There is Marty 1 and Marty 2. There is zero functional difference between the two. Even the motherboards are radically similar.

Marty has a 386SX Processor, 2MB of RAM that is not upgradable, one floppy drive and a problematic CD ROM drive. It only outputs composite and S-video and it's impossible to modify for RGB output.

Marty 1

Marty 2

TC-MARTY is a special edition Marty that is more unobtanium than virgin's breastmilk.
In all seriousness it's quite rare. It was meant to hookup to a scanner and use a special SRAM card with a form of internet access. In the rear there is an attachment meant to hookup to a scanner/printer peripheral.