PCIe, How does the Bios Know?

Discussion in 'BIOS Mods' started by catgirl, Apr 28, 2016.

  1. catgirl

    catgirl MDL Novice

    Jan 15, 2014
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    #1 catgirl, Apr 28, 2016
    Last edited: Apr 29, 2016
    Hey guys,

    Wondering if there is a guru here that knows the following:

    How does the bios know if a PCIe card is in a slot?
     
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  2. EFA11

    EFA11 Avatar Guru

    Oct 7, 2010
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    when the slot is empty there isn't a complete circuit, when a card is in the slot the circuit is made complete and lights flash, go-go dancers kick and the bios goes. OH there is a card in that thurr slot :D
     
  3. Michaela Joy

    Michaela Joy MDL Crazy Lady

    Jul 26, 2012
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    Take a look here. https://en.wikipedia.org/wiki/Conventional_PCI

    Hopefully, this will help you. :)
     
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  4. Myrrh

    Myrrh MDL Expert

    Nov 26, 2008
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    While Michela Joy's answer is probably the most accurate, EFA11's is more fun to read and gets the basic concept right.
     
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  5. Michaela Joy

    Michaela Joy MDL Crazy Lady

    Jul 26, 2012
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    @Myrrh: So true :D
     
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  6. catgirl

    catgirl MDL Novice

    Jan 15, 2014
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    Well I was hoping for a most serious reply.
    And thank you Michaela for your reply, but that shows up on the first page of searches and really still does nothing to answer the original question:
     
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  7. MrMagic

    MrMagic MDL Guru

    Feb 13, 2012
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    Because that is the job of the BIOS, to detect hardware
     
  8. Joe C

    Joe C MDL Guru

    Jan 12, 2012
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    Did you read the Wiki that Michaela posted?
    The answer was there plus much more informative info. Nice post Michaela!
     
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  9. Michaela Joy

    Michaela Joy MDL Crazy Lady

    Jul 26, 2012
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    @catgirl: EFA's answer popped in about 2 seconds before I posted my reply. :)

    I admit that the reading is a bit dry, but that Wiki pretty much describes what's going on.

    And MrMagic is right; The BIOS interrogates each piece of hardware on the local bus and determines how to set it up, based on the card reply. How the hardware responds should be in that Wiki. At the very least, you should be able to find a thread describing the response of the hardware to the BIOS. But you don't need that info, unless you're troubleshooting a PCI card at the chip level. Then, you'd stick a logic analyzer on the local bus and watch for the burst.
    (Been there...done that :D )

    Just curious. Are you learning hardware design?
     
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  10. EFA11

    EFA11 Avatar Guru

    Oct 7, 2010
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    I was serious.

    When the PCIe is placed in the slot it makes the connection and the bios knows it is inserted. Very simple. The same thing when you place a light bulb to a battery.

    [​IMG]

    The PCIe is the exact same thing as this bulb. When its inserted the circuit is complete. The difference is, the bios detects the circuit is complete and is programed to say so. In the case of the light bulb, it is the PCIe and the Bios in one, the light coming on is the indicator that the circuit is made.
     
  11. MrMagic

    MrMagic MDL Guru

    Feb 13, 2012
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    BIOS is also programmed to read the hardware ID and list exactly what make/model hardware you have inserted, it's specs / default clocks / voltage / timings, and set them accordingly

    As long as the BIOS has been updated to support said hardware
     
  12. JFKI

    JFKI MDL Expert

    Oct 25, 2015
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    Please bear with me.

    The following is taken from http://pinouts.ru/Slots/PCI_pinout.shtml and describes the PCI-X scheme.

    PCI-e is an evolution of PCI-X and uses basically the same scheme.
    If you wish to delve into more detail, I suggest you read and understand the PCI-e specification.
    Start here: https://www.slac.stanford.edu/grp/l...ds/CB-PCI_Express_Base_r3.1_October8-2014.pdf
     
  13. LatinMcG

    LatinMcG Bios Borker

    Feb 27, 2011
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    #13 LatinMcG, Apr 30, 2016
    Last edited: May 1, 2016
    unless :biggrin: its an old G31m pci-e v1 and the amd R9 is pci-e v2 and shows all subsystem ids 0000 on post screen :eek: (intel i7 coming soon)
     
  14. bludgard

    bludgard MDL Member

    Jan 4, 2011
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    Been changing out PCIe cards for days looking for this phenom... any special card I need to look for?
    :D
     
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  15. bpwnes

    bpwnes MDL Member

    Aug 11, 2015
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    I have an old X1600 Pro that has a picture of a lady on it... Maybe you need to try one of those?
     
  16. bludgard

    bludgard MDL Member

    Jan 4, 2011
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    Lookin at this one on eBay... cute and reminds me of Ada Wong.
    Only issue is that it is AGP: Doesn't matter; I will try anything to see the go-gos a kickin'. :tasty:
    [​IMG]
     
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