Hard Drive doesn't show up in the preferences menu when trying to assign it as a scratch disk.

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@defaultjb65t1s1whjk wrote:

...the hard drive is an HP 512 gigabyte SD card with no data on it.

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If my understanding is still current, Photoshop might not like the fact that it is an SD card, because it might consider it “removable.”

The current updated Adobe help article doesn’t seem to mention this, but I thought in the past it said that for the scratch volume, Photoshop does not support any volume it thinks is “removable.” It wants to minimize the possibility that the volume containing the virtual memory scratch file might disappear during the session, which might result in an error or crash. I say “minimize” and not “eliminate” because Photoshop does allow setting up a scratch volume on an HDD or SSD connected to an external port, even though those could also be unplugged in the middle of a session.

I just did a test. I mounted both an SD card, and a bare hard drive in an external USB drive dock. Technically, it’s just as easy to unmount either during a Photoshop session, but Photoshop  Scratch Disks lists the hard drive and does not list the SD card. Years ago I think Photoshop did not accept removable drive cartridges as scratch disks. So there seems to be something Photoshop can detect from the OS about whether the volume is considered “removable,” and it passes judgment based on that.

And yet…I just inserted a USB stick drive, and Photoshop listed it as a potential scratch drive. So maybe there is something about this I’m missing…