Dell Precision 390 - Manual (Page 61)

The recommended memory configurations are:
¡ A pair of matched memory modules installed in connectors DIMM_1 and DIMM_2
or
¡ A pair of matched memory modules installed in connectors DIMM_1 and DIMM_2 and another matched pair installed in connectors DIMM_3 and
DIMM_4
l If you install mixed pairs of DDR2 memory that run at different speeds, the modules function at the slowest speed installed.
l Be sure to install a single memory module in the DIMM_1 connector, the connector closest to the processor, before you install modules in the other
connectors.
l While installing memory modules, ensure that you do not mix ECC and non-ECC memory.
Addressing Memory With 4-GB Configurations
Your computer supports a maximum of 8 GB of memory when you use four 2-GB DIMMs. Current operating systems, such as Microsoft® Windows® XP, can
only use a maximum of 4 GB of address space; however, the amount of memory available to the operating system is 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:
l System ROM
l APIC(s)
l Integrated PCI devices, such as network connectors, SAS controllers, and IEEE 1394 controllers
l PCI or PCI Express devices/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.
l 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.
l 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.
Installing Memory
NOTE: Always install memory modules in the order indicated on the system board.
A matched pair of memory modules in connectors DIMM_1 and DIMM_2 (white securing clips)
B matched pair of memory modules in connectors DIMM_3 and DIMM_4 (black securing clips)
NOTE: Memory purchased from Dell is covered under your computer warranty.
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 DIMM_1 and DIMM_2 or
connectors DIMM_3 and DIMM_4.
NOTE: If you use a 64-bit version operating system, the entire memory range is available to the operating system.