The GR-77B is a fully analog 4 voice polyphonic synthesizer and
shares the same internal electronics as the Roland JX-8P keyboard.
The synth can store 64 sounds internally (in 8 banks of 8).
Another 32 sounds can be stored and retrieved externally in proprietary Roland PC-16M memory cartridges.
 

The inputs on the back of the unit are as follows (from left to right):
POWER - Power Switch (top)
AC INLET - Power Cord (bottom)
MEMORY CARTRIDGE - M-16C Memory card holder
GUITAR INPUT - Guitar/Bass input connector
PROGRAMMER - PG-800 programmer connector
MIDI OUT - MIDI OUT connector
MEMORY PROTECT - Memory protect switch
PITCH - Pitch control jack (optional external pedal)
VCF - VCF control jack
GUITAR OUT - Guitar/Bass magnetic pickup output jack
OUTPUT - Line out jacks
LEVEL - Level selector switch
OUTPUT (2) - XLR output connectors