When your system does not have enough RAM to perform an operation, Photoshop and ImageReady use a proprietary virtual memory technology, also called scratch disks. A scratch disk is any drive or a partition of a drive with free memory. By default, Photoshop and ImageReady use the hard drive that the operating system is installed on as its primary scratch disk.
You can change the primary scratch disk and, in Photoshop, designate a second, third, or fourth scratch disk to be used when the primary disk is full. Your primary scratch disk should be your fastest hard disk, and should have plenty of defragmented space available.
The following guidelines can help you assign scratch disks:
- For best performance, scratch disks should be on a different drive than any large files you are editing.
- Scratch disks should be on a different drive than the one used for virtual memory.
- Scratch disks should be on a local drive. That is, they should not be accessed over a network.
- Scratch disks should be conventional (non-removable) media.
- Raid disks/disk arrays are good choices for dedicated scratch disk volumes.
- Drives with scratch disks should be defragmented regularly.