Ok so a bit of explanation. You have only one core, with hyper-threading, so it appears to the OS as if you have 2 cores, but in reality you don't. What the 2 virtual cores do is let's say your computer is processing some information. Now, suddenly, it can no longer do so because it is waiting for some other info to come from the cache. However, there is something that is of lower priority that is ready to go. It will process that information in the "2nd" core. In reality what really is happening is one core can juggle back and forth between the first most priority and the second most priority. You are not only using one core because you are at 50% CPU usage (however, you are using your one and only core). It' just that your CPU is just running at 50% capacity to read and write from the HDD. Now, I have no experience with Intel's ATOM processors, however 50% seems a little high looking at its specs. What I am more suspicious of is your HDD. If it's old, it could be becoming worn out and this could be early indications of a HDD failure. I would back your data up.