ADVENT #11 — cmx 600

Little to say about Alice for today’s catch-up installment. As I worked on the core dialect this morning, I was reminded that a Scheme (cons) cell is implemented just as a frame represented by an addr cell. (car) returns the zeroth element of a frame. (cdr) returns the first. Alice really doesn’t care what you put in the tape, so long as it knows how much tape. Want an Alice tape with analog frames? No problem.

Our removable media for this installment is the hybrid analog/digital removable disk packs for the CMX 600 non-linear video editing system. Our last installment was about the hybrid analog/digital laserdisc and its role in the early 80’s non-linear editing system EditDroid from George Lucas. The CMX 600 may be the very earliest non-linear editing system dating from 1971.

Though the computer behind the CMX-600 was a PDP-11 with 32k RAM (too bit for the 24 x 24 series, alas), it was a lot like the later EditDroid. Laserdisc started as an analog media and grew digital features, while the CMX disk packs started as digital minicomputer hard drives and were modified to record analog video signals straight to disk. This is not the stretch that it may seem. Even into the microcomputer era, hard drives used pretty simple and inefficient FM recording schemes. With the disk divided into tracks anyway, it’s easy to separate the analog from the digital arenas. Video quality wasn’t especially important for either EditDroid or CMX-600 — these editing workstations didn’t produce the final product in any case. They produced ‘edit decision lists’, a series of cuts (literal cuts in the case of film) that would be made to stitch together the original high-quality sources into a final work. I wonder if there is anything like that for debugging — low-fidelity execution record used to stitch together a final execution.