74 Removing and Installing Parts
www.dell.com | support.dell.com
Addressing Memory with 4-GB Configurations
If you u se opti onal me mory ri ser boa rds and eight, 512-MB RIMMs, you can
install 4 GB of physical computer memory. Current workstation-class OSs
(such as Microsoft® Window s 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.