KORG 03R/W is a compacted version of 01/W. Its synthesis engine is called ai2 (advanced integrated square).
KORG 03R/W (1992)
Overview
03R/W is a simple PCM synthesizer with GM standard sounds. It has 5MB PCM ROM, which is essentially a replication of 01/W's 6MB Waveform sets. 32 polyphonic, 8(16)-part multi-timbre, 2 multi-effects. The filter has no resonance, as 01/W does. 01/W's Waveshaping is gone - it became a straightforward PCM synthesizer. The Emphasis function remained, as all ai2 synths do. It adds slight high-frequency stimulation to the waveforms.
Sound Examples
Here are some .mp3 examples of 03R/W. While all sound examples of 01/W on this site used Waveshaping, these sounds below shows the normal use of zero series without waveshaping.
See also Behringer Modulizer Pro DSP1224P page for effected examples of 03R/W.
KORG 01/W is the base model of the 03R/W. It has Waveshaping function for resonance emulation and various waveform distiorting effects.
03R/W's PCM engine sounds almost the same as 01/W, except that it has no waveshaping. It can be seen as a GM-compliant and simpler version of 01/W.
KORG 01/W (1991)
KORG AG-10 is the lowest model of ai2 synths. It has unique bug to generate various musical noises. I couldn't find such an interesting feature in 03R/W.
KORG AG-10 (1991)
KORG M3R is the lowest model of the previous generation, ai synths. It's a 2MB ROM version of KORG M1. 03R/W inherits M3R's concept.
03R/W also uses the same housing of KORG WAVESTATION SR, which is a compacted version of WAVESTATION. RE1 is a remote editor for some KORG products like M3R, 03R/W, Wavedrum, etc.
KORG reissued the ai2 synths by more concentrating on GM standard in later models like X series, 05R/W, and N series. They have more variety in sounds, but it's my impression that 01/W and 03R/W sounds more hi-fi than all later models.