Dell's on-line support site is one of the best:
http://support.dell.com/us/en/home.asp

Go to this site and plug in your specific model number.  Click on
"Specifications" after arriving at the next page dedicated to your model.
You should find that you can use "32 bit, nonparity, EDO or fast-page mode".
You can click on "Tech Notes/Memory" for more details about matching, etc...
The system ships with 60ns, non-parity, EDO, 72pin SIMMs.

> My in-laws have a Dell Opti-Plex 166mhz pentium . They need to add more
RAM
> but don't have a clue what type to get. I need to know what type and how
> many pin RAM to buy.Any help would be greatly appreciated.
>

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