The Sony PCM-F10, though not the first digital stereo recorder, was the first to make it truly affordable.
PCM is the acronym for Pulse Code Modulation, which is the recording technique for recording digital data on tape. To achieve a low cost, the PCM encoder/decoder used a standard Betamax Video deck, though any video deck would usually work.
The initial system was somewhat bulky and by 1981, Sony released the second generation called the PCM-F1 which reduced the processor size substantially. Quality (although not up to current standards) was actually quite respectable. The analog to Digital and Digital to analog (ADC and DAC) chips developed for the F1, soon found their way into the very first CD players.
Considering Sony's $2500 PCM system was only about 1/10th the cost of a dedicated digital recorder at the time, the F10 & F1 became milestones in the start of the digital audio revolution.
The technology incorporated into the PCM-F1, paved the way for the soon to come DAT machines.