Photoshop Scratch Disk Full? How to Fix on Windows

If Photoshop shows a “Scratch Disks Full” error or runs slowly on Windows, the fix is to free up space on the drive designated as the scratch disk, move the scratch disk to a faster or larger drive, or clear Photoshop’s cache files. This article explains what the scratch disk is, why it fills up, and the exact steps to fix it on Windows 10 and 11.

What Is the Photoshop Scratch Disk?

The scratch disk is a reserved portion of your hard drive or SSD that Adobe Photoshop uses as virtual memory. When your computer’s RAM is full, Photoshop writes temporary data—like image history states, undo steps, and large filter calculations—to this disk. It is not a separate physical drive; it is simply a designated space on an existing drive.

By default, Photoshop sets the system drive (usually C:) as the scratch disk. This works fine until the drive runs low on free space, or when you work with very large files (e.g., 1 GB+ PSDs, 3D renders, or high-resolution panoramas).

Why Does the Scratch Disk Fill Up?

• Low free space on the designated drive: Photoshop needs at least 10–20 GB free to work comfortably, more for large documents.
• Too many history states: Each undo step stores a copy of the image, consuming scratch space.
• Cache and temp files accumulate: Photoshop leaves behind temporary files if it crashes or is forced to close.
• Large file sizes: Working with 8K images, HDR panoramas, or 3D layers can quickly exhaust available space.
• Multiple drives set as scratch: If you have several drives, Photoshop uses them in order; a full primary scratch disk can cause errors even if others have space.

How to Check and Change the Scratch Disk in Photoshop

1. Open Photoshop. If it won’t start due to the error, hold Ctrl+Alt (Windows) immediately after launching to open the Scratch Disk Preferences dialog before the main window loads.
2. Go to Edit > Preferences > Scratch Disks (Windows).
3. In the dialog, check the boxes next to the drives you want to use. Uncheck the system drive (C:) if it is low on space.
4. Set the order of preference using the up/down arrows. Photoshop fills the first disk, then moves to the second, and so on.
5. Click OK and restart Photoshop for changes to take effect.

For best performance, choose an internal SSD with at least 20% free space. Avoid using a USB flash drive or a network drive, as they are too slow.

How to Free Up Space on the Scratch Disk

If you cannot change the scratch disk (e.g., you have only one drive), free up space on that drive:

• Delete temporary Photoshop files: Go to C:\Users\[YourUsername]\AppData\Local\Temp and delete files named Photoshop Temp or ~PST####.tmp (only if Photoshop is closed).
• Clear Photoshop’s cache: Edit > Purge > All (this clears history states and clipboard data, freeing scratch space immediately).
• Move large files to an external drive or cloud storage.
• Run Disk Cleanup (search “Disk Cleanup” in Windows) to remove system temp files and old Windows updates.
• Uninstall programs you no longer use.

Preventing the Scratch Disk Full Error

• Keep at least 20–30 GB free on your scratch drive at all times.
• Reduce history states: Edit > Preferences > Performance and lower “History States” from 50 to 20 or fewer.
• Increase RAM allocation to Photoshop (Preferences > Performance) so it uses less scratch space, but leave at least 2–4 GB for Windows.
• Save and close large documents when not in use.
• Restart Photoshop periodically to clear temporary files.

Common Problems and Solutions

Problem: Photoshop says “Scratch Disks Full” but the drive has plenty of free space.
Solution: The scratch disk may be set to a drive with limited space, or the file itself is too large for the available RAM and disk. Check the scratch disk preference and ensure the drive with free space is selected. Also, try purging history states.

Problem: Photoshop is slow even though the scratch disk has space.
Solution: The scratch disk might be on a slow HDD. Move it to an SSD. Also check that you have enough RAM (16 GB minimum for heavy work) and that Photoshop is using 70–85% of it.

Problem: I can’t start Photoshop to change preferences.
Solution: Hold Ctrl+Alt when launching Photoshop to open the Scratch Disk Preferences dialog before the main window loads. You can also press and hold Shift to reset preferences (but this loses custom settings).

Frequently Asked Questions

Can I use an external drive as a scratch disk?

Technically yes, but it is not recommended. USB drives (even USB 3.0) are much slower than internal SSDs, which will make Photoshop lag when working on large files. Use an internal SSD or NVMe drive for best performance.

How much scratch disk space do I need?

As a rule of thumb, Photoshop needs 5–10 times the file size of your largest image. For a 1 GB PSD, you should have at least 10 GB free. For professional work with huge files, 50–100 GB free is safer.

Does clearing the scratch disk delete my work?

No. The scratch disk contains temporary data (history states, cached previews) that is not saved in your PSD. Clearing it will not delete your saved files. However, you may lose unsaved changes if you purge history states.

Why does Photoshop use the C: drive even if I selected another drive?

Photoshop always uses the system drive for some temporary files (like the “Photoshop Temp” file) regardless of your scratch disk setting. If C: is full, you may still see errors. Free up space on C: or move your Windows page file to another drive.

Can I set a folder as a scratch disk instead of a whole drive?

No. Photoshop only allows selecting entire drives or partitions, not specific folders. You can create a dedicated partition for scratch space if needed.

Does upgrading RAM eliminate the need for a scratch disk?

More RAM reduces how often Photoshop needs to use the scratch disk, but it does not eliminate it entirely. Very large files or complex operations (like 3D or video) still require scratch space. Even with 64 GB RAM, a scratch disk is necessary for stability.

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