Thanks for your reply Tomas.
Here’s one example, in point 8: https://www.schoolofmotion.com/blog/cached-preview
“Instead it is recommended that you separate your disk cache and project files across two separate drives. I typically have my project files on an external SSD and my disk cache on my local storage.”
By internal drive, yes, I mean the main OS drive. Based on the advice, I’m keeping all my project files/footage on the main/internal drive, and putting the cache on an external drive.
Now I need a replacement drive, and I’m wondering if the extra cost of going from HDD to SSD, and/or USB 3 to thunderbolt, is likely to be justified in terms of AE performance.