Transparent bridges (a. k. a. HUB-to-PCI bridges)?
jhb at FreeBSD.org
Wed Nov 24 07:41:13 PST 2004
On Wednesday 24 November 2004 09:47 am, Chuck Swiger wrote:
> Scott Long wrote:
> > Chuck Swiger wrote:
> [ ... ]
> >> A host-PCI bridge is typically part of the "southbridge" chip of
> >> modern motherboards; on Intel motherboards this is also called the ICH
> >> chip, such as the 82801AA/BA/CA/etc. VIA Southbridges include the
> >> VT8233/8235/8237/etc.
> > Nope. The southbridge typically holds a PCI-ISA bridge. The host-pci
> > bridge is usually found in the northbridge part of the chipset. The
> > whole point it to bridge the CPU to one or more PCI buses.
> I've been wrong before, but please double-check diagrams like:
> The "northbridge", or MCH, connects to the CPU, AGP, RAM, and the
> The "southbridge", or ICH, connects to PCI, ATA, USB, BIOS chip, and the
> northbridge. Newer southbridge chips may add integrated LAN,
> 1394/Firewire, integrated AC'97 audio, and such via external codec chips
> like the VT6103 PHY.
The northbridge is the host-pci bridge. It contains a virtual PCI-PCI
bridge/bus that represents AGP. The chipset uses a propietary interconnect
to the southbridge such that the devices the north and south bridges connect
to show up as one pci bus (bus 0). You could build a system without a
southbridge (just PCI-X bridges or some such) and it would still have a
John Baldwin <jhb at FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve" = http://www.FreeBSD.org
More information about the freebsd-current