Keyboard (all hail the Model M!)

Memory (error handling, presence detect)

Mouse (YMMV)

Optical Wireless Mouse  

Parallel Port (Modes, ExpressPrint)

Troubleshooting (an attempt)

Errors (beeps, general, SCSI, IML)
   Advanced Diagnostics Error Codes (QEET starts with "9")

Microchannel Components (watchdog, Int4b, System Registers, etc)