Comment by retrac

Bandwidth and storage.

The Viking landers (1975) were very sophisticated with robotic arms and mass spectrometers, adorable little anemometers, digital colour cameras, the whole deal, with 5 megabytes of digital tape storage.

The downlink rate was 16 kbps when related by the matched orbiter; otherwise direct communication was at 250 bps.

The digital cameras were pushing the absolute limit of technology at the time. The digitizer produced a 16 kbps bitstream that fed the uncompressed image directly to the transmitter taking four minutes to send an image. It could also be stored on tape for later transmission, but it used much of the tape to do so.

If it had included a microphone and ADC, it would have been technically possible to record a few minutes of audio and then spend hours transferring it back to Earth. But the kind of constant monitoring now done really depends on the more than 1 Mbit/s of bandwidth now available thanks to half a dozen Martian orbiters, and all the fancy processors and gigabytes of storage the landers and rovers now have.