Because of the way the MT-32 offered custom instrument programming it was the only synthesizer that MIDI files written for it could be played on. And because it was so expensive not everybody could afford it. This contributed to the creation of the General MIDI standard in 1991. General MIDI was a set MIDI format with a list of 128 unchangeable instruments over 16 channels (the MT-32 only had 9 channels) so that, unlike the MT-32's ability to program custom instruments, MIDI files would all have the same list of instruments so that no matter what hardware you used to play them back it would sound the same on all of them (more or less).

In the same year Roland built on the GM standard with the release of the first Sound Canvas (the SC-55) and created GS (General Standard or General Sound). GS expanded the original 128-instrument GM standard via variation banks to over 300 instruments (as well as support for the default MT-32 standard, though without its re-programmability) and added a few proprietery MIDI controllers like Reverb and Chorus both of which could be triggered via MIDI data.

From that point on games with MIDI soundtracks almost universally supported the Sound Canvas as the best way to experience them. So much so that Roland created a software wavetable MIDI synthesizer based on the SC-55 for Windows XP called "Microsoft GS Wavetable", though the quality is no where near as good as a real SC-55 and it's missing some MIDI controllers like reverb and chorus among others.

At some point, someone figured out that this low cost (relatively speaking) unit was a good match up for computer games of the era and heavy marketing campaigns ensued. The MT-32 became the standard for computer game music for the next few years.

Game sound designers made good use of the machine and took the MT-32 to it's limits. Some even went beyond sound entirely and used MIDI SysEx commands to display messages on the MT-32's LCD screen.

CM-32L
Once the market for computer game sound hardware took off, Roland started to make synth modules that were designed specifically for the computer gaming market. The first such of these modules was the CM-32L (the “CM” stood for “Computer Music”, the “L” stood for Linear Arithmetic Synthesis, also known as “LA”).

Internally, the CM-32L contains everything that the MT-32 does, but contained an additional 33 samples in it's wave banks. Most of the added samples were sound effects. There are several games that make use of these added sound effects, such as Beneath a Steel Sky and Ultima Underworld. If you play these games with an MT-32, you will get the music, but you will miss out on a few sound effects here and there. This was designed in such a way that an MT-32 user would not know that they were missing anything but the CM-32L, CM-64, CM-500 user would be treated to a nice surprise with extra sounds.

Since the CM-32L was meant primarily for computer games, it lacked the buttons and LCD screen of the MT-32. The CM-32L only a single knob for volume, and two LEDs to indicate power and MIDI message status.

The sound output of the CM-32L was also a bit less noisy than that of the MT-32.

CM-64
At one point in time the CM-64 was the ultimate Roland game synth to own, but at a debut price of well over $1000 USD not many could afford it. The CM-64 is a CM-32L and a CM-32P combined into one box. It is fully MT-32 compatible. This unit will work just fine for MT-32 or CM-32L games, but few if any games were actually designed to utilize the CM-32P side at the same time as the CM-32L. The CM-64 has the same Roland PCM wave card slot on its front panel as the CM-32P.

LAPC-I
The LAPC-I (Liner Arithmetic Personal Computer I) was an ISA card that housed an MPU-401 MIDI interface along with a built-in CM-32L. This unit is fully compatible with both the MT-32 and the CM-32L. Basically, it's a CM-32L on an ISA card.

SC-55
The Roland SC-55 is a GS MIDI sound module released in 1991 by Roland. The SC-55 was the first sound module to incorporate the new General MIDI standard. It was the first in the Roland Sound Canvas series.

The SC-55 used both PCM and a cut-down version of the LA synthesis engine, to support 24-voice polyphony with 16-part multitimbrality. It came preloaded with the Roland MT-32's variation bank, but lacked the MT-32's re-programmability. Aimed at PC music enthusiasts, the SC-55 featured 317 instrument patches, including the GS drum kits and additional controllers. The selection of effects includes reverb and chorus.

SC-55 MKII
A minor upgrade to the original SC-55, the Roland SC-55mkII has increased polyphony (28 voices), more patches, raising the total number to 354 instruments and extended, and improved audio-circuitry in the form of 18-bit audio (versus 16-bit in the original SC 55). The SC-55mkII added a serial port as an alternative interface to the MPU-401.

SC-88
The SC-88 a 32 part multitimbral sound module with 64 voices of polyphony. It has 654 high-quality sounds, along with 24 types of drum sound sets. Amongst these sounds are the same ones as the SC-55/55MKII, which means that the SC-88 can correctly play the song data of these modules too.

The SC-88 was basically an expanded version of the SC-55MKII which was released in 1993. The SC-88 featured more memory, multitimbral, and polyphony compared to the SC-55MKII while also adding EQ.

SC-88 Pro
Roland released an upgraded version of the SC-88, called the SC-88 Pro in 1996, which improved on the original hardware with more drumsets, more tones, as well as the introduction of Insertion EFX and unofficial XG compatibility.

Yamaha XG (EXtended General MIDI) is an extension to the General MIDI standard, created by Yamaha. It is similar in purpose to the Roland GS standard.