Question about motherboards with integrated LAN

Posted on 2006-05-16
Last Modified: 2010-04-25
I have a couple of PCI based Firewire cards that I need to install on my motherboard.  The Firewire manufacturer suggests that I use as little of the PCI bus as possible for other devices such as LAN cards, modems, or sound cards.  

My question is do motherboards with integrated network cards (LANs) use the same PCI bus as the PCI slots themselves or do integrated devices use a different bus altogether for communication?  Is there some documention or a white paper out there that could explain the communication paths of these different integrated devices?  Thanks.
Question by:fourjohn
    LVL 42

    Expert Comment

    integrated LAN do not use PCI bus because they are not PCI cards.  they are part of the motherboard (thus, integrated).  if you open up a computer with an integrated LAN, you can see this.  the LAN connection is an extension of the motherboard... it is not in any kind of slot like PCI.
    LVL 1

    Author Comment

    Zephyr hex, I understand the physical placement of the integrated LAN may not be near the PCI slots, but I'm not so sure they use seperate buses.  Data still needs to flow along some bus or channel to and from the integrated component, just as would a device plugged into a PCI slot.  

    From my understanding there are at least 3 or 4 buses - ISA, PCI, AGP, and PCI-E.  Each bus has an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go.  They also operate at two different sizes of 16 or 32-bits and at different bus speeds measured in MHz.

    I'm thinking that integrated components do eventually share a bus path to communicate with the rest of the system.  And if so, which one?  Or are integrated components somehow directly wired along an isolated channel to communicate with the rest of the components?

    Hope that clarifies my question.  Thanks.
    LVL 31

    Expert Comment

    I *think* that the PCI bus incorporates at least some of the integrated components, like NIC, IDE controller, sound, even on-board video. I'm prepared to stand corrected, of course.
    LVL 69

    Accepted Solution

    You may want to look at this diagram:

    An integrated gigabit NIC would use up all the 133Mbyte/sec bandwidth of the PCI bus, so I think that example shows that an integrated LAN operates on a different bus than the PCI.
    LVL 24

    Expert Comment

    Ditto Rid's: I'm prepared to stand corrected...

    You've got internal and external buses, the former are faster. Memory (ram) for example is not ISA. With ISA slots and onboard NICs, none of the NIC jumper possibilities were excluded, and similarly for modem. VGA does not use that external bus, whether on board or a daughter card. OK, it did, and cards like mine may use AGP, while others may be allowed to use PCI. Sound cards can be added to ISA or PCI. If they are that slow, maybe they are on same old bus.

    > The Firewire manufacturer suggests that I use as little of the PCI bus as possible for other devices such as LAN cards, modems, or sound cards.  

    Try using BIOS to disable all of them. See if the edit window provides any more information on it
    LVL 1

    Author Comment

    The front side bus (FSB) connects the CPU to the northbridge.

    The back side bus connects the CPU with the level 2 (L2) cache.

    The memory bus connects the northbridge to the memory.

    The IDE or ATA bus connects the southbridge to the disk drives.
    The AGP bus connects the video card to the memory and the CPU.
    The PCI bus connects PCI slots to the southbridge.

    Does the integrated LAN operate on a seperate bus (from the PCI bus) called the LAN bus then?
    LVL 69

    Expert Comment

    That is what the pc block diagram seems to say.
    LVL 1

    Author Comment

    Thanks to Callandor for having the most definitive answer so far!  -John

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