OCing PCI-E 1.0/1.1 to 200MHZ for GPU compat with PCI-E 2.1 - safe?

Ok, so I've got a cheap/old motherboard* which only has 1x PCI-E 1.0 or 1.1 port, probably 1.0.
I've got a Radeon HD 6850 which is a PCI-E 2.1 card, but is backwards-compatible with PCI 1.0 or 1.1 ports (not sure if with both or just v1.1, but either way the card is working on my computer).

However, I noticed that I have a setting in my Bios to change the (only 1x) PCI-E port from the default and minimum 100MHZ to a maximum of 200MHZ [and every 1 point in between], which is, as far as what I read, the regular speed of a PCI-E 2.1 port.

And I was wondering if I should try testing this option (OCing PCI-E to 200MHZ) out to test for increased performance - that is performance closer to what it's designed for on a PCI-E 2.1 port.
However is this at all risky for some reason? I mean can the PCI-E 1.0/1.1 port handle it? And it's only set to 100 MHZ by default because PCI-E 1.0/1.1 gear aren't generally designed for any higher speeds? (or is there something else to it which I should be aware:heink:)


*For the record the MB is a G31TM-P21.

Also, I wasn't sure what category to put this in; MB-OC or GPU-OC, but yeah.
4 answers Last reply
More about ocing 200mhz compat safe
  1. No it cannot handle it, the electrical and logical specifications are different.

    Do not change your PCIe bus speed. You will damage something
  2. +1 dont do it.

    if it was safe there would have been a bios update for the board and you would have had an easy option (AUTO) to switch between 1.x and 2.x

    Quote:
    The industry-standard reference clock frequency used for devices supporting PCIe 1.1, 2.1 and 3.0 is 100 MHz (±300 ppm generated using an HCSL signal format). It is common for embedded processors, system controllers and SoC-based designs to use 100 MHz HCSL format as the reference clock for the PCIe bus interface circuitry.


    from this PDF below (1/2 way down page 3)
    http://www.silabs.com/Support%20Documents/TechnicalDocs/PCIe-Clock-Source-Selection.pdf
  3. Oh yeah, you guys are right about the bus-speed of all PCI-E (being 100MHZ only), I don't know where I got the idea of PCI 2.x having a higher bus-speed from.

    Thanks.
  4. Viqing said:
    Oh yeah, you guys are right about the bus-speed of all PCI-E (being 100MHZ only), I don't know where I got the idea of PCI 2.x having a higher bus-speed from.

    Thanks.


    100Mhz is the reference clock speed that is pumped into the controller logic. The controllers themselves have a PLL which control the IO rate. PCIe 1.x has a transfer rate of 2.5 GT/s (Giga transfers per second) and uses 8b/10b encoding. The encoding results in only 80% of the transmitted data being actual payload data, the rest is used to reduce errors and improve signal tracking. This results in 2.0 GT/s of actual payload data which comes out to 250 megabytes per second per lane. PCIe 2.0 increases this to 5.0GT/s with the same encoding scheme, resulting in 500 megabytes per second per lane. PCIe 3.0 increases this to 8.0GT/s but changes the encoding scheme from 8b/10b to 128b/130b, decreasing the transmission overhead from 20% to 1.5%. This results in just under a gigabyte per second per lane
Ask a new question

Read More

Motherboards PCI Express Overclocking