Vintage Synth say :
The Proteus 1 is an economical one-space module consisting of your basic rock and pop sounds. It has 4 MB of sounds from the EIII library such as samples of pianos, organs, strings, horns, guitars, basses, drums, Latin percussion, and more all at your fingertips.
In 1990, the Proteus 2 was released which is identical to the Proteus 1 in most every way except that it has 4 MB of purely orchestral sounds - the same sounds from the Plus Orchestral ROM card, which also happen to come from the EIII library. This was the first time really high quality sounding orchestral sounds could be had in a dedicated sound module.