first systems used for mastering audio compact discs in the early 1980s by many major record labels, with the final U-matic 1600-format digital audio tapes being sent to CD pressing plants to be recorded to a glass master disc used for making the replicated CDs. Several semi-professional/consumer models of PCM adaptor were also released by Sony: Sony PCM-1 (the first consumer-marketed model, introduced in 1977) Sony PCM-F1 (which was sold with a companion Betamax-format VCR, the Sony SL-2000, SL-F1, or SL-F1E, for recording & playback) Sony PCM-100 Sony PCM-501ES Sony PCM-601 (included SPDIF digital audio input and output) Sony PCM-701 Technics also made a battery-powered portable PCM adaptor, the SV-100, a hi-fi component adapter, the SV-110, and a version with a built-in VHS videocassette transport, the SV-P100. All the Technics (Panasonic) PCM adapters are limited to 14-bit resolution. Other makes and models of PCM adaptors offered on the market were the Nakamichi DMP-100, the Sharp RX-3, the Sansui PC-X1 and the Hitachi PCM-V300. dbx, Inc. also manufactured a pseudo-video adaptor, the Model 700. It differed from the above-listed models in the fact that it did not use PCM, but rather delta-sigma modulation. This resulted in a higher quality digital recording with more dynamic range than what standard PCM modulation could offer. Like a standard PCM adaptor, the Model 700 also utilized a VCR for a transport. Obsolescence In 1987, a few years after the PCM adaptor's introduction, Sony introduced a new cassette-based format for digital audio recording called Digital Audio Tape (DAT). Since DAT did not rely on a separate video cassette recorder, it was a much more portable and less-cumbersome format to use than a PCM adaptor-based system. DAT recorders had their own built-in transport using a small cassette unique to the format. DAT used tape in width loaded into a cassette 73 mm × 54 mm × 10.5 mm (2.87 in. x 2.12 in. x 0.41 in.) in size. The audio data was recorded to the tape by using helical scan recording, the same fashion that a VCR connected to a PCM adaptor would record to a videotape. In essence, DAT was a modernized, integrated, and miniaturized version of a PCM adaptor-based system. Like a PCM adaptor, DAT could record only two tracks of audio at a time, but the smaller size of the equipment and media, as well as being able to accept multiple sampling rates and