I keep getting a pop up ling me my start up disc is full. To my knowledge I have an external hard drive I keep my photos and music on. I have no idea what else to do.
MacBook Pro with Retina display, OS X Mavericks (10.9)
You need to examine the contents of your hard drive to see what is taking up all the space. You need to maintain a minimum of 10 - 15 GB of empty space on your hard drive at all times in order for the OS to work properly.
FWIW, when you move photos or videos from your internal to your external, do you then trash the ones on the internal and empty the trash?
Also, do you use Time machine?
http://pondini.org/OSX/DiskSpace.html
free up some space on my start up disc
