I bought a new iMac with the latest operating system OS X 10.8.5 Mountain Lion. The Apple guys transfered all my files over for me (so I didn't do anything wrong there). I have had the new comp up and working for 5 days and already I have had the flag come up that says "Your Mac OS X startup disk has no more space availble for application memory. To avoid problems with your computer, quit any applications you are not using. Closing windows and removing files from your start up disk will also help." I took the Mac in and they checked the hard drive and I have scads of memory unused. So they think that the Photoshop I had open during these flag times had to be the culpret. Anyone know what I can do about it? Do you think it was Photoshop saving files in the background? I did not think that Photoshop saved files in the background. Help.
If you got to your Preferences under the File Handling section, you will see a check box for saving files in the background, as well as a check box that controls whether Photoshop automatically saves a backup of what you are currently working on. You can shut both of these off, but you must then remember to save your work frequently while working, lest a power outage, crash, or some other disaster cause you to lose all your recent work. It's safer to have these both turned on if you are at all concerned about losing your work.
Photoshop will also write out temporary data to disk if it has insufficient RAM to handle the current image (or images) you are working on. The setting for that is under the Performance section of your Preferences dialog. Check to make certain the Scratch Disk is pointing to a hard disk that has plenty of room. There are other settings here that can reduce the amount of hard disk space potentially used, but messing with those without knowing exactly what you are doing can cause serious performance issues.
Last, but not least, if indeed the problem is that Photoshop needs to write to the hard disk, then it will help to make sure you close any images you are done working on. Don't leave a whole bunch of images open unless you are sure Photoshop will have the RAM to handle them all.