I recently discovered that I oly had 5 GB of storage left on my 250 GB MacBook Air OS 10.7.5. I moved my photo's to an external HD and now have 17 GB. The storage graph says that 207 GB are being used under the 'Other' category. DaisyDisk says 137 GB are being used in 'cores'. How do I get my storage space back? What is 'cores'?