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
POST A COMMENT

70 Comments

View All Comments

  • newrigel - Monday, September 01, 2008 - link

    I own both and my mac smokes my PC's and I have the latest and greatest PC's made!!!
    For audio, the Mac rules because I can audition an audio file within the file hierarchy and with windows I can't so...
    Reply
  • greylica - Tuesday, September 12, 2006 - link

    I Guess Fully Buffered Dimms, with a new controler that can cut latencies will do it just fine, and sooner or later we will have a situation where every part of theh computer can achieve higher performances by a number of serialized and specialized controllers, memory then can serve as a memory controler/memory module and report to the system as well as aa SCSI device. Remember in teh past years you can buy an external memory controler that serve as a SCSI card, with special functions.
    May intel will be giving you to the future in this way cause chipsets, specially north bridge with all those functions into the same package, and the nightmare to be pinning dedicated MTRR to adress memory sets into the same motherboard with only three layers, and diverse other issues caused by cost limits in this type of config with much more RAM.
    May Intel can be wrong too, AMD haves a controller dedicated into every processor with NUMA ( Non Uniform Memory architeture ), but again we have a pin count to make a hell with Growth of RAM in the computer world if we use memory like we are using until now.
    We have two sides of the story now, and, in the two cases, we have to have a dedicated controller to count memory and acess it, may be a dedicated controller with numa, or a dedicated controller over a north bridge that is nearly the same thing, except the aproaches. A Nort Bridge that servers every processor or processors that serves each other passing data as needed on Numa.

    Every memory now will be serialized to achieve the growth of the use, and we will use more and more RAM.

    FB Dimms not scares me, what scares me is that the other manufacturers will delay to start using it.

    And I really prefer Registered ECC or FB Dimms as they are reliable, did you use memtest in every memory that you have ? I use.
    One bit error and I turn back to guarantee. I don´t have time to waste with a defect that every time appears different...

    Good Vibes.
    Reply
  • vailr - Tuesday, September 12, 2006 - link

    Isn't there a bios size difference between Mac vs. PC video cards? The Mac cards use 512 K bios chips, while PC cards have only 256 K. Thus, trying to flash a PC video card with a Mac version bios won't work. The extra 256K has something to do the video card's compatability with the EFI bios.
    Another question: PowerPC Macs could boot from an external firewire HD (but could not boot from USB). PC's can boot from external USB HD's, but not from firewire. What's the external bootable HD situation with the Mac Pro? Is the Mac Pro's EFI bios configurable? Haven't seen any screenshots of the Mac Pro's EFI bios setup.
    Reply
  • JarredWalton - Tuesday, September 12, 2006 - link

    I believe some PC cards will have the same size BIOS chips, but if not you need to get a hacked BIOS where someone has stripped out some extras to fit a 512K BIOS into 256K. I think I've heard of it being done, but honestly I haven't ever tried it - I don't have any Macs, unlike Anand, Derek, and a couple others. Reply
  • waamatt - Tuesday, September 12, 2006 - link

    I think the high speed DDR2 + Core 2 Duo combo outperforming certain tasks on an FB-DIMM and Xeon (Dual Core) system is precisely the reason we won't see a plain ol' Mac tower anytime soon. I'd love one, but if something you want to do can be done better on it than on their pricier system, they'd just want you to buy an iMac. Hopefully advancements will be made with the whole FB-DIMM system to allow for lower latency and generally better performance, sooner than later.

    The GPU thing is a bit annoying with Macs, but it IS getting better. The number of options is growing, and the ability to keep up with new/relatively new cards is definitely better than it was, say, 3-5 years ago.

    That said, I wouldn't consider buying a Mac Pro until about the third revision as I'd like to see FB-DIMMs improved and better clock speeds on quad core processors. Plus, that sort of provides time to work out any other minor kinks in the system.

    Over all, this trio of Mac Pro articles was excellent for the way it discusses the technologies used as opposed to just going, "Ooh, aah, pretty Apple!" (Actually, does anyone other than Apple do that?)
    Reply
  • MonkeyPaw - Tuesday, September 12, 2006 - link

    I wonder how well Vista RC1 would run on the MacPro? Reply
  • blwest - Tuesday, September 12, 2006 - link

    Anand,

    I've been reading your site for years. This article was excellent in pointing out the limitations and strengths of FB-Diimms. I'm coming to a point in my life where I'm still very interested in technology, performance and the technical aspect of things.

    However, do not have the time to research individual parts, etc like I used to back in my college days. I think Apple produces a quality product with an appreciation for attention to detail. This article helps us to understand the technology, how it works and how to DIY upgrade the Mac. FWIW, the Apple case is even much higher quality than my $400 Lian-Li PC setup I run my server (linux) on. Apple has finally given us weekend warriors a sytsem to tinker with and upgrade!

    As always I take information from your article and use deductive reasoning to extrapolate what is and isn't applicable to my situation.

    I agree with the previous poster's comment, Apple sells this system well below what you can piece it together on your own--or what Dell sells.

    The final point I'd like to make is that this is a Professional system, not a gaming system. If you're into creativity, using your computer for pictures, movies, online chatting or web development--the mac's for you. If you're into running MS Office, business apps or games, then XP is for you. I no longer have time for games and prefer to use my home system for saving my family memories, communicating with friends/family and not having to pop my case open to clear my cmos in order to accomplish these things.

    Thanks again for all that you do.

    Reply
  • yacoub - Tuesday, September 12, 2006 - link

    Is that Motley Crue - S.O.S. I hear playing?

    It's the saaaame old, It's the saaaame old situa-a-tion...

    Gaming: Windows PC, video work: Mac.
    Reply
  • greylica - Tuesday, September 12, 2006 - link

    Yesss, the same old situation, Mac for vídeos and a PC for games, Microsoft and others when the Mac was not X86 always tried to put them on the Vídeo maker market, 2000 and XP takes place in an big users base, but they are always telling you the same thing, use a Mac. Windows is limited.
    I´m the Ceo of Grey Silica Brazil. I´m specialized to work with Blender (A Now GNU program to 3D content Creation for films and presentations ), and tested every possibility of those "dream machines" when they are on the market with their S.O.s. All I have experienced is that windows XP is a shame compared to 2000, 98 is a never think software for 3D services, although I have to use some times in 1999. Some capture cards simply doesn´t function on NT or even 2000 because of drivers.
    But leaving this question I Guess when 2000 was launched Microsoft did a very Good O.S.
    XP introduces spywares to the market, as Hackers wanted too to sell information to others to make money, the same thing as Microsoft does with their partners. You register your software to activate it and a Database Knows what machine you have, the memory you are using, the programs you have installed, the VGA card, etc, etc.
    Windows XP takes this information to sell to others and everybody knows that, course, you have to accept to use... Linux is still on the road, money mekes this world, pressure to not gave information to linuxers is a bad, bad thing.
    Well, Win 2000 now takes those information too, when you download Windows Update services, and WGA have to be installed to 2000 too in some cases. OK. When needed. But it happens now, and not when 2000 was launched. 2000 is not a bad example for hackers.
    If I am a hacker, course that I will think in the same way, I will create my own .net passport with the information hacked or stolen from them, if they buy Nvídia, tell my partners " Buy Nvídia, they sell well !".
    It´s a PC world created, not a MAC bad example. My admiration for the Mac world too, like Anand, Mac not created this monsters of vírus and spywares, they did not do this bad example to humanity collecting data in this way and serving as a sample to hackers.
    The other major problem is limiting the users, 64 Bit can use 128GB of RAM or more, Vista is 64 GB caped, and blogs are saying 4GB is for the kernell. UAU !!!
    OMG !!! 4GB for the kernell, astounting.
    Why they want to limt the users, when Mac and Linux are on the other road ?
    Obvious... To sell other S.O.
    Windows will be a Game console System in few years this way, not an S.O. great to work like they ever swear to you.
    Compare XP to 2000... They can do exactly the sa thing, but 2000 does it better and faster, complimentary software do not leave you to oblivion, Who needs I.E. 7 ehwn Firefox is better and oppen ? Who needs simple compacted folder included in explorer when 7-zip opens more files than you can imagine ?
    Who need My pictures when corel snapfire is better ?

    2000 is the best windows. Fill him with the right software and you will have the most powerfull windows ever.

    Leave MAC for MAC OS-X or Linux, when they gave you hardware that is capable of 128 GB, the OS will achieve this and will not limit you. Will you use Vista knowing this ?
    Reply
  • bobsmith1492 - Tuesday, September 12, 2006 - link

    Well, thank you for the enlightenment. I will never use Vista now that I know I cannot use more than 64GB of RAM. Reply

Log in

Don't have an account? Sign up now