Scratch Disk |
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What exactly *IS* a scratch disk? |
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| The General Meaning A scratch disk is any space set aside for temporary storage. This could be in the form of a single temporary file, (called a scratch file), a certain portion of a hard disk (called a scratch disk), or an entire hard disk (also called a scratch disk, or sometimes a scratch drive). The duration of storage can vary. Programs like Photoshop might use the storage for only a few seconds while performing a complex operation, and then clear the space again. When engineers repair important computer systems however, sometimes entire systems will be backed-up on a separate hard disk, in case anything goes wrong, and restored at the end if necessary. The main thing to remember is that scratch space is never used to permanently store files. The actual location of the space used is often different each time a program is run. The Photoshop Meaning In the world of Photoshop, a scratch disk refers specifically to a portion of disk space used for temporary storage. This allows Photoshop to perform operations requiring more memory than is available from the system RAM. Photoshop uses the space by creating temporary files, and then deleting them after they are no longer needed. It names the files using the format “~PST####.tmp”, where “####” represents four numbers. Placing the Photoshop Scratch Disk The Photoshop scratch disk can be moved to a location which best suits your system. You might have multiple hard disks or disk partitions, and if so moving the scratch disk can improve performance. To alter the scratch disk location, go to 'Edit - Preferences - Plug-Ins & Scratch Disks'. Using the four drop down boxes in the dialog that appears, pick the disk drives you want Photoshop to use. For best performance, use a drive that does not contain your operating system (This is C:\ for most systems). Preferably it should also not contain virtual memory, or the Photoshop or Photoshop Elements program files. Don't use network drives or removable media drives for scratch disks. Some users dedicate an entire partition to scratch files, but this is not necessary for most people. Pick a drive with plenty of free space though, and preferably the fastest drive if they are of different speeds. Adobe recommends that you defragment the scratch disk(s) regularly, to improve performance. The Most Common Problem Now so far, this is all well and good. But problems can arise if Photoshop crashes, or does not shut down properly. When this happens, sometimes not all the scratch files that are created are deleted, so some of the scratch space is never reclaimed. If you are experiencing this problem, take a look at my article on what to do when you see the 'Scratch Disk is Full' error message. How Photoshop Allocates Memory If you are interested in the technical details of how Photoshop reserves and uses memory, then read on. For most people, just knowing what a scratch disk is and what purpose it serves is sufficient, but if you wish to know in more depth how Photoshop handles memory, read my article on Photoshop Memory. |
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A page about the Photoshop Scratch Disk
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