PCIe lanes
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I am happy with my 2014 vintage PC; I have no need to replace it. I just recently installed another 32 TB of magnetic disk, and will get a 1 TB M.2 system disk next week - that will keep the PC going for a few more years :-) Before ordering the M.2 disk, I checked the motherboard user guide to make sure it would accept it. The guide listed the PCIe capacities with "40 lane" and "28 lane" CPUs. Mine, an i7 5820K, has "only" 28 PCIe lanes. So I checked up the Core CPUs of today, to see which models would provide more, starting at the top of the list from Intel, sorted by release date. I gave up before I found any model with more than 20 (which they all had). I also noticed that while my old CPU has four memory channels, most new ones only have two. I am certainly no hardware expert, but to me, this looks like a downgrade, on both points. In spite of significant faster memory chips today, the max memory bandwidth is only marginally higher (less than 15%) on today's CPUs. I am curious about why this is so. Did Intel conclude that PCIe wasn't such a great success after all - there is no need for that many lanes? With my Asus X99-A/USB3.1 board, I can plug in and bridge together three GPU cards. Nowadays, it seems as if most users want a single super-powerful card. Is that why we don't need that much PCIe any more? In 2014, I expected super-speed network interface boards to be PCIe based. I expected super-speed storage to be PCIe based, but all I see is a single M.2 socket. Does it tell that PCIe was (at least partially) a flop, replaced by USB4 for network, disks and other uses? For the memory bandwidth: Did Intel conclude that memory bandwidth isn't any serious bottleneck at all? Maybe I am right in concluding that my 2014 vintage PC is good enough for a few more years ...
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I am happy with my 2014 vintage PC; I have no need to replace it. I just recently installed another 32 TB of magnetic disk, and will get a 1 TB M.2 system disk next week - that will keep the PC going for a few more years :-) Before ordering the M.2 disk, I checked the motherboard user guide to make sure it would accept it. The guide listed the PCIe capacities with "40 lane" and "28 lane" CPUs. Mine, an i7 5820K, has "only" 28 PCIe lanes. So I checked up the Core CPUs of today, to see which models would provide more, starting at the top of the list from Intel, sorted by release date. I gave up before I found any model with more than 20 (which they all had). I also noticed that while my old CPU has four memory channels, most new ones only have two. I am certainly no hardware expert, but to me, this looks like a downgrade, on both points. In spite of significant faster memory chips today, the max memory bandwidth is only marginally higher (less than 15%) on today's CPUs. I am curious about why this is so. Did Intel conclude that PCIe wasn't such a great success after all - there is no need for that many lanes? With my Asus X99-A/USB3.1 board, I can plug in and bridge together three GPU cards. Nowadays, it seems as if most users want a single super-powerful card. Is that why we don't need that much PCIe any more? In 2014, I expected super-speed network interface boards to be PCIe based. I expected super-speed storage to be PCIe based, but all I see is a single M.2 socket. Does it tell that PCIe was (at least partially) a flop, replaced by USB4 for network, disks and other uses? For the memory bandwidth: Did Intel conclude that memory bandwidth isn't any serious bottleneck at all? Maybe I am right in concluding that my 2014 vintage PC is good enough for a few more years ...
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Commonly 4 PCIe lanes are used for the M.2 socket, or SATA but using that for the main SSD is a bit behind the times
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So 4 lanes for your M.2 system disk, 16 lanes for your GPU. That is it, as I understand it. Forget PCIe for anything else. Or did I miss something?
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I am happy with my 2014 vintage PC; I have no need to replace it. I just recently installed another 32 TB of magnetic disk, and will get a 1 TB M.2 system disk next week - that will keep the PC going for a few more years :-) Before ordering the M.2 disk, I checked the motherboard user guide to make sure it would accept it. The guide listed the PCIe capacities with "40 lane" and "28 lane" CPUs. Mine, an i7 5820K, has "only" 28 PCIe lanes. So I checked up the Core CPUs of today, to see which models would provide more, starting at the top of the list from Intel, sorted by release date. I gave up before I found any model with more than 20 (which they all had). I also noticed that while my old CPU has four memory channels, most new ones only have two. I am certainly no hardware expert, but to me, this looks like a downgrade, on both points. In spite of significant faster memory chips today, the max memory bandwidth is only marginally higher (less than 15%) on today's CPUs. I am curious about why this is so. Did Intel conclude that PCIe wasn't such a great success after all - there is no need for that many lanes? With my Asus X99-A/USB3.1 board, I can plug in and bridge together three GPU cards. Nowadays, it seems as if most users want a single super-powerful card. Is that why we don't need that much PCIe any more? In 2014, I expected super-speed network interface boards to be PCIe based. I expected super-speed storage to be PCIe based, but all I see is a single M.2 socket. Does it tell that PCIe was (at least partially) a flop, replaced by USB4 for network, disks and other uses? For the memory bandwidth: Did Intel conclude that memory bandwidth isn't any serious bottleneck at all? Maybe I am right in concluding that my 2014 vintage PC is good enough for a few more years ...
There are PCIe lanes that originate from the cpu and others from the chipset. The cpu really only needs 20. The chipset can have up to 24 more. The speed of the PCIe bus has about doubled with each new version. PCIe 2.0 was 500MBs on each lane. PCIE 3.0 was just under 1000. PCIe 4.0 is just under 2000. A PCIe 3.0x4 M.2 can hit over 3000MBs. A PCIe 4.0 can do twice that. It leaves anything else in the dust, even an SSD on SATA 6Gbs (note the lower case “b” on the SATA spec). Most GPU processing is done on the card and sent straight to the monitor(s). All but the very expensive top end ones really only need 8 PCIe 3.0 or 4.0 lanes. Here’s an article that explains it pretty well: Guide to PCIe Lanes: How many do you need for your workload?[^] I’m not up to date on memory throughput but I would be surprised if the story there was any different. I would expect an i5-11xxx cpu with a Z590 chipset and a PCIe 4.0x4 m.2 SSD would benchmark three to five times faster than an i7-5xxx with x99 and PCIe 3.0x4 m.2.
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I am happy with my 2014 vintage PC; I have no need to replace it. I just recently installed another 32 TB of magnetic disk, and will get a 1 TB M.2 system disk next week - that will keep the PC going for a few more years :-) Before ordering the M.2 disk, I checked the motherboard user guide to make sure it would accept it. The guide listed the PCIe capacities with "40 lane" and "28 lane" CPUs. Mine, an i7 5820K, has "only" 28 PCIe lanes. So I checked up the Core CPUs of today, to see which models would provide more, starting at the top of the list from Intel, sorted by release date. I gave up before I found any model with more than 20 (which they all had). I also noticed that while my old CPU has four memory channels, most new ones only have two. I am certainly no hardware expert, but to me, this looks like a downgrade, on both points. In spite of significant faster memory chips today, the max memory bandwidth is only marginally higher (less than 15%) on today's CPUs. I am curious about why this is so. Did Intel conclude that PCIe wasn't such a great success after all - there is no need for that many lanes? With my Asus X99-A/USB3.1 board, I can plug in and bridge together three GPU cards. Nowadays, it seems as if most users want a single super-powerful card. Is that why we don't need that much PCIe any more? In 2014, I expected super-speed network interface boards to be PCIe based. I expected super-speed storage to be PCIe based, but all I see is a single M.2 socket. Does it tell that PCIe was (at least partially) a flop, replaced by USB4 for network, disks and other uses? For the memory bandwidth: Did Intel conclude that memory bandwidth isn't any serious bottleneck at all? Maybe I am right in concluding that my 2014 vintage PC is good enough for a few more years ...
A 28/40 lane CPU means you have an HEDT (high end desktop) chip, aka a "Xeon we stripped a few features out to make in unattractive to businesses so we can soak them for an extra gigabuck" or an actual Xeon. 16 lanes from the CPU has long been the baseline for mass market consumer chips; enough for a GPU (or 2 if bifurcated) along with an additional 10-20 multiplexed over an x4 sized link on the chipset. More recent designs are starting to edge this up, with 20 on Intel boards giving an x4 direct to the CPU for the primary (and in 99% of cases only) SSD; they're also upgrading the chipet link to an x8 meaning a single SSD can't saturate it and making the dedicated CPU lanes as much me-too marketing as anything else. Consumer tier AMD chips will claim 24/28 CPU lanes; but since 4 of those are used to connect the chipset (vs intel using DMI (pronounced "not-PCIe" lanes, and created to kill off 3rd party chipsets ~15 years ago) the effective number for comparison with intel is 20/24 and AFAIK they're sticking with just x4 to the chipset. It's the same thing with memory channels. 2 has been the consumer baseline for about 20 years, with high end ones offering higher counts. In both cases this is avoiding overkill on consumer systems while keeping costs down - adding extra layers to the PCB, especially at the quality levels needed for modern high speed signalling - is really expensive. The bigger socket doesn't help either. Nor does the fact that the big OEMs prefer smaller than ATX mobos which really makes fitting more than 4 dimm sockets problematic.
Did you ever see history portrayed as an old man with a wise brow and pulseless heart, weighing all things in the balance of reason? Is not rather the genius of history like an eternal, imploring maiden, full of fire, with a burning heart and flaming soul, humanly warm and humanly beautiful? --Zachris Topelius