Why PCI-X instead of PCI-E on PowerMac G5??

Discussion in 'Macintosh Computers' started by msharp, Feb 18, 2005.

  1. macrumors regular


    Jul 10, 2004
    There are some new graphic cards using PCI-E and seems this is a trend. However, why are there only PCI-X slots present on PowerMac G5 but not PCI-E slots?

    I mean, what's the advantage of PCI-X compared to PCI-E? Will the PCI-X tech be useless in the future and PCI-E acts as the mainstream?

    Thanks for my ignorance.
  2. Moderator emeritus


    Jul 24, 2002
    Mostly because the PowerMac logic board controller is a little old now and does not support PCI-E. I'd expect the next speed bump to change this as top of the range graphics cards are moving to PCI-E.
  3. macrumors regular

    Jan 26, 2004
    PCIe is the way of the future. It's designed to replace AGP (graphics cards), PCI (TV cards, etc) and PCI-X (RAID controllers, high-speed Ethernet, etc). Bigger, better, faster, more, etc, etc, etc.
  4. macrumors 68030


    Dec 30, 2004
    The reason is becsue when apple came up with the PM there was no PCIe but I bet that it will come soon ;)
  5. macrumors G5

    Sun Baked

    May 19, 2002
    PCI-X and PCI-X 2.0 are backward compatible with 3.3V PCI slots -- so you don't have to ditch the PCI cards you have.

    Plus it allowed some of the companies with a vested interest in Macs to easily transition to the new machines.

    If Apple had included PCIe, people who needed to use cards would have had to wait years before making the switch -- since SCSI, audio, video, etc. were not there in the quantity that they needed.


    So expect the next PowerMac to include PCIe video and 3 PCI-X 2.0 expansion slots -- and an outside chance of 2 (or 3) PCI-X 2.0 slots and one PCIe expansion slot.
  6. macrumors 68020


    Jun 18, 2003
    PCIe wasn't mature enough when the PM G5 was spec'ed over 2 years ago. Even now, it's pretty bleeding edge for the general market. I agree with previous posts that the next major PM update will go PCIe, but probably still provide a couple PCIx slots, as well.
  7. macrumors 6502a


    Oct 21, 2003
    I think alienware is moving beyond agp to pci-E, even in their (desktopreplacement/gaming) laptops.

    afaik pciX won't really have gfx cards.

    pci-E on the G5 chipsets would really be nice for upward upgradeability, since I don't see ati/nvidia continuing to make AGPs forever. Hopefully (although less hopefully I admit), this will result in some cost benefit as well for our apple gfx card purchases.
  8. macrumors 604


    Mar 17, 2004
    Melenkurion Skyweir
    Maybe not forever, but for a LONG time to come. They're still making PCI video cards for Chrissakes!
  9. macrumors 6502a

    Sep 19, 2003
    Montréal (Canada)
    I am glad to see that all the marketing hype of the tech industry is working...

    PCIe has NO advantages againts current APG 8x cards. I stated it before but seems like no one ever use the search function of the forum... The reason is simple: current AGP ports arent saturated by the current video cards. There are a lot more room to grow (about 100%) and that is counting the best current cards. So just think about it: you can have a card twice as fast as the x800 with your current PM!

    PCI-e is just hype and a way for the industry to cut cost. I dont know why but it seems like PCI-e cards cost less to make than AGP cards. Also, PCI-e card will allow the creation of lower end card that will use the computer RAM insted of their own, thus reducing the cost.

    All in all, unless there is a big improvement in the video card industry in the next year, AGP 8x will be way enough for still a while, at least a year for serious gamer, 2 - 3 for normal gamer/user. Basicaly, it means that we will see cell computer / video card before there is any real use for it. And by that time, the PCI-e 2.0 standard will be the new norm...

    So I hope you see why I keep saying that PCI-e is of no concern to us.

    * There are a few exception: if you want SLI setup for exemple, but that hardly qualify as a normal type of use, even for serious gamer!
  10. macrumors 6502a


    Mar 13, 2004
    Doesn't really matter right now anyway. Video cards aren't currently even using the full bandwidth of AGP. PCI-E will allow for greater expandability in the future (year or two from now? speculative) but for now I wouldn't worry about it.
  11. nek
    macrumors member

    Aug 26, 2003
    I agree with those who have said there is no need for PCIe yet, and I wouldn't be surprised if Apple went with AGP 8x and PCI-X 2.0 in the next Power Macs.

    PCI-X 2.0 at 533MHz actually has the same theoretical bandwidth as PCIe 16x of 4GB/s, except PCIe can send data in both direction at the same time for a total of 8GB/s and its serial rather than parallel. And PCIe 2.0 will double that when it arrives in 2007.

    But just so that the graphics cards in new Powermacs will be upgradable further into the future, I'd prefer if Apple included PCIe with the next upgrade. Unlike the current situation where new low-end graphics cards are still available for PCI slots, that won't be the case with AGP. ATI still makes the Radeon 9200 PCI card even though Macs have had AGP since 1999 because Macs still have the slots. Once Apple moves to PCIe, I wouldn't expect ATI to make more than one more generation high-end AGP card(s), allowing everyone to upgrade once.
  12. macrumors 6502a


    Aug 26, 2004
    PCI-X 2.0 is a new, higher speed version of the conventional PCI standard, which supported signaling speeds up to 533 megatransfers per second (MTS). Revision 1.0 of the PCI-X specification defined PCI-X 66 and PCI-X 133 devices that transferred data up to 133 MTS, or over 1Gbyte per second for a 64-bit device.

    Revision 2.0 adds two new speed grades: PCI-X 266 and PCI-X 533, offering up to 4.3 gigabytes per second of bandwidth, 32 times faster than the first generation of PCI. Another major feature of the PCI-X 2.0 specification is enhanced system reliability. ECC support has been added both for the header and payload, providing automatic single-bit error recovery and double-bit error detection. These new standards keep pace with upcoming advances in high-bandwidth business-critical applications such as Fibre Channel, RAID, networking, InfiniBand™ Architecture, SCSI, and iSCSI.

    Taken from http://www.pcisig.com/specifications/pcix_20/
  13. macrumors member

    Feb 18, 2005
    It won't take long for graphics card performance to increase 100%. GPU performance is increasing at a rate faster than Moore's Law allows.
  14. macrumors 6502a

    Sep 19, 2003
    Montréal (Canada)
    look at the release date of the first 6800, now look at the current market offering. Almost a year and we are still with the same cards. GPU speed increase arent linear, they are incremental: they go up by big leap each time the manufacturers switch to a new chip technology and each chip last at least a year.

    That is why I said that the APG 8x will be good enough for still a few months, or maybe a year. Personnaly, I think the current offering will last at least until next winter and even then, its only the top card performers that are going to saturate APG8x. So I dont think there is anything to worry about there for at least one more year. But please, Apple, prove me wrong!
  15. macrumors member

    Jun 23, 2003
    Toronto, ON
    Sure, if you look at the change since the 6800 (or the ATI x800) was introduced, things haven't changed much - thats because its still the same architecture and chip. However, look at the performance difference between the 6800 and the previous generations top of the line cards (the fx5950 for nVIDIA and the 9800pro for ATI), and the gap is huge - approaching double, and even higher when you are talking about performance at high resolutions like 1600x1200, especially with 4x AA and 16x Ansio filtering. You cannot deny the last generation of graphics card was a huge leap in performance and technology. Also keep in mind that even the current generation of graphics cards were designed to be AGP cards, then essentially were "ported" to work on the PCIe bus. The next gen of cards will be designed from the outset to take advantage of PCIe fully.

    As for PCIe, I will have to disagree with you somewhat. It is true that the AGP 8x is not near to becoming a bottleneck with current cards, this will obviously not always be the case. I don't see the problem with adopting a technology that will become the future standard. Not only that, but PCIe is designed to replace the aging PCI standard (that must be around a decade old now) which is limited to a bus speed of 33MHz! Surely you agree that PCI is past its prime, and while PCI-X is a good improvement over standard PCI, it has not (nor will it ever) garner the industry support needed to become the replacement for PCI.

    So what's the harm in the next PM revision supporting PCIe? Nothing is future-proof, but the PCI bus is clearly on the way out.

    (edited to add link)
  16. macrumors 6502

    Mar 1, 2004
    The question of whether PCIe is an advantage over AGP is completely irrelevant. The fact is that the next gen GPUs (NV5x and R520) are native PCIe controllers and there is no guarantee that vid card manufacturers will use AGP bridge chips to make AGP versions. Its already startingto happen, the ATI X850XT is not available in AGP.

    Therefore, for Mac users to have any remote chance of keeping up with vid card technology, a PCIe slot is vital.
  17. macrumors 6502a

    Sep 19, 2003
    Montréal (Canada)
    PCIe slot vital?
    I think you totaly miss my point. First, if you look at the current market offering, you will see that there arent many PCIe cards, and most of the ones that are availlable are low-middle end cards. Manufacturers still sell a lot of AGP cards and will continue to do so as long as the buyers only have AGP port.

    In case you didnt know, the video card market is driven by gamers and guess what? Gamers use AMD CPU and board which didnt have PCIe slot until recently. So basicaly the demand for PCIe cards was low until now and will start to increase slowly as gamers are switching board. But why would they change if the current best cards are availlable on AGP? They are probably going to keep their current system until the next major update in the video card market which will probably be in about a year.

    During that time, the PCIe market wont evolve much, only new systems will offer PCIe cards and they arent the bulk of the high end gamers market.

    Basicaly, what this mean is that we still have more than a year before PCIe become standard and by that time we will move to PCIe 2.0. The current PCIe offering is kinda like the AGP2x era which was quickly replaced with AGP4x. Its a theoricaly good improvement but by the time it is used, better standard will emerge.

    Stop thinking about forward combatibility, buy according to your current needs and sell the computer once your needs change!
  18. macrumors member

    Jun 23, 2003
    Toronto, ON
    Actually, I am quite aware of that fact, being a person who builds their own gaming rig and uses only AMD cpu's. In fact, I had been holding off building a new system until AMD boards supported PCIe because (contrary to what you say) the fastest video card available, the ATI x850XT is *ONLY* available for PCIe - just as Bidheadache already mentioned.

    I agree with you the next major update for video cards will probably come in about a year - but wouldn't you rather have a system that will support these new cards, rather than being left out in the cold with an AGP slot?
  19. macrumors 6502

    Mar 1, 2004
    Mantat, you really aren't a forward looking person are you?

    the point I made is that THE best cards are not AGP. I do own an A64 for gaming and I do frequent PC sites like Rage3d, NVNews, and pcforums. PC gamers are hanging out for two things, SLI technology (which is PCIe) and the latest ATi revisions which are biased towards PCIe (that would be the X850XT and X800XL which are PCIe only). The point I am making is that the PC world is starting the transition already (whether you personally like it or not), particularly at the high end. Nforce4 is the hottest AMD chipset available and the majority of enthusiasts have been waiting to upgrade to this chipset. Now that its here, and with the next gen of ATi and NVidia GPUs being PCIe only, that suggests that high end PCIe adoption could reasonably be expected to pickup.

    ANd on the low end, I suggest you read about Nvidia's 6200 Turbocache technology and ATi's X300 hypermemory (both PCIe based). They are both methods for board manufacturers to further reduce the cost of graphics subsystems by reducing the amount of local graphics RAM. Given the cost savings, expect the low end guys to really push this as well.

    The point is, PCIe is here. I am not debating whether it is technically better or not. NVidia and Ati are really pushing it at the high end and low end. PCIe has a number of advantages like SLI (ATI are calling their version something else) which is attracting gamers/enthusiasts (even people only planning on buying 1 vid card want SLI boards). Given this momentum, I would think that its critical for Apple to support PCIe on the vid card front. I mean, its bloody hard enough trying to get vid card manufacturers to manufacture Mac cards now when really all they need is a different BIOS (hence the lack of choice), imagine how hard it will be convincing them to make small MAC AGP production runs of their cards when they are concentrating on PCIe.
  20. macrumors 6502

    Mar 1, 2004
    Man are you behind the times, the ATI range has more PCIe cards than AGP cards now, especially on the high end. And on the NVidia side, the high end is well supported with PCIe versions of 6800Ultra, 6800GT and 6600GT. The only one missing is the vanilla 6800 which remains AGP only.
  21. macrumors 6502a

    Sep 19, 2003
    Montréal (Canada)
    Guys, calm down... I think you arent following my idea, simply thinking that 'the best is better'.

    as I said, I agree that it would be nice if Apple supplied PCIe bus, but they wont for the next revision for the reason I stated above and in other posts.

    Now, sorry but there is nothing I find more ridiculous than an avid gaming who is looking for forward compatibility. we all know that major speed increments are done with technology changes, increments in a technology are minor. For exemple, compare the 9800 vs x800 and x800 vs x850. So, if the big technology changes are done every 1-2 year, you better off building/buying a new system at every technology change insted of changing some parts every 6 months. And these technology changes arent compatible: PCI vs AGP vs PCIe... By the time the PCIe cards are marginaly faster than AGP I think we will be close to cell based video cards which will make everything else obsolete. So yes, I am forward thinking ;-)

    Since the current performance of AGP is about the same as PCIe, there is no need for Apple or us to move ahead to PCIe, YET. I might change my speach this automn or winter, but right now, there is no reason to do so. If you can hold on to buy a new PM until then, go on. But when you are in a production environnement, you dont buy technology, you buy tools that you need right now. I currently have a PM and as soon as PCIe are availlable and with a justified performance boost, I will probably sell my system to get a new one. I am probably not going to lose more than 100$ doing so.
  22. macrumors 6502a

    Jul 22, 2002
    Tacoma, WA
    Regardless of the above graphics card debate (which I don't know a whole heck of about, so I'll just throw in my informed oppinion that PCIe gfx cards are the future compared to AGP), PCIX is simply quite easy to implement in a chip-set compared to PCIe 1.0. Simple as that. Apple didn't put it in because it's a ton of work to add for relatively little value to the targeted users.

  23. macrumors 604


    Mar 17, 2004

    1) Apple put PCI-X on the G5 before PCIe was out and didn't upgrade.
    2) PCIe is owned by Intel, IBM and Apple's competitor.
    3) PCI-X is backwards compatible with PCI cards. PCIe can not use older PCI-X cards.

    Most computers use normal PCI and use PCIe to replace the AGP slot. I think Apple should keep PCI-X for older cards and use PCIe for the graphics, as well.
  24. macrumors 6502a


    Feb 2, 2005
    Its all in the backwards compatibility....
  25. macrumors 6502a


    Aug 26, 2004
    PCIE will go through the same revisions as AGP did, even though we have SLI. Games designers will soon catch up and make use of the features and bandwith that PCIE and with SLI has to offer.

    It will be very interesting if this Cell chip makes its way on to graphics cards, if it lives up all the hipe. Then it should be able to utilise the bus to its fullest.

    PCI-X was designed as a replacement just like PCIE to the original PCI bus, but it was meant for high end machines like servers etc. PCI-X cards like Fibre Channel - Raid (various levels) etc were developed to make use of this interface.

    But just take alook at the 2.0 and 2.5 GHZ Power Mac G5, if you go to Apple store and build a CTO machine then you can add OSX Server - Raid - Fibre Channel and 8 Gig of ram and the likes.

    So in the end you end up with a Mac Server- trying doing that with a PC!

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