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PCI to PCI
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PCI to PCI |
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Acies
Moderator
Member Rara Avis
since 2000-06-07
Posts 7665Twilight Zone |
Just wondering exactly what a PCI to PCI bridge is. Can enyone explain please?  |
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Ron
Administrator
Member Rara Avis
since 1999-05-19
Posts 8669Michigan, US |
PCs are following the evolultionary path of the mainframes, becoming not a single CPU but rather a "team" of CPUs working together. When the team exists entirely on the motherboard, they can talk to each other efficiently, limited only by the internal bus speed. But when you "add" a new CPU to the team, usually by installing a new adapter card, they have to talk to each other across the much slower PCI bus. PCI has physical and logical constraints which limit its ability to efficiently scale to support the large numbers of high-speed processors and peripherals required for the high-performance real-time market. On the physical side, PCI has electrical and mechanical constraints to ensure signal integrity. These include limits on loading, trace lengths, and connectors. These limit a single PCI-bus segment to a total of 10 loads, with connectors considered as two loads each. Thus, a motherboard or passive backplane typically has a limit of four plug-in boards on a single PCI-bus segment. PCI-to-PCI bridge chips extend I/O support capability by enabling motherboard designers to exceed the four-slot PCI bus limitation for PCI devices and option cards. Each PCI-to-PCI bridge chip added to the motherboard creates a new PCI bus to support additional PCI slots or devices. A PCI-to-PCI bridge also enables adapter card designers to overcome the single load limitation of the PCI Specification by providing an independent PCI bus on the adapter card, to which as many as nine more devices can be added. PCI-to-PCI bridges simplify the configuration of intelligent I/O subsystems such as RAID controllers and the interconnection of independent processors in communications and embedded PCI applications. The new devices enable local processors to manage configuration of PCI subsystem devices without host intervention. The Bridges effectively "hide" subsystem resources from the host processor and allows an entire subsystem to appear to the host processor as a single device requiring only one device driver. The local processor can then independently initialize and control the subsystem, simplifying overall system configuration and freeing the host processor from subsystem device control tasks. |
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Acies
Moderator
Member Rara Avis
since 2000-06-07
Posts 7665Twilight Zone |
Ron --- Do you mean that by physically looking at a motherboard and there is more that 4 PCI slots, we can assume that the board does have a PCI to PCI bridge? If so, how do you know which PCI slots are the ones supported by the so called bridge? maybe I'm not making any sense here  ps. ya like me new sig?  [This message has been edited by Ron (edited 01-01-2000).] |
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Ron
Administrator
Member Rara Avis
since 1999-05-19
Posts 8669Michigan, US |
If the motherboard supports more than four slots, it almost certainly is using a Bridge to do so. Unfortunately, it's even more complicated than that. Some new motherboards are supporting the 66mHz PCI bus, rather than the original 33mHz, and that cuts the specs in half. So, if a motherboard includes more than two slots, it "might" be using a Bridge. Just by looking at the motherboard, I know of no way to tell which slots are which. Used to be, it didn't really matter. Those running off the Bridge would be no different than those directly attached to the motherboard. If you're running a new operating system, however, like Windows 2000, it just might matter. When you turn on Windows 2000, the OS asks each adapter for some very important information. It assumes that information won't change until the machine is physically powered down and back up. Some of the Bridges, unfortunately, don't adhere to this assumption. The reason I bolded the word "physically" is because the new "sleep" mode is a non-physical powering off of the computer. And some Bridges will awaken from sleep mode with NEW information, which Windows 2000 will never see. Ergo, the adapter stops working properly and it can even freeze Win2000 in the process. The solution is to either disable sleep mode or, better, put the adapter in a non-Bridge PCI slot. As far as I know, the latter solution is a matter of trail and error.  Your new signature is at least better than the last. |
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