Reduction in Available RAM
Pretty certain that the Available RAM under Memory Usage of the Performance tab, in my Photoshop CS6 (64 bit) running in 64 bit Windows 10, used to be much closer to the installed 8GB, though less than that figure.
However, it now seems to be only 3337 MB. Not really sure when this change took place. Last time I was doing some intensive Photoshop work was...actually back a the start of the week, Monday 28th May and I'm pretty sure I would have whacked the "Let Photoshop Use:" amount up quite a bit and don't remember thinking, "Oh, why only 3337 MB"
Just done a Windows Memory Diagnostic check which showed no errors. Will try another more thorough RAM check in a moment. Below is some memory info in the Task Manager. Any one else experienced this?

