Where to find the scratch disk setting in Photoshop

The scratch disk setting lives in Photoshop's preferences, not in a menu you'd expect. On Windows, go to Edit > Preferences > Performance. On Mac, go to Photoshop > Settings > Performance. The Performance panel is where Photoshop shows you which drive it's currently using and lets you change it.

You'll see a list of drives under the heading "Scratch Disks". Photoshop assigns them in order of priority — the top drive is primary, the second is secondary, and so on. A checkmark means the drive is active. An X means it's disabled. You can have multiple scratch disks running at once, which Photoshop uses when the first one fills up.

Key Takeaways

  • Scratch disk settings are in Preferences > Performance on Windows or Settings > Performance on Mac, not in the main menu.
  • You can assign multiple drives as scratch disks, and Photoshop will use them in the order you set, moving to the next when one fills up.
  • The best scratch disk is a fast, separate drive that is not your system drive and has at least 20 to 40 gigabytes of free space.
  • After you change the scratch disk, Photoshop must restart before the new setting takes effect.
  • If Photoshop freezes or runs slowly, a full scratch disk is often the cause — clearing it or adding a new one usually fixes the problem.

Why you might need to change your scratch disk

Photoshop uses a scratch disk as temporary storage when your computer's RAM runs out. Every time you open a large file, explore a filter, or undo a step, Photoshop writes data to the scratch disk. If that disk is slow, full, or the same drive as your operating system, Photoshop slows down or freezes.

The default scratch disk is usually your C: drive on Windows or your Macintosh HD on Mac — the same drive your operating system lives on. This is the worst place for it. Your system drive is already busy handling Windows or macOS, running background programs, and storing your files. Adding Photoshop's temporary data to that load creates a bottleneck.

If you have a second hard drive, an external SSD, or a fast USB drive, moving the scratch disk there can cut Photoshop's lag time in half. The faster and emptier the drive, the faster Photoshop works.

How to select a new scratch disk

In the Performance preferences, you'll see all the drives connected to your computer listed under "Scratch Disks". Click the checkbox next to the drive you want to use. If you want to use multiple drives, check the boxes for all of them — Photoshop will fill the first one, then move to the second when it's full.

Uncheck the box next to your system drive (C: or Macintosh HD) to remove it from the scratch disk list. If you have an external SSD or a second internal drive, that's the ideal choice. The drive must have at least 20 to 40 gigabytes of free space for Photoshop to work smoothly, depending on the file sizes you work with.

After you've selected your new scratch disk, click OK. Photoshop will ask you to restart the process. Close Photoshop completely and open it again — the new scratch disk will be active once it restarts.

What to do if your scratch disk is full

If you see a message saying "Scratch disk is full", Photoshop has run out of temporary storage space. This usually means your chosen scratch disk doesn't have enough free space left. The fastest fix is to add a second scratch disk or move to a different drive with more room.

You can also clear the scratch disk manually. In Photoshop, go to Edit > Purge > All on Windows, or Photoshop > Purge > All on Mac. This deletes all the temporary data Photoshop has stored. You'll lose your undo history, but Photoshop will free up space when ready.

If you keep hitting this error, your scratch disk is too small for the work you're doing. Add a second scratch disk, or move to a larger drive. Check how much free space you have on your current scratch disk — if it's less than 10 gigabytes, Photoshop will struggle.

Choosing between internal and external drives

An internal second hard drive is faster than an external one, but an external SSD is faster than an internal mechanical hard drive. The speed matters because Photoshop reads and writes to the scratch disk constantly while you work.

If you have a second internal drive (SATA or NVMe), use that. If you only have one internal drive, a USB 3.0 or Thunderbolt external SSD is your next best option. Avoid USB 2.0 drives — they're too slow and will make Photoshop slower than using your system drive.

External drives have one advantage: you can unplug them and take your scratch disk with you. If you work on multiple computers, you can carry a fast external SSD and set it as the scratch disk on each machine. Just make sure it's plugged in before you open Photoshop, or Photoshop will revert to your system drive.

Setting up multiple scratch disks in order

You can assign up to four scratch disks in Photoshop. The order matters — Photoshop fills the first one completely before moving to the second. To change the order, click on a drive name and use the up and down arrows to move it higher or lower in the list.

A typical setup is: primary scratch disk (a fast external SSD or second internal drive), secondary scratch disk (another external drive or your system drive as a last resort). Photoshop will use the primary drive for most work and only switch to the secondary when the primary is nearly full.

If you have three or four drives, put your fastest drive first, your second-fastest second, and so on. This keeps Photoshop working at top speed as long as possible. Once you've set the order, click OK and restart Photoshop.

Troubleshooting slow performance after changing the scratch disk

If Photoshop is still slow after you've switched to a new scratch disk, the new drive may not be as fast as you expected, or it may not have enough free space. Check how much free space is left on your scratch disk — right-click the drive in File Explorer (Windows) or Finder (Mac) and select Properties or Get Info. If it's less than 20 gigabytes, Photoshop will slow down.

If the drive has plenty of space, the drive itself may be the problem. External USB 2.0 drives, older mechanical drives, or drives that are already being used heavily by other programs will all slow Photoshop down. Try a different drive, or check whether the drive is being accessed by backup software or antivirus scans while you're working.

You can also check Photoshop's memory usage in the Performance preferences. If you see a red bar next to "RAM", Photoshop is using all your available memory and relying heavily on the scratch disk. Adding more RAM to your computer is the long-term fix, but switching to a faster scratch disk will help when ready.

Frequently Asked Questions

Can I use a USB flash drive as a scratch disk?

Technically yes, but it's not recommended. USB flash drives are much slower than hard drives or SSDs, and they have limited write cycles — using one as a scratch disk will wear it out quickly. A USB 3.0 external SSD is a better choice if you need portability.

What happens if I unplug my external scratch disk while Photoshop is running?

Photoshop will freeze or crash. Always make sure your external scratch disk is plugged in and stays plugged in while you're working. If you need to unplug it, close Photoshop first and change the scratch disk back to your system drive in Preferences.

Do I need to restart my computer after changing the scratch disk, or just Photoshop?

You only need to restart Photoshop, not your entire computer. Close Photoshop completely and open it again. The new scratch disk will be active on the next launch.

Can I set my network drive as a scratch disk?

No. Network drives are too slow for Photoshop to use as a scratch disk. Photoshop needs a local drive — either internal or directly connected via USB or Thunderbolt. Network latency will make Photoshop unusable.

How much free space should my scratch disk have?

At least 20 to 40 gigabytes, depending on the file sizes you work with. If you regularly open files larger than 500 megabytes or work with many layers, aim for 50 gigabytes or more. Check your drive's free space regularly and add a second scratch disk if the first one drops below 10 gigabytes.