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A bunch of Noob PCI questions

post #1 of 3
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Please do not cite the Wikipedia PCI-e article for your answer or I will beat you senseless with a virtual noodle. Thanks in advance!

1. PCI-e comes in x1, x4, x8, and x16. Yet sometimes people say "Don't put your x16 GPU in an x8 slot. Is this not hardware/physically impossible unless the slot is open-ended?

2. Motherboards I've seen have open-ended PCI-e x1 slots. That is, you can actually fit the end of the connectors into this slot using a PCIx16 card.... What is the impact on performance to have an x16 card hanging most of the way out of an x1 slot? What about an x16 card in an open ended x8 slot?

3. Why do manufacturers make PCIx16 slots that are "electrically" an x8 slot? What does that mean? (may relate to question 1) Why not make PCIx16 a PCIx16 through and through?

4. What's the story on PCI-e 3.0 and is it even necessary or is 2.0 still working alright?
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Heisenberg
(10 items)
 
Redemption
(18 items)
 
 
CPUGraphicsRAMHard Drive
Intel Core 2 Extreme @ 2.8GHz (upgrade) Intel GMA 950 2 x 2 DDR2 667MHz (upgrade) 120GB Mushkin ECO2 
Optical DriveOSMonitorPower
Replaced with 42 W/hr aux battery Mint 17.3 1280x800 Dell 65w Dell Adapter 
CaseOther
Latitude D630 Chassis Intel 7260-802.11ac 2x2 
CPUMotherboardGraphicsRAM
Not telling AsRock something Pixel Pusher 2 x 8 GB AMD Radeon RAM @ 1600mhz (All the VM's) 
Hard DriveHard DriveHard DriveOptical Drive
Crucial M4 128GB (8 second boot) Western Digital RE4 1TB Western Digital RE4 2TB Pioneer Blu-Ray Reader/Writer 
CoolingOSMonitorKeyboard
Cooler Master Hyper 212 Evo Windows 8.1 Pro x64 Dell U2713HM IBM Model M (CLICKY!!) 
PowerCaseMouseAudio
Antec HCG-900 NZXT Source 210 (it was cheap) Logitech G502 Schiit Modi 
AudioAudio
Sennheiser HD 598 M-Audio AV40's 
CPUMotherboardGraphicsRAM
Intel Core i5-4200U Microsoft BGA1168 Intel HD 4400 8 GB LPDDR3 Dual Channel @ 1600mhz 
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post #2 of 3
I wasn't aware that they made different sized slots for x8 and x16, unless they did a long time ago when pci E first started..

With that said..

1. I'm not sure who would refer to a GPU as "x8" or "x16" since that is the slot type, not the GPU. the x1/8/16 refers to bandwidth that the slot supports.

2. I don't think a GPU or full PCI E card of any sort would even run in a x1 slot, only cards made for x1 will work. Not entirely sure, but even if a GPU or some other card worked in an open ended x1 it would probably be severely gimped.

3. The reason for some slots being the lesser speed is because the southbridge/northbridge (not sure which of those 2) are curently limited to so many pci E lanes per chip. 32 I think may be about the standard limit right now. This lets manufacturers put several pci E slots into a board at varying speeds, such as 4 slots running at x8 x8 x8 x8, or 2 slots running at x16 + x16 full speed. So in short, its a hardware limitation.

4. PCI E 3.0 is just the latest revision to the spec. version 2.0 is still very fast and modern GPU's really can't even take advantage of it fully except in rare cases, if at all. 3.0 is actually unnecessary at present, but advancing tech is always good so bring it on.
post #3 of 3
So basically you want a non-technical answer? Ok here goes...


Quote:
1. PCI-e comes in x1, x4, x8, and x16. Yet sometimes people say "Don't put your x16 GPU in an x8 slot. Is this not hardware/physically impossible unless the slot is open-ended?
Performance is not guaranteed to be the maximum unless its in a 16 lane slot, although it will work in an x8 or x4.

Quote:
2. Motherboards I've seen have open-ended PCI-e x1 slots. That is, you can actually fit the end of the connectors into this slot using a PCIx16 card.... What is the impact on performance to have an x16 card hanging most of the way out of an x1 slot? What about an x16 card in an open ended x8 slot?
A GPU will run in an open ended x1 slot but it will not have any performance at all. Basically windows will recognize the hardware and thats about all the further it will go. 1 lane is necessary to "run" the hardware. The others are to communicate data to it more quickly which is a must for a GPU (throughput). Think of it in terms of networking, its like 10/100/1000 ethernet. Same plug but varying speeds for different uses. A sound card doesn't need 16 lanes of throughput, but a video card definitely does.

Quote:
3. Why do manufacturers make PCIx16 slots that are "electrically" an x8 slot? What does that mean? (may relate to question 1) Why not make PCIx16 a PCIx16 through and through?
It means it only has pins that allow an x8 connection. This is different than an x16 pinned slot that can run at x4 or x8 speeds depending on the chipset and how many things are plugged in and assigned lanes, for example the X58 has more total lanes available than the p67 chipset so it can run 3x 16 slots without resorting to a switching chip like NF200.

Quote:
4. What's the story on PCI-e 3.0 and is it even necessary or is 2.0 still working alright?
3.0 has a higher voltage on the PCI-E bus and would allow for higher end GPU's with less power connections, it also supposedly doubles the bandwidth.

You really might as well read that wiki page
Edited by Scorpion49 - 10/2/11 at 8:28pm
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