Dell Dimension 8250 - Manual (Page 17)

RDRAM technology requires that all memory connectors have either a memory module or a continuity module installed. Memory modules and continuity modules
are easily identified—memory modules have a metal cover on one side of the module and continuity modules do not.
Memory modules are the actual components that provide memory for the microprocessor; continuity modules are used only to complete the memory circuit if
memory modules are not installed in all of the memory connectors.
Another RDRAM requirement is that memory modules must be installed in pairs of matched memory size. This means that if you purchased your computer with
128 MB of memory installed and you want to add another 128 MB of memory, you must remove the two continuity modules and replace them with two 64-MB
memory modules.
The only two valid memory configurations are:
l A pair of matched memory modules installed in connectors RIMM1 and RIMM2 with continuity modules installed in connectors RIMM3 and RIMM4
or
l A pair of matched memory modules installed in connectors RIMM1 and RIMM2 and another matched pair installed in connectors RIMM3 and RIMM4
Removing a Memory Module
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 the new modules were purchased from Dell. Your original memory modules must be installed as a pair in either connectors RIMM1
and RIMM2 or RIMM3 and RIMM4. Do not pair one original memory module with one new memory module in connectors RIMM1 and RIMM2 or RIMM3 and
RIMM4. Otherwise, your computer may not start properly.
HINT: The metal cover on a memory module is manufactured in various colors. The color of the metal cover has no effect on the module's performance.
NOTICE: You can only install continuity modules in connectors RIMM3 and RIMM4.
HINT: Mixed pairs of PC1066 and PC800 modules all function as PC800.
HINT: Memory purchased from Dell is covered under your computer warranty.