Timesharing on the MIT Weather Radar PDP-8/IX

Histories
, , ,
102

Fredkin was my undergraduate advisor in Computer Science. I’ll speak more about him in future postings.

1 Like
103

“Party on the fantail” reminds me of this excellent legend, with which bill75 is familiar.

104

Speaking of his excellent coding style, bill75 taught me a lot, but the two most important lessons in programming were invaluable to me in every subsequent job:

  1. An ideal subroutine does exactly one thing and returns. Ditto for functions, methods, messages or whatever your language calls them.
  2. The structure, function and necessity of a clock queue. Many times I’ve helped colleagues out of a hole they’ve dug for themselves trying to manage more than one timing-related event in a single program. The clock queue is self-evidently the solution, once you know about it.
1 Like
105

As promised, Weather Radar on a PDP-8 in Antarctica is my followon to this thread.

1 Like
106

Would you mind explaining what a clock queue is?

107

In essence, a clock queue is identical to the keyboard ring buffer explained by Bill above. Program(s) that need a task done at a specific time put a [timestamp, link-to-task] on the queue, sorted in timestamp order. Clock ticks examine the head of the queue, and if a timestamp has passed, remove the item and wake up the corresponding task. Then loop back to see if there are other timestamps that need to be serviced.

1 Like
108

Thanks.

That kind of service is very common in emulators, where various hardware devices usually need to schedule future actions.