The A500... Hmmm IIRC that extra memory was bogo memory (or some such name), and actually fitted into the custom chip address space... um... maybe it did configure as fast ram, I wish I still had an A500 to test it with :-(
From what I can remember it was known as pseudo fast RAM. In that it ran the same speed as chip memory. I can't remember what memory range it sat in though but;
I remember doing a small HW hack with cutting and soldering a few lines on the motherboard which then converted the 512k expansion into an extra 512k of Chip (giving you a total of 1meg Chip) which was great if you had a HD attached to the side of the machine.
