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PCI x16 Video Cards and x(1/4/8/16) slots

By Savage1701
Jul 24, 2007
  1. OK, if anyone can help me with this I would appreciate it. I understand that PCI express video cards have a physical x16 connector they plug into on the mobo, but what about the electrical specs of that connector? I have an Asus MB that runs some of the 4 x16 physical video cards at electrical x8, and some at electrical x4, and one at electrical x16; all the slots are physical x16. Yet I can run a video card just fine in each of them.

    My question is this: What is the minimum electrical specification (x1, x4, x8) that a physical x16 video card can run under? If I have a physical x16 slot that runs at electrical x1, will my video card function in it? Or is it more complex? Do slots "borrow" electrical x-capacity or "lanes" from each other? Are there a certain number of electrical lanes that can be dynamically allocated amongst available slots?

    I understand a card would no doubt take a performance hit, but since all my work is 2D financial stuff that is irrelevant. I don't need fast frame rates, etc. I'm just lookin' to up my monitor count.

    Thanks for any help with this.
  2. raybay

    raybay TS Evangelist Posts: 7,241   +10

    The electrical part is built into the slot... they are all the same electrically. But operational software differences are built into the motherboard and processed by the chipset in communication with the card that is installed.
    If the card is a 4x card, it cannot work faster in a 16x board, but that board can usually run any card slower at the design speed of the card. A board that has only 1x specifications, cannot run any card that is faster, but a boad that has 16x specifications can usually run a card that older specifications.
    All specifications come to play... the card, the motherboard, the chipset, the drivers of the card. But these are not "electrical" but rather processes.
  3. Savage1701

    Savage1701 TS Enthusiast Topic Starter Posts: 153

    That's about what I figured you would reply, so how can these physical x16/electrical x4 slots run these graphics cards? I am specifically referring to a quad x16 board that Asus makes, the WS64 Pro, for workstation/server use.

    That's what I am not getting. The Asus manual specifically states that these x16 slots don't deliver x16 electrical lanes to all the slots all the time.

    Thanks again in advance for any further clarification.
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