For PCI and PCIe devices, a BAR is a Base Address Register that is used by the BIOS or OS to tell the device what physical addresses to map its memory resources into. Most PCI devices in your system requests a certain amount of memory space, and the BIOS tries to fit them all below 4 GB in order to ensure compatibility with 32-bit operating systems. It sounds like your computer has 4 GB of RAM and that both video cards contain large amounts of RAM.
In those error messages, the location of the device is specified as bus/device/function. I have access to a Dell Precision 390 and it appears that all of the onboard devices on that system are on PCI bus number 0, so your errors probably refer to a device that you have plugged into a PCI or PCIe slot. Each PCIe slot gets its own bus number, so bus number 5 might actually correspond to a multi-function PCIe device such as a sound card or video capture card.
You should be able to track down which devices are 4/0/0, 5/2/0, 5/4/0, and 5/5/0 once the OS is loaded, if the BIOS doesn't print this information before booting. (Note that this assumes that the OS doesn't reassign the PCI bus numbers on boot, which would destroy the evidence; if that happens, the OS may be patching up the mess that the BIOS left.)
If you use Windows, you can find the PCI bus/device/function numbers of a device by right clicking on it in Device Manager, selecting
Properties..., and looking at
Location: on the
General tab. (On Vista and Windows 7, this same information also shows up when you select the
Details tab and choose
Location information from the
If you use Linux, you can find the PCI bus/device/function numbers using the