To use memory efficiently Linux reserves memory buffers and cached memory. This is, it reserves memory ahead of time so it's ready when you need it. (e.g. your most used application or the data you are working with)
You can see that if you execute 'top' from the command line or "Start | Control panel | Top view running processes".
On the top left It says that it's using almost all the memory, even when you know that you don't have any apps running. On the same line you will see how much is reserved for buffers and cached memory.
If you subtract the memory buffers in torsmo, you get a real picture of how much available RAM you have.