What is the
difference between the 100A, 100B, and 100+ Rainbows ? 
 The 100A could read only
disks that used its own proprietary format. The
 100+ could read, but not write to, PC-format disks. The 100B was a 
 
That's a software difference, and an important one from a user standpoint,
but it is not a difference in the hardware.