PLATO and Me

Wow, that was a blast from the past!

Mike the Mad Biologist links to “an excellent article about the PLATO computing system”.

I didn’t know all the early history.  My own involvement with PLATO begain in the ’80s when I was an instructor at Control Data Institute in St. Louis.  The courses were basically all PLATO, although the students had some projects to complete as well:  on the tech. side, it was mostly building circuits; on the programming side, students had some programs to write.  The instructors were there mostly to assist with the projects.

We eventually replaced the stand-alone PLATO terminals with CDC-110s which had a CRT terminal with a built-in keyboard and a separate double-sided, double-density eight inch floppy.  In PLATO mode, a Z80 microprocessor in the terminal was the boss, and another Z80 in the floppy drive just did the disk I/O; but it could also run CP/M in which case the Z80 in the floppy drive was in charge and the Z80 in the terminal ran the CP/M BIOS.

They also had a text editor called MINCE which the programming students used to write their programs instead of punching cards.  One of the languages we taught was RPG II which required codes to be “punched” into particular columns, so I wrote an RPG mode for MINCE that expanded tabs to the appropriate columns.

MINCE was written in BDS C, an early (and incomplete) C compiler for CP/M systems; and it came with source listings for much of the editor.  I didn’t know C at the time, so I went to a bookstore to get a book on C; and as luck would have it, the book I selected was the first edition of K&R, so I got off on the right foot. ๐Ÿ˜Ž

My first home computer was a CDC-110 with a dual floppy drive and a modem that ran at the phenomenal speed of 1200 baud!  I got all that for half price (around $5k IIRC) because I was a Control Data employee, and I eventually sold it for about what I’d paid for it. ๐Ÿ˜Ž

CDC eventually got rid of all the land lines and rotary switches for communicating with the PLATO mainframe in Minneapolis and switched to something called the “shared network” that used satellites.  This had the unfortunate effect of increasing the turn-around time for each keystroke to a large enough fraction of a second for H. sapiens to notice.

To the tune of Alabama Bound (with apologies to Lead Belly):

I’m input/output bound.
I’m input/output bound.
If them bits don’t stop, Babe, and turn around,
I’m input/output bound.

Hey listen all you hackers,
Now don’tcha be like me:
You gotta stick with that old PLATO rotary
And let that shared net be.

I’m input/output bound.


  1. K says

    I remember CP/M; it was a great operating system for the time, then DOS took over.

    What a time to be alive; things have moved so fast in the past 60 years.

  2. billseymour says

    … things have moved so fast in the past 60 years.

    Has it really been that long?  Now I do feel old!

    I’ve punched more than a few Hollerith cards and sorted them using a sorting machine.  I even remember how to punch an 026 drum card.  I guess the good news is that wired boards were before my time. ๐Ÿ˜Ž

  3. K says

    Have you ever tripped and dumped a box of punch cards on the floor? I have. ๐Ÿ™‚ Glad we’ve come so far. ๐Ÿ™‚

  4. says

    Z80s. CP/M. Suddenly, I’m getting nervous all over. Sweat breaking out. 8085. Nausea starting. Wait… Wait… 68000. Flat address space. Breathing becoming steadier… Memory mapped I/O… Calming down… calming down…

    I have to be careful visiting here, Bill.

  5. says

    PS- I didn’t have to deal with boxes of cards, but I do remember coils and coils of 7 bit punched paper tape for PDP-11 terminals. Rolls of the beasts, affixed at the end with a small piece of masking tape so that they wouldn’t unroll and turn into a giant Mobius strip.

  6. billseymour says

    jimf:  ๐Ÿ˜Ž

    Yeah, the 68000 was Really Cool for its day.  I even bought a book about it and learned the assembly language; but I never got to use it for anything real.

    Before my PLATO days, I worked for a hospital in Pittsburgh where I designed and built an EKG machine with a microprocessor in it.  The CPU we used was a Texas Instruments TMS9900 (not my choice), which had 16-bit registers at least, but was kinda ugly in other ways.  In particular, it implemented its general purpose registers in memory and had a CPU register called the workspace pointer which contained the address of the current register 0.  This was supposed to allow really fast context switches; in practice, it made for really slow registers.

    When I went to post this comment, I saw that you had another comment of your own.  The first computer I ever wrote anything real for was a PDP-8 with an ASR 33 teletype for a terminal, and I still have some punched paper tape to prove it.

    “Those were the days.” ๐Ÿ˜Ž

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