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Hacking With Telex |
When CDC added timeshare to the punch-card batch-job designed Cyber machines, |
they made two types of access to the system: Batch and Telex. Batch is a |
punch-card deck, typically, and is run whenever the operator feels like it. |
Inside the system, it is given ultra low priority and is squeezed in whenever. |
It's a "batch" of things to do, with a start and end. |
Telex is another matter. It's the timeshare system, and supports up to, oh, |
60 terminals. Depends on the system; the more RAM, the more swapping area (if |
you're lucky enough to have that), the more terminals can be supported before |
the whole system becomes slug-like. |
Telex is handled as a weird "batch" file where the system doesn't know how |
much it'll have to do, or where it'll end, but executes commands as you type |
them in. A real kludge. |
Because the people running on a CRT expect some sort of response, they're |
given higher priority. This leads to "Telex thrashing" on heavily loaded CDC |
systems; only the Telex users get anywhere, and they sit and fight over the |
machine's resources. |
The poor dorks with the punch card decks never get into the machine, because |
all the Telex users are getting the priority and the CPU. (So DON'T use punch |
cards.) |
Another good tip: if you are REQUIRED to use punch cards, then go type in |
your program on a CRT, and drop it to the automatic punch. Sure saves trying |
to correct those typos on cards.. |
When you're running under Telex, you're part of one of several "jobs" inside |
the system. Generally there's "TELEX," something to run the line printer, |
something to run the card reader, the mag tape drivers (named "MAGNET") and |
maybe a few others floating around. There's limited space inside a Cyber.. |
would you believe 128K 60-bit words?.. so there's a limited number of jobs |
that can fit. CDC put all their effort into "job scheduling" to make the best |
of what they had. |
You can issue a status command to see all jobs running; it's educational. |
Anyway, the CDC machines were originally designed to run card jobs with lots |
of magtape access. You know, like IRS stuff. So they never thought a job |
could "interrupt," like pressing BREAK on a CRT, because card jobs can't. |
This gives great possibilities. |
Like: |
Grabbing a Copy Of The System |
For instance. Go into BATCH mode from Telex, and do a Fortran compile. |
While in that, press BREAK. You'll get a "Continue?" verification prompt. |
Say no, you'd like to stop. |
Now go list your local files. Whups, there's a new BIG one there. In fact, |
it's a copy of the ENTIRE system you're running on -- PPU code, CPU code, ALL |
compilers, the whole shebang! Go examine this local file; you'll see the |
whole bloody works there, mate, ready to play with. |
Of course, you're set up to drop this to tape or disk at your leisure, right? |
This works because the people at CDC never thought that a Fortran compile |
could be interrupted, because they always thought it would be running off |
cards. So they left the System local to the job until the compile was done. |
Interrupt the compile, it stays local. |
Warning: When you do ANYTHING a copy of your current batch process shows up |
on the operator console. Typically the operators are reading Penthouse and |
don't care, and anyway the display flickers by so fast it's hard to see. But |
if you copy the whole system, it takes awhile, and they get a blow-by-blow |
description of what's being copied. ("Hey, why is this %^&$^ on terminal 29 |
copying the PPU code?") I got nailed once this way; I played dumb and they let |
me go. ("I thought it was a data file from my program"). |
Staying "Rolled In" |
When the people at CDC designed the job scheduler, they made several "queues." |
"Queues" are lines. |
There's: |
1. Input Queue. Your job hasn't even gotten in yet. It is standing outside, |
on disk, waiting. |
2. Executing Queue. Your job is currently memory resident and is being |
executed, although other jobs currently in memory are |
competing for the machine as well. At least you're in |
memory. |
3. Timed/Event Rollout Queue: Your job is waiting for something, usually a |
magtape. Can also be waiting for a given time. Yes, this |
means you can put a delayed effect job into the system. Ha, |
ha. You are on disk at this point. |
4. Rollout Queue: Your job is waiting its turn to execute. You're out on |
disk right now doing nothing. |
Anyway, let's say you've got a big Pascal compile. First, ALWAYS RUN FROM |
TELEX (means, off a CRT). Never use cards. If you use cards you're |
automatically going to be low man on the priority schedule, because the CPU |
doesn't *have* to get back to you soon. Who of us has time to waste? |
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