just know that if you need maximum bandwidth you'll want 8 dual rank FB-DIMMs, but if you want lower latency you'll want fewer modules. Whether or not you'll see a performance difference will depend mostly on the application(s) you're running.

Third Party Memory Modules
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  • Calin - Wednesday, September 13, 2006 - link

    I suppose this appeared in some service pack. I've thought that XP is somehow physically limited in using just two apparent processors (one processors with HyperThreading, one dual core processor and so on). I was not referring to the licensing limitation (which I know very well - Microsoft counts one processor package as processor, no matter how many cores inside).
    So, will Windows XP use all the 8 cores in a 2 socket quad core configuration?
  • JarredWalton - Wednesday, September 13, 2006 - link

    I don't have a 2S quad core setup (damn!), but I do know that XP Home works fine on dual core with SP2. Heck, the PC Club I reviewed a couple weeks back was Core 2 Duo with XP Home. I actually talked with a Microsoft rep a year ago and he said XP worked based on sockets, so basically there's just code to prevent XP from using more than a certain number of sockets.

    It's rather if you ask me, and I think MS should forget about what hardware is being used and simply sell/license the software, but that's one way they like to make money. "Want a 4 socket server? Oh, you'll have to pay thousands of dollars for the OS now. It's no different from the $150 OS, except we flipped a switch to support more sockets."
  • blwest - Tuesday, September 12, 2006 - link

    This is flawed in many ways.

    Intel Xeon 5150 2.66Ghz $729 ***times two***, the mac pro has two!!!

    3x 250GB Western Digital in raid 5 $65 each = $195
    **current asking price is 70** $240

    Pionere 110D = $50

    7900GT $260
    **$290** for a decent model

    2x 1GBx2 OCZ PC2-5300 $200 each = $400
    **the 5000 series mainboards all run fbdimms, must buy them $109 each for 512 meg sticks***

    TYAN S5370G2NR-RS Dual Socket 771 Intel 5000V SSI CEB Server Motherboard $319 supports 16GB ram

    **where's your price on this??*** $320

    Cool Master Stacker $154
    *crappy case compared to apple**

    Rosewill RP600V2-S-SL 600W SLI Ready $70
    **can you go any cheaper? the apple has a 1000 watt unit**

    Linux OS , Microsoft Windows XP Professional X64 Edition Single Pack $139

    $2316 **NOT**

    Given 2x 512 sticks and 2 processors, a little better video card and his other components, you get $2800+/-. If you include a 1000 watt powersupply add at least 100 dollars. How much time will it take you to build this system? What is your time worth? Like the other poster said, add firewire, sound, keyboard, mouse and a 1 year warranty to the whole system. I threw those items in a cart at newegg and we're also looking at another 75+ in shipping costs.
  • Anand Lal Shimpi - Tuesday, September 12, 2006 - link

    You actually need two Xeon 5150 processors, since the Mac Pro comes with two in its $2499 configuration; therefore you need to add another $729 to your second configuration. As surprising as it may be, the Mac Pro is actually a pretty good buy for the hardware you get, I know it shocked me when I actually calculated it out.

    Take care,

  • don42 - Sunday, March 21, 2010 - link

    I know that myself who has been dealing with pc\s windows(microsoft) and the whole 9 yards is just sick of it. My first computer was a Vic 20, with a cassette tape for external memory, I never did go the commodore 64 route I was too busy working. My next computer was an Amiga 500, at that time there was nothing that could come even near that thing.....it was so good I sprung for an Amiga 2000, that was the best of the best at that time.....I have always had a leaning towards graphics and photography....at that time there was Deluxe Paint from EA....that was before scanners, there was something called Digiview where one could bring digital images into their system by using a security camera with a rgb wheel that was turned.
    I am sure someone is reading this that went through the torment of those. But that Amiga was so far ahead of anything else that I'll end this now. Then I went to PC and now even with windows 7 still look back on that amiga and shake my head. I still have a huge collection of the old amiga mod. files...8 tracks of total genius on some of them.
    Now.....that brings to why I am writing this huge dialogue......I am sitting on a precipice waiting to be pushed over the edge and falling into the world of MAC. One hates to leave what one is familiar with, but I find myself drooling when I look at those new mac pros with the intel nehelams in them. I actually was on the mac store and went as far on ordering until the last few digits of my VISA. Has anyone on here taken that plunge?
    Also can one add a second CPU to a quad core at a future date?
  • Questar - Tuesday, September 12, 2006 - link

    Now include building it, warranty, support, sound card, firewire, software.
  • motoxpress - Tuesday, September 12, 2006 - link

    Clearly you have not priced out an equivilant system. Even at Newegg prices, you can't touch the MacPro for price. The whole "Macs are too expensive" arguement is tired, outdated and false.

  • JeffDM - Sunday, October 8, 2006 - link

    Clearly you have not priced out an equivilant system. Even at Newegg prices, you can't touch the MacPro for price. The whole "Macs are too expensive" arguement is tired, outdated and false.

    It really depends. It is false if you take a very restricted view of computers and that you don't regard flexibility to have a value in the consumer markets. The Mac Pro isn't really helping the argument because it's a workstation and as such the comparison is other workstations. As such, comparing it to an equivalent computer isn't going to win much because very few people are buying workstations, a relatively obscure type of computer, making it not a relevant product or relevant comparison for most people.

    Heck, the Mac Pro isn't even that comparable to the Dell Precision 690, which Apple compared it against. The Mac Pro offers only half the memory slots of a comparable Dell. The Mac Pro uses a consumer video card for all but the top end, the Dell Precision video cards are all Quadro units. The level of stock support isn't the same either. Dell offers three years of on-site warranty support standard, Apple charges extra for three years and it's not on-site.

    I even found a Core Duo-based 17" Toshiba notebook at Sam's Club for $1200. Apple's base price for a 17" is $2800. Granted, the Apple unit does have several features that aren't found on the Toshiba, but I think it's tough to argue that those extra features are worth the extra $1600, especially when you can buy two of the 17" Toshibas with money to spare for more upgrades, for the cost of one Apple 17". You could have an entire redundant machine or money saved for one. For the price of the Apple, I think they should either offer on-the-spot replacement or a loaner machine if the original needs repairs, that's what I'd expect of support for a pro machine, particularly at those price points. As far as I'm aware, they don't offer that level of support.

    Don't get me wrong, I do like Macs, I own a couple, but I don't like the specious reasoning used to argue for or against them. It's very tough to make a reasonably valid comparison to Windows units because Apple only offers three consumer computer models (Mac Book, mini & iMac), and two of those are oddities in terms of form factor.
  • msva124 - Tuesday, September 12, 2006 - link

    What Apple craze?
  • robvoigt - Wednesday, August 25, 2010 - link

    I know it has been a while since this article on upgrading the 2 Ghz Mac Pro, but I'm finally getting around to it. I have some software that says "best run with 3Ghz processor or faster".

    So I am looking for some encouragement to try this process but, more importantly, some hard facts about processors that a user has tried... and found successful. Anybody out there want to recommend a specific processor that they know works?

    My vitals...
    Mod: A1186 EMC No:21'3 100-120V
    MAC PRO/2.0QX/2X512/7300OT/160SD
    Ser No: G86322MRUPZ

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