Pet 2001 w/ serial number < 100000:
- chicklet keys (with capital letters/graphics symbols on them); could swap in the lowercase letter forms at the cost of the graphics symbols
- integrated storage solution (built-in cassette player)
- integrated monochrome (white on black) monitor
Two pins in the user port were the output of a programmable timer. After I read about it in a magazine, a simple RadioShack amplifier wired across the connector provided "music". It had built-in BASIC _and_ a hardware monitor. Two languages in one little machine.
The _second_ computer I had was even cooler: a CompuColor II. The keyboard had custom colored keys so you knew how to set colors as you programmed. The monitor was a portable TV w/ the tuner replaced by a floppy disk drive. The HOURS that can be absorbed writing 16 (yes, 16!) color games in pirated MS-BASIC (or so the various history sites say; I don't know anything about where the BASIC came from). No format command so you were expected to buy disks from CompuColor; we got a huge box with the computer so we never needed any (100 disks at 50KB each? Who could need to store >5MB of information?).