Here’s an option for detecting the type/size of memory already installed in your system without having to open your computer. This Tool is also helpful so you can easily check other specification on your system.
Download "System Information for Windows Tool" HERE... or visit their site.
This useful free application/tool should be a standard in any geek’s toolkit. It comes bundled as a single file, no installation required.
Once you open it up, navigate to Hardware and then Memory on the left-side panel, you’ll see what type of memory is already installed in your computer.
See pic below, looks like my DESKTOP system can support up to 4GB of memory and I got a total of 1.5GB memory already installed. I have two memory module... on the first slot, I have 1GB DDR2-667 module and 512MB DDR2-667 module on the second slot.
CLICK THE IMAGE TO ENLARGE
This tool also lets you know that you need the SODIMM form factor memory if you run it on LAPTOP...it shows 1GB DDR2-533 SODIMM memory module.