The whole System 100 consists of five components, the Synthesizer 101, the Expander 102, Mixer 103, Sequencer 104, and Monitor Speaker 109. Each component is relatively self-sufficient with its own power supply and housing. It was Roland's idea that someone would start out with the Synthesizer 101 and add on to it piece by piece.
This is a self-contained semi-modular synthesizer with a 37-note (F-F) keyboard. It features an ADSR, LFO, Portamento, a VCO (with pulse width modulation and a tuning knob marked in Hz from 10Hz to 10kHz), white or pink noise, an audio mixer (with sliders for VCO, Noise, and External Input), a high-pass filter, a low-pass VCF, and a VCA with input for LFO. There are also buttons for auto-glide and manual-glide and an A-440Hz tuning oscillator. All of this in 21 sliders, five knobs, 14 mini-jack sockets, seven switches, and three 1/4" jacks (for headphone and high and low outputs).
This is essentially a keyboardless Synthesizer 101, with a few exceptions. It was designed to sit upright, behind the 101. Instead of glide controls, the 102 has a sample-and-hold module with variable lag time, and instead of noise, the 102 has a ring modulator. The 102 also features weak and strong sync inputs and a mix cascade jack socket instead of the tuning oscillator.
This was a simple 4 X 2 mixer/amplifier, featuring panning, mono F/X send and return, VU meters, a built in reverb, as well as separate left and right speaker and line outputs. It was designed to sit to the right of the 101.
The 104 is a 12 X 2 step sequencer, featuring variable gate time, series or parallel configuration, switchable ranges, and buttons for Start, Continue, Stop, and Step. It was designed to sit to the left of the 101.
Actually a pair of 16cm 3.5W speakers in angled boxes, designed to sit at either side of the 102.
Roland had apparently intended to design more components for the System 100 but chose, instead, to put their efforts into designing the modular System 100m.
[from The A-Z of Analogue Synthesizers, by Peter Forrest, published by Susurreal Publishing, Devon, England, copyright 1994 Peter Forrest]