E-mu Systems came to prominence in the early 1980s with its relatively affordable Emulator sampler, and subsequently pioneered sample-based synthesis technology with the Proteus range. Unlike earlier types of synthesisers, sample-based equipment does not derive its raw sounds from electronic oscillators or algorithmically generated waveforms, but from recorded sounds held in read-only memory (ROM) chips. These sounds may then be layered, filtered, modulated by low frequency oscillation and shaped by ADSR envelopes. However, unlike a true sampler, such devices do not allow the user to record sounds but instead offer a range of factory sounds suitable for any given use. This type of sound production dominated electronic music production for several years in the late 20th century. The exclusive license for re-formatting and managing historical E-MU Proteus sound content has been acquired by Digital Sound Factory.

The original Proteus series are basic ROMplers which contains 3 base models with 192 patches each, of which 64 are editable by the user. The patches have an assigned sample and allow basic ADSR editing, and it's possible to link more than one patch together for a richer sound. The units have 32 voice polyphony.

The Proteus 1 contains general sounds from the Emulator library useful for music production, the Proteus 2 specializes in orchestral sounds, and the third model in sounds for world music. Additional versions include the following:

• XR versions have 256 slots editable by the user but are otherwise identical to the base models.

• The Proteus 1 Plus Orchestral model is a Proteus 1 XR with the sounds of the Proteus 1 and 2. It contains the ROM presets for the Proteus 1 and some from the Proteus 2.

• The Proteus FX is essentially a cost-reduced extended Proteus 1 plus Orchestral with the addition of some built-in effects. It has 512 presets, of which 256 can be edited by the user. The power supply is an external brick, and the additional sound outputs/inputs of the earlier models, which could be used for external effects, are not present.

• Proteus MPS (Master Performance System), a 61-key keyboard version of the first Proteus module. A Proteus MPS plus Orchestral was also available with sounds of the first two modules.

• The Pro/cussion is a module dedicated to percussion sounds.

The second generation of E-MU ROMplers added a filter.

• The first module based on the new chip was the Vintage Keys, which had a low-pass filter.
• The Morpheus added a complex filter engine with 197 filter presets, but was no commercial success.
• The UltraProteus is an extended Morpheus with the sounds of the three Proteus modules and more filter presets.
• The Planet Phatt module has sounds for Hip-Hop, the Orbit 9090 for Techno/Electronica, and the Carnaval for Latin music.

The Proteus 2000 released in 1999 was a 1U rack sound module based on Audity 2000 released in 1998. It contained many "bread and butter" sounds,^[3] among just over a thousand waves utilising 32 megabytes of ROM. It featured up to 128 voice polyphony and 32-part multi-timbrality.^[4] It could be expanded with slots for three additional sound ROM cards. A cheaper Proteus 1000 model was also introduced with the same soundest and ROM but only 64 voice polyphony and fewer individual sound outputs. The Proteus 2000 also has Protozoa ROM expansions that contain patches from the original Proteus trilogy, where the first 128 patches towards each of the three modules respectively were faithfully re-mastered digitally from scratch that could be purchased to add onto the module, consisting a total of 384 patches of up to 16 MB of memory.

The Proteus 2000 range also consisted of several specialized models, some differing from each other only by the sound banks they contained. However, most allowed four ROM chips to be mounted, and these chips were available separately, so real differences might be simply cosmetic. The available ROM chips included the Composer, a work-horse set of sounds useful for popular music production, three orchestral ROMs, the Vintage Keys collection of electric organs, pianos and classic synthesisers, a chip dedicated to the Hammond organ and a drum ROM as well as the Orbit and Mo-Phatt collections, aimed at dance and urban genres and the Xtreme Lead, optimised for monophonic synthesiser soloing. Most of these were also sold as specialized modules, even though the hardware inside most of there is virtually identical to the Proteus 2000.

This 4U rack model was designed to function as a rack-mounted, front-panel-programmable sound source. It was equipped with sixteen multi-function pads and the same number of programmable knobs and had an onboard sequencer.

In 2001 the Proteus line of modules was repackaged in the form of a line of tabletop units, the XL7 and MP7 Command Stations, broadly similar to the rack-mounted 2500 in features but featuring touch-sensitive pads suitable for recording drum patterns.

In 2001–2002, E-mu/Ensoniq released a trio of entry-level keyboards, essentially the keyboard versions of the Proteus 2500 module. The E-mu MK-6, XK-6, PK-6 and Ensoniq Halo featured the same 61-key keyboard and controls layout, but slightly different soundset.

Prodatum^[5] is a cross-platform software editor for the Proteus 1000/2000, Command Stations and keyboard versions. prodatum is free software.

Proteum^[6] is a free Windows software editor for Proteus and Command Stations.

Since Creative withdrew their provision of historical OS updates and manuals for most of the older E-Mu gear sometime around August 2011,^[7] many of these files have been made available elsewhere, such as Synth Gear Docs Archive and the E-Mu Legacy Archive.

Mark Snow used the Whistl'n Joe instrument patch (Patch #125 on the Proteus 2) for The X-Files theme.^[8][9]

Eric Serra used the Infinite One instrument patch to get the sharp, metallic percussive sound that is featured in his soundtracks, such as in The Fifth Element, Leon the Professional, and GoldenEye.^[10] Subsequently, the video game composer Graeme Norgate^[11] would use the same patch in games such as GoldenEye 007 and Perfect Dark. The sound originally is from a tambourine, pitched down, and treated with delay and reverb effects.

Mike O'Donnell & Junior Campbell for seasons 3-7 of Thomas & Friends and Andrew McCrorie-Shand for the original series of Teletubbies.

• "Product History". E-MU Systems. Archived from the original on 2011-08-09.