Performance and PCI Express Bus Lanes
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Date: Fri, 01/16/2015 - 10:22
The amount of PCI Express lanes you have available to you through your PC, largely depends on your CPU and your chipset. With Intel’s more modern chipsets, your CPU largely determines how many PCI lanes you have available to you through your PC. As of the time of this writing, all Socket 1150/1151 CPUs support 16 lanes of PCI-Express bus lanes, and all Socket 2011v3 CPUs support 40 lanes of PCI-Express bus lanes, except the lowest end i7 CPUs (which has 28 lanes).
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Why Do PCI-Express Lanes Matter?
Your PCI Express lanes consist of the lanes of communication that your motherboard uses to control your PC's functions. Your CPU, in particular controls your CPU, memory, and those functions that have to do with your PCIe slots.
- Video card
- Onboard Video
- Sound card
- Network card
- RAID controller card
- PCIe hard drives
- Specialized PCIE cards
Other functions use your chipset PCIe bus lanes. Older chipsets typically designate 6-8x PCIe 2.0 lanes for these functions. Z170 and H170 boards (higher end Skylake boards) designate 20 and 16 PCIe 3.0 lanes. Functions which your chipset's PCIe lanes control may include:
- SATA hard drives
- Onboard Sound
- Onboard RAID
- Onboard Network Controller
- PCIe cards plugged into your PCIe x1 slot
- All PCIe slots except the first one (Socket 1150/1151)
The following are generally accepted amounts of PCIe bandwidth which various components require:
- 8-16 Lanes - x16 PCIe Video Cards (Each)
- 8-16 Lanes - FPGA & Other Specialized PCIe Cards
- 4-8 Lanes - SSD Drives
- 4 Lanes - Thunderbolt (TB uses 2 lanes PCIe 2.0, TB 2 uses 4 lanes PCIe 2.0, and TB 3 uses 4 lanes PCIe 3.0)
- 4 Lanes - Hardware Based RAID Controllers
- 1 Lane - Sound
- 1 Lane - Network Controllers
Performance PC Demands
The number of PCIe bus lanes you have available to you can determine the performance of your PC, particularly if you are using performance sensitive software, such as Photo/Video Software, CAD, Financial Software, Audio Production Software, etc. Also, if you use your PC for intensive gaming application or to support multiple high-definition monitors, you will have an increased demand placed on your PCIe bus lanes.
If you aren’t using your PC for performance demanding applications, it isn’t likely you need more than 16 lanes of PCIe bus.
However, if you are planning to use your system for applications that may add up to more than 16 lanes of bus bandwidth, then using Socket 1150/1151 (16 lanes of bandwidth), may become a bottleneck for your system during times of intense usage.
Side Note: another interesting caveat is that your PC uses DMI to communicate between your CPU's PCIe bus lanes and your Chipset's PCIe bus lanes. X99 (Socket 2011v3 i7 CPUs), Z97 (Socket 1150), and H97 (Socket 1150) all use DMI 2.0, which is the equivalent of four PCIe 2.0 bus lanes (about 2 GB/s or 17.2 Gb/s). Z170 and H170 Skylake boards now use DMI 3.0, which is the equivalent of four PCIe 3.0 bus lanes (about 3.93 GB/s or 33.8 Gb/s). If you have several chip-side devices communicating to your CPU side bus, this may be your bottleneck in your PC. Z170 and H170 Skylake boards are much less likely to have this issue because the speed of their DMI effectively just doubled. On the other hand, if you are considering Socket 2011v3, the overall bus for your CPU is greater than it would be for Socket 1151 (Skylake-S) and if you are using PCIe card based products, those are mostly on the CPU side on those PCs and they won't need DMI to communicate with the CPU.
PCIe 3.0 Effective Speed
When all PCIe bus lanes are being used on a PC, your PC negotiates which device gets how much PCIe bandwidth. Most of the motherboards we use in our systems use the latest version of PCIe. This version of PCIe is referred to as PCIe 3.0. PCIe 3.0 has almost doubled the effective bandwidth (after overhead) of each PCIe bus lane when compared to PCIe 2.0. PCIe 2 had 500 MB/s effective bandwidth. PCIe 3.0 has 985 MB/s effective bandwidth.
If you are using PCI 3.0, even though your PC negotiates less PCI lanes during peak usage, under normal circumstances your overall performance isn’t likely to suffer. This is because the overall bandwidth of each PCIe bus lane has just doubled. However, if you are using your PC for demanding applications, it is recommended that you choose a system with more available PCIe lanes (Socket 2011v3).
Socket 1150, Socket 1151, or Socket 2011v3?
Socket 2011v3 is Intel’s performance line of CPUs. Overall, these CPUs have more performance potential than Socket 1150 CPUs. However, they have their drawbacks. Socket 2011v3 CPUs are more expensive (and the motherboards supporting them are more expensive) and they produce more heat (and use more power).
The following chart explains the performance, bus lanes, and power usage of various socket designs (featured in our quiet PCs), to help you make your decision about which PC is right for you. In our chart, we used Passmark CPUMark rankings from this resource (as of the time of this writing), for your convenience. If you wish to look up your particular CPU's performance please refer to: https://www.cpubenchmark.net/cpu_list.php
|SOCKET TYPE||CPU Mark
|PCI Bus Lanes||CPU Watts|
|Socket 1151 Thin Mini ITX (Low Wattage)||4778-5274||16 PCIe 3.0 (H110 chipset has 6 lanes PCIe 2.0)||35w|
|Socket 1150 Celeron to i7||2995-11192||16 PCIe 3.0 (H97 chipset has 8 PCIe 2.0 lanest)||53-88w|
|Socket 1151 (Skylake) - Pentium to i7
||4013-10999||16 PCIe 3.0 (Z170 chipset 20 PCIe 3.0, H170 chipset 16 PCIe 3.0)||51-91w|
|Socket 1151 (Skylake) - E3 v5 DDR4 ECC
||7253-10233||16 PCIe 3.0 (C232 chipset 8x PCIe 3.0)||80w|
|Socket 2011v3 i7 DDR4||12949-16023||28-40 PCIe 3.0 (X99 chipset 8x PCIe 2.0)||140w|
|Socket 2011v3 DDR4 ECC E5 v3||4986-22740||40 PCIe 3.0 (C612 chipset 8x PCIe 2.0)||85-145w|
|Dual Socket 2011v3 DDR4 ECC E5 v3||8305-30217||80 PCIe 3.0 (C612 chipset 8x PCIe 2.0)||170-290w|