You could say that E4 has been produced in three main series.
The first that was round produced include EIV and E64. These could be upgraded with 32 pin SIMM memories. However, 32MB 32 pin SIMM memory almost impossible to obtain.
Classic: The second series of the E4 product called “classic”. Those included in this is the E-synth, E6400 and E4XT and the E4k. This product line has 72 pin SIMM memory. E6400 was the one who replaced the E64 and, in common with E4k it had 64 voices and cold be upgraded to 128 voices and 128 MB sampling memory.
Ultra: Ultra was the last series of hardware samplers produced by E-mu. Ultra line was a big step forward for the E4 family. Ultra series had several good features such as importing WAV files from DOS formatted floppy disks and IDE hard drive support.
The EIV Main Spec:
Memory Size: up to 128MB
Analog Sample Rates: 22.05kHz, 24kHz, 44.1kHz, 48kHz
Digital Sample Rates: 32kHz, 44.1kHz, 48kHz
Sample Playback: 44.1kHz, 48kHz
Sample Bits: 16 bits input / 18 bits output
Number of Voices: 64 or 128
Playback Frequency Range: 20 – 20kHz +2/-1dB
Signal to Noise Ratio: 94dB
Pitch Shifting: +/- 5 octaves constant sample rate
THD + Noise: less than 0.02%
Stereo balanced analog sample
Stereo digital input on XLR (AES/EBU or SPDIF)
ASCII keyboard port (PC/AT), optional
1 x SCSI 50 pin Centronics interfaces, secondary SCSI optional
Eight individual analog balanced outputs (polyphonic),
configured as 6 subs, 2 main, all on stereo jacks
Stereo Digital Output on XLR (AES/EBU or SPDIF)
Output Level is +4dbm, max 12V peak to peak
MIDI IN, OUT and THRU