dell memory upgrade

I have a refurbished Optiplex GX620 that came with 1GB of RAM. I upgraded the unit by installing two 1 GB DELL sticks.

My question is, can I also re-install the 1 GB of memory that came with the machine (in a different slot) to give me 3 total GB?

 

Okay, let me make sure I got this. If I pulled a 1GB stick out and put in two 1 GB sticks, it's okay to re-install the "old" 1 GB stick to give me 3 GB?

But, if I pulled out two 512MB sticks, then put in two 1 GB sticks, it's not okay to put the two 512 MB sticks back in?

I say this because I have another Optiplex at my office that I pulled out two 512 MB sticks. There are 4 slots in this computer.

Thank you very much for your help and information, Halo.

 

The second option is the better one. It will keep your system in dual channel, which eliminates "data lag" when your computer uses the memory. Always use dual channel above single channel, if you can.

If it was my computer I'd add the two 512MB modules and be happy with 3GB dual channel