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#81
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J. Clarke wrote:
PCI-X is too slow for current graphics cards. It goes up to 133 MHz on 64 bit, but this is only the same speed as AGP 2X. And it would likely have major problems scaling faster in speed because it has such a wide parallel bus. A serial bus like PCI Express is much easier to scale up in terms of speed (look at SATA). (a) PCI-X 2.0 goes to 533 MHz (b) What about SATA? The second revision is not quite as fast as parallel SCSI has been for years, and a lot less flexible besides. As far as PCI-X 2.0, I would guess it's not going to get much or any faster than that, and the cost is huge. From the PCI Express white paper: "Close investigation of the 1990’s PCI signaling technology reveals a multi-drop, parallel bus implementation that is close to its practical limits of performance: it cannot be easily scaled up in frequency or down in voltage; its synchronously clocked data transfer is signal skew limited and the signal routing rules are at the limit for cost-effective FR4 technology. All approaches to pushing these limits to create a higher bandwidth, general-purpose I/O bus result in large cost increases for little performance gain." As far as SATA, the bus doesn't need to be as fast as SCSI since it is a point-to-point bus which is not shared (similar to PCI Express). Also, the performance of current SCSI setups comes at a high cost - SCSI controller hardware seems about an order of magnitude more expensive in many cases.. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from Home Page: http://www.roberthancock.com/ |
#82
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J. Clarke wrote:
Robert Hancock wrote: J. Clarke wrote: I see PCI Express as more of a "stuck with" than a "must have". I think we would all have been better served if they had instead of PCI Express put PCI-X in their chipsets as a standard feature. But that wouldn't have forced one to upgrade any other components in order to replace a motherboard. As I mentioned in another post, PCI-X is not sufficient for use on a video card these days. The fastest version is only the same speed as AGP 2X, we already have AGP interfaces 4 times faster than that.. The fastest version is the same speed as AGP 8x, which, given that no video board currently on the market is bottlenecked at _4_x, would appear to be adequate for video. Your information, from whatever source, is not current. Yes, PCI-X does go up to 533 MHz now, however it's a) extremely expensive and b) not likely to get much faster, whereas PCI Express has a clear upgrade path for the future.. -- Robert Hancock Saskatoon, SK, Canada To email, remove "nospam" from Home Page: http://www.roberthancock.com/ |
#83
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Robert Hancock wrote:
J. Clarke wrote: PCI-X is too slow for current graphics cards. It goes up to 133 MHz on 64 bit, but this is only the same speed as AGP 2X. And it would likely have major problems scaling faster in speed because it has such a wide parallel bus. A serial bus like PCI Express is much easier to scale up in terms of speed (look at SATA). (a) PCI-X 2.0 goes to 533 MHz (b) What about SATA? The second revision is not quite as fast as parallel SCSI has been for years, and a lot less flexible besides. As far as PCI-X 2.0, I would guess it's not going to get much or any faster than that, and the cost is huge. From the PCI Express white paper: "Close investigation of the 1990?s PCI signaling technology reveals a multi-drop, parallel bus implementation that is close to its practical limits of performance: it cannot be easily scaled up in frequency or down in voltage; its synchronously clocked data transfer is signal skew limited and the signal routing rules are at the limit for cost-effective FR4 technology. All approaches to pushing these limits to create a higher bandwidth, general-purpose I/O bus result in large cost increases for little performance gain." Remember when 100 Mb/sec LANS cost $10K/NIC? Time passes, Moore's Law applies, what was impossible in the '90s is cheap in the 21st century. As far as SATA, the bus doesn't need to be as fast as SCSI since it is a point-to-point bus which is not shared (similar to PCI Express). Also, the performance of current SCSI setups comes at a high cost - SCSI controller hardware seems about an order of magnitude more expensive in many cases.. You miss the point entirely. You're claiming that the serial bus has some inherent performance benefit. If that was the case then SATA would be able to outperform SCSI in all regards at lower cost. Instead it only allows one device per cable, runs at a lower speed, and has about a tenth the allowable cable length, which means that it is not a high performance connection in any regard. Further, if there is no need for high performance in SATA then why is there a 3 Gb/sec version of it? As for SCSI controller hardware being "an order of magnitude more expensive", where can one get an SATA2 host adapter at any price? The only ones I can find are built into motherboard chipsets. Regardless, SCSI is targetted at a different market--the price is set by marketing considerations, not by manufacturing cost. Unless you believe that it costs more to make a multiple-die-shrunk 5 year old chip design than it does to make a brand new one. -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
#84
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Robert Hancock wrote:
J. Clarke wrote: Robert Hancock wrote: J. Clarke wrote: I see PCI Express as more of a "stuck with" than a "must have". I think we would all have been better served if they had instead of PCI Express put PCI-X in their chipsets as a standard feature. But that wouldn't have forced one to upgrade any other components in order to replace a motherboard. As I mentioned in another post, PCI-X is not sufficient for use on a video card these days. The fastest version is only the same speed as AGP 2X, we already have AGP interfaces 4 times faster than that.. The fastest version is the same speed as AGP 8x, which, given that no video board currently on the market is bottlenecked at _4_x, would appear to be adequate for video. Your information, from whatever source, is not current. Yes, PCI-X does go up to 533 MHz now, however it's a) extremely expensive So is PCI Express if you're running any kind of hardware that needs more performance than regular PCI delivers. and b) not likely to get much faster, In your opinion. whereas PCI Express has a clear upgrade path for the future.. Clear upgrade for what purpose? What's coming along that needs more than 10 GB/sec? PCI Express exists for one purpose, to put money in Intel's pocket. If you want to buy the hype, go right ahead. But Intel implements all-up PCI-X in _every_ PCI Express chipset they make (read the specs if you don't believe me), so by your reasoning those chipsets, with both PCI-X and PCI Express, should cost more than chipsets that implement PCI-X alone. So much for your argument about cost. -- --John Reply to jclarke at ae tee tee global dot net (was jclarke at eye bee em dot net) |
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