and 640 MB under 32-bit Windows. This value is indicated in the About dialog.

That's what I'm confused about. My About window shows 1 GB Max.

Caution : I think that if you run a 32-bit Windows system on a 64-bit processor, Windows will let programs run in 32-bit mode only.

This is correct. I'm fully aware of that. [;)]
It was the best suited processor available for my motherboard, for my needs at the time, way back when I built this rig about 7 years ago.