That's because not all of your free space on a hard drive is assigned as scratch disks for Photoshop. Some of you may notice that Photoshop shows scratch disk is full even when there is a lot of free space on your computer. When there is no room in both the RAM and the scratch disk for the Photoshop temporary files, the 'scratch disk full' error is triggered.
When you are opening or working on a huge project in Photoshop, there could be lots of temp files. What is a scratch disk? A scratch disk on PC/Mac is the hard drive that Photoshop use as virtual memory to store temporary files when there is not enough RAM for the temp files. Why Is Photoshop Saying My Scratch Disks Are Full? Why Is Photoshop Saying My Scratch Disks Are Full?.
