How does all the x16/x8/x16/x8 etc work in regards motherboard slots, graphics cards and PCI lanes

[spikeysonic]

Can Someone explain how these PCI slots work and what is meant by stuff like this in regards mother board PCI slots and graphic cards (other than the physical slots I can see) vs PCI lanes

ie how does this work?


Expansion Slots
4 x PCIe 3.0 x16 (supports x16/x8/x16/x8*), 1 x PCIe 2.0 x4, 1 x PCIe 2.0 x1

vs

7 x PCIe 3.0/2.0 x16 (single x16 or dual x16/x16 or triple x16/x16/x16 or quad x16/x16/x16/x16 or seven x16/x8/x8/x8/x8/x8/x8)

 

[Barty1884]

Trying to "in a nutshell" this answer.

There are CPU PCIe lanes + chipset PCIe lanes. Storage, USB etc will all use some of the available lanes.
For example, an i9-9900K has a maximum 16 PCIe lanes.
https://ark.intel.com/products/186605/Intel-Core-i9-9900K-Processor-16M-Cache-up-to-5-00-GHz-

The chipset, Z390 adds 24 PCIe lanes.
https://ark.intel.com/products/133293/Intel-Z390-Chipset

For a total of 40. So, even before you factor in storage, USB etc, you can see there's no way a Z390 board could offer 3x x16 slots (=48 lanes), as it's just not available. Add an M.2 x4 slot or two (= x8 lanes used), there's only 32 left. In theory, you could still have dual x16 slots.... but some of those lanes are needed elsewhere. Meaning the max you will see is a single x16, or dual x8 bandwidth.


Vs an HEDT chip, like an i9-9980XE has 44 PCIe lanes:
https://ark.intel.com/products/189126/Intel-Core-i9-9980XE-Extreme-Edition-Processor-24-75M-Cache-up-to-4-50-GHz-

And the corresponding chipset bring another 24.

So, with that chip, you could theoretically have 3x full x16 slots, assuming the remaining 16 lanes are sufficient for elsewhere.


Those '*' will direct to further info on a spec page, which typically link to the CPU installed.
I don't know what boards you're comparing here specifically.

in the examples.
1.
4 PCIe slots, physically & electrically wired to be x16. With one slot populated, you can have x16 bandwidth (if required, for a GPU, for example).
If you populate the second corresponding slot, then both with run at x8 bandwidth/speeds (for SLI/Crossfire, etc).

2.
Based on the spec listed, this example could support 4x full x16 slots, and have provide maximum bandwidth to each (x16), or one slot at the full x16, and 6 others at x8.
Working that back though, you'd need 4 x16, or 1x 16 + (6x8) = 64 lanes..... and that's before anything else, likely storage.

As for CPU lanes vs Chipset, refer:
https://www.youtube.com/watch?v=JVihgHoy8Sg

 

[spikeysonic]

Its part of the go with 19- 7900x i9-9900x or amd 2050 / or 1950x argument.

with the I9s there is the possibility of a asus sage mother board... this had 7 pci physical slots, but for some dumb reason lacks mid board usb 2 for fittign a liqiuid cooler according to PCSpecialist

ASUS® WS X299 SAGE

https://www.asus.com/us/Motherboards/WS-X299-SAGE/

Intel LGA 2066 CEB motherboard with quad-strength graphics supports, DDR4 4133MHz, dual M.2 & U.2, USB 3.1 Gen 2 connectors, and ASUS Control Centre

• 4-Way PCI-E Gen3 x16 link supporting NVidia GeForce SLI® and AMD CrossFireX™ on demand.

• Ultra-efficient VRM heatsink: Metal fin array connected to large surface area via a heatpipe tames X299 thermals to enable unthrottled performance.

• 5-Way Optimisation: One-click, system-wide tuning, delivers optimised overclocking and intelligent cooling for a diverse range of workloads.

• Industry-leading cooling options: Comprehensive controls for fans and water pumps, via Fan Xpert 4 software or the acclaimed ASUS UEFI

• ASUS Control Centre: A software utility that provides convenient, secure and cost-saving centralized IT management for small and medium businesses.

• Next-gen transfer speeds: Up to 32Gbps dual M.2 and U.2, plus up to 10Gbps USB 3.1 Gen 2 Type-A and Type-C front connector
Detailed Specification
RAM Slots
8 x DIMM, max. 128GB, DDR4 2666MHz
Expansion Slots
7 x PCIe 3.0/2.0 x16 (single x16 or dual x16/x16 or triple x16/x16/x16 or quad x16/x16/x16/x16 or seven x16/x8/x8/x8/x8/x8/x8)
SATA Ports
8 x SATA 6Gb/s ports, 2 x M.2 Socket 3
USB Ports
1 x USB 3.1 Type-C port, 10 x USB 3.1 ports (7 at back panel, 3 mid-board), 4 x USB 2.0 ports (4 at back panel)
Networking
1 x Intel® I210-AT Gigabit LAN, 1 x Intel® I219-LM
Audio
Realtek® ALC S1220A 7.1-Channel High Definition Audio

with the AMD there seems to be a poorer choice


... there wont be a room but open up the choice of motherboards here

https://www.pcspecialist.co.uk/computers/amd-x399-pc/