The CBM 500 is similar to the CBM 600 and CBM 700 machines.
The schematic diagram (4256041) says "PET-II" and "P500".

The whole machine is similar to the CBM-II (C600, AKA B128):

 - it has 128k or 256k RAM (located in bank 0,1 or 0-3)

 - it has a 6509 CPU with its banking scheme (esp. the I/O in bank 15)

This machine seems to have quite some oddities:

 - it has a VIC-II and thus runs at 1MHz

 - The VIC-II has access to 1k/8bit of video RAM and 1k/4bit of
   color RAM and a fixed 4k charrom.

 - However, there is a special 64k RAM bank that is "powered by VIC".
   From the FPLA equations that come with the schematics it seems that 
   by setting special output lines (CA and CB on the IEEE488 TPI)
   one can make the VIC use this 64k bank, that seems to be located
   in bank 0.
   This seems to be useable for hires graphics.

This information was provided by André Fachat (fachat@physik.tu-chemnitz.de).