What is (was!) a PDP-8/L computer anyway?


Today we take personal computers for granted - they're getting almost as common as color televisions. When the Class of 1971 graduated from Wilton High School, things were just a wee bit different! There were still many black-and-white TV's around, and if your color TV had a remote control, it used ultrasonic sound to change the channel and adjust the volume (if you were lucky!).

Of course, CD-ROM's didn't exist (do your kids know what it means to sound "like a broken record"?), and we used slide rules to do math calculations (I really wish I hadn't thrown my precision Pickett 6-inch one away - it would make a great coffee table conversation starter...). We dialed the telephone, wound our watches (my kids can't read a clock with hands), and the cashiers at grocery stores actually knew the price of many common items because there were no barcodes! Almost every car had a carburetor (fuel injection, what's that?), many didn't have seat belts, and the Datsun 240Z had just come on the market at the "high" price of $4000 (my new 1970 Volvo sedan cost $2850)!

Those of you who are too young to have been around back then as well as those who were, but didn't take an interest in computers may find the following trivia of interest. These are my own recollections, which may not be accurate!

Along about 1968, Wilton High was the lucky recipient of a Digital Equipment Corporation PDP-8/L digital computer. I believe we were one of only four schools in the state to have a computer at that time. The computer was strictly for academic use - I don't recall that the school administration itself had a computer (classmates, help me out here!). My memory is that the complete system cost something like $20-$25,000.

The hardware (installed in a 6-foot high 19-inch wide rack mount cabinet) was an 12-bit processor, with 4 kilobytes of magnetic core memory that had a cycle time of something like 1.6 microseconds, which yielded a processor clock speed of about 700 kilohertz! The computer was assembled with discrete transistors (what's an integrated circuit, anyway?) which were interconnected by wire-wrapped circuits. A model ASR-33 teletype was connected to the PDP by a 110 baud current loop interface, and it sported a "hunt and punch" keyboard, a roll-paper printer (did we have paper towels in those days?), and a 10-character per second paper tape punch/reader for offline storage. It also had a high speed paper tape reader (300 cps?).

To boot the computer, you manually entered about 20 instructions on the front panel switches and then loaded the operating system/language interpreter from fan-folded paper tape. The Basic-like interpreted language was called Focal, and some of our most advanced programs would produce X/Y graphs (always with a relatively short Y axis and a much longer X axis!) or run overnight to generate prime numbers.

As I recall, the PDP was strictly for use by seniors. However, I was "close" to certain people in the math and science departments, and so I gained access to the PDP shortly after it arrived, when I was in 8th grade. By the time I graduated, I thought I didn't want to see a computer again! Somehow, somewhere, sometime when I least expected it - I got sucked back in to them! For the past 20 years, it's how I've made my living.

I'm composing this text now on a portable 300 megahertz computer with 128 megabytes of memory and 14 gigabytes of disk storage, not to mention the 56 kilobaud modem, the 1024x768 24-bit color display, etc., etc! What's next?

Here are some offsite links if you're curious: 


What is a PDP-8/L? (text only page)


ASR-33 Teletype (text with a link to a photo)



As I wrote the preceding words, I was struck with how crude so many technologies were in our high school days as compared to the present time. This, in turn, lead me to that "I'm getting old" feeling most of us get from time-to-time! However, a couple of days later I was struck by another thought - that at the same time we were "suffering" with all of this now-inferior technology, we were also putting men on the moon and bringing them back, several times, even with unexpected catastrophic failures (Apollo 13, which combined many things including now-dated but effective and well-crafted technologies, massive teamwork, the wherewithal of three brave and well-trained astronauts, and of course, some luck...).

In the present, I have a terrible time getting my own kids to do homework problems with English-to-metric conversions, for example. At the same time, we send the Mars Planet Orbiter on a journey to the red planet and it crashes for lack of such simple tasks! Perhaps things weren't so crude 30 years ago...

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Last updated:
January 26, 2012

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