One way to expand the functionality and memory of the XO laptop is by installing an SD (Secure Digital) card in the expansion slot of the machine. This slot is located under the right side of the screen. Twist the screen halfway around, and you can see the slot.
You can use any kind of SD card for this machine. While some devices won't work with SDHC cards, the XO will work just fine with them.
The theoretical maximum size card the XO can accept is 64 gigabytes, so anything you buy on sale will work just fine.
You can find good pricing on SD cards by accessing this website:
Click on your state and then click on the Flash Memory link to see what's on sale this week.