Dell OptiPlex GX280 - Manual (Page 81)

A matched pair of memory modules in connectors DIMM1 and DIMM2 (white securing clips)
B matched pair of memory modules in connectors DIMM3 and DIMM4 (black securing clips)
Addressing Memory With 4-GB Configurations
The small-desktop, desktop, small mini-tower, and mini-tower computers support a maximum of 4 GB of memory when you
use four 1-GB DIMMs. Current operating systems, such as Microsoft® Windows® 2000 and Windows XP, can only use a
maximum of 4 GB of address space; however, the amount of memory available to the operating system is 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 components require memory address space:
System ROM
APIC(s)
Integrated PCI devices, such as network connectors and SCSI controllers
PCI cards
At start-up, the BIOS identifies the components that require address space. The BIOS dynamically calculates the amount of
reserved address space required. The BIOS then subtracts the reserved address space from 4 GB to determine the amount of
usable space.
If the total installed computer memory is less than the usable space, all installed computer memory is available for use
only by the operating system.
If the total installed computer memory is equal to or greater than the usable address space, a small portion of installed
memory is available for use by the operating system.
Removing Memory
CAUTION: Before you begin any of the procedures in this section, follow the safety instructions in the
Product Information Guide.
NOTICE: If you remove your original memory modules from the computer during a memory upgrade, keep them
separate from any new modules that you may have, even if you purchased the new modules from Dell. If possible, do
not pair an original memory module with a new memory module. Otherwise, your computer may not start properly.
You should install your original memory modules in pairs either in connectors DIMM1 and DIMM2 or connectors DIMM3
and DIMM4.
NOTICE: If applicable, removing memory modules from DIMM2 and DIMM4 on the desktop computer requires you to
remove the optical drive (see section on Drives). Failure to do so may cause damage to the memory module and the
DIMM socket.