The Commodore Model II series came out in a few major models:

 - The C5x0 had a VIC-II video chip (as the C64) and ran on 1 MHz
  
 - The C6x0 had a CRTC video chip for 80 columns display and ran on 2 MHz
   The character size is 8x8. It came in a Low-Profile case.

 - The C7x0 is basically the same as the C6x0. Only the CRTC is initialized
   for 14x8 pixel character size. The kernal (as well as the basic!) 
   is the same as the C6x0, only two resistors at an I/O port determine the 
   way to initialize the CRTC. It came in a high-profile case with separate 
   keyboard similar to the late PET models.

The x10 Models (C510, C610, C710) have 128k RAM, the x20 Models (C520, C620
and C720) have 256k RAM. For each RAM size a different BASIC ROM is 
necessary. The C610 and C710 models as well as the C620 and C720 models 
use the same ROMs, however.

There were supposed to be C630 and C730 models with 256k RAM and a
coprocessor, although their fate is unknown.

In North America the models were known as "P500" (C5x0), or
"B128" (C6x0) and "B256" (C7x0), or "BX256" (C630/730).


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