Dell 530 manual Addressing Memory with 4-GB Configurations, APICs

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Addressing Memory with 4-GB Configurations

If you use optional memory riser boards and eight, 512-MB RIMMs, you can install 4 GB of physical computer memory. Current workstation-class OSs (such as Microsoft® Windows NT® and Windows® 2000) can only utilize a maximum of 4 GB of address space. However, the amount of memory available to the OS will be slightly less than 4 GB.

Certain components within the computer require address space in the 4-GB range. Any address space reserved for these components cannot be used by computer memory. The following is a list of some components that require memory address space:

•System ROM

•APIC(s)

•Integrated PCI devices, such as the network adapter, SCSI controller, and IEEE 1394 controller

•PCI and AGP expansion cards

•The AGP Aperture size specified in system setup

At system start-up, the BIOS identifies the components that require address space. Starting at the highest end of the 4-GB range, it assigns those addresses working downward. All remaining addresses are then available for use by installed computer memory.

In other words, the BIOS dynamically calculates the amount of reserved address space required. It then subtracts the reserved address space from

4 GB to determine the amount of usable address space:

•If the total installed computer memory is less than the usable address space, all installed computer memory is available for use by the OS.

•If the total installed computer memory is equal to or greater than the usable address space, a small portion of installed computer memory is not available for use by the OS.

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