In 1970, a company named Telemed built an Electrocardiograph analysis service where hospitals would call in from all around the country and send ECGs over the telephone line with analog FM signals, three channels at a time. The computer located near Chicago would accept the incoming call, digitize the three analog signals every 2ms to 10 bits, write them to disk, and decode the touch-tone patient ID.
When the call was completed, the data from disk would be assembled into a full ECG record and written to tape, and simultaneously passed to the diagnostic program written in Fortran. The system would then initiate a phone call to the hospital's printer and print out an English-language diagnostic. The result was then available in ten minutes to the staff a the hospital.
The front end and back end was all Sigma 5 (first SDS then Xerox midrange real-time computer) assembler in an interrupt-rich process--one interrupt every 2ms for the analog, one interrupt for the disk write complete, interrupts for the tape record writing, interrupts for the outgoing phone call progress. This included an cost optimization process that would choose which line (this was in the days of WATS lines) based on desired response time. The middle was the Fortran program that would analyze the waveforms, identifying all the ECG wave forms--P-wave, QRS, and T-Wave--the height, duration, sometimes slope.
This all took place in a machine with 32k words (four bytes per word). There were two computers, one nominally used for development, but could be hot-switched if the other failed. I think downtime was on the order of an hour per year. This would have been called an Expert System, but I don't think the term was in common use as yet.
So the answer to your question is: "A considerable amount". Today we are all spoiled by environments with more memory on one machine than existed in the entire world at that time.