pci latency but no pci slot

[kitoxx88]

Why do alot of current/recent motherboards have a pci latency timer setting but no pci slots?

Just wondering if anyone can shed some light on this as google has nothing definitive. (that i could find).

TIA.

 

[qazzi]

pci latency also applies to the pcie...

 

[TJ Hooker]

pci latency also applies to the pcie...

That doesn't make sense. PCI latency is a measure of how long a single device can assert control of the PCI bus. [strike]PCIe isn't a bus[/strike] PCIe devices don't share a bus, it's point to point, so the concept of asserting/relinquishing control of the bus doesn't apply.

 

[qazzi]

read the defenition of PCIe http://searchdatacenter.techtarget.com/definition/PCI-Express

 

[TJ Hooker]

Ok, sure, here's a quote from the link you posted:

Every device that's connected to a motherboard with a PCIe link has its own dedicated point-to-point connection. This means that devices are not competing for bandwidth because they are not sharing the same bus.

 

[qazzi]

geez... did you read it thoroughly?? at the beginning "Peripheral Component Interconnect Express (PCIe or PCI-E) is a serial expansion bus standard for connecting a computer to one or more peripheral devices."


then the beginning statement of the qoute "PCIe provides lower latency and higher data transfer rates than parallel busses such as PCI and PCI-X. "

it was meant to be a replacement for PCI and PCI-X it is a BUS...

 

[TJ Hooker]

Yes, I did, and I corrected my first post accordingly. However, that doesn't really change the gist of what I was trying to say. Namely, that PCIe is not a shared bus (unlike conventional PCI), and therefore the concept of a PCI latency timer doesn't make sense in the context of PCIe.

 

[qazzi]

EDIT
Ok i retract my 1st answer... it does not apply to PCIe... (but oddly some built in GPU gets boost when you change the PCI timer to 128 even though there supposed to be in PCIe.)

as to answer th OP question:
"The PCI Bus is shared , so only one device on it can transmit data at once. The PCI Latency Timer controls how long each device has control over the bus before another can be switched to. Remember, sound cards, IDE/SATA controllers, NIC and other devices are all on the PCI bus, some need to send data to the CPU, some directly to ram. When they have control over the PCI bus, their data goes to the PCI controller on the SB, then through some sort of link to the NB (V-link on Via chipsets, HyperTransport on Nvidia Chipsets) where it goes into memory (if it's a dma transfer), or directly on to the CPU. The latency timer keeps one device from tying up all of the PCI bus, when there are other devices that need to use it also. '
(also some mobo has a PCI to PCIe Bridge it is also affected by the timer, i do know this is maybe why some people have a poor PC performance.)

 

[harrystam]

Side note: You can put a PCI E 1 card in a PCI E x16 slot and it will work just fine.