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Some early computers had vector displays, which allowed the computer to draw graphics by steering a cathode-ray beam. Some examples include the Whirlwind, TX-0, TX-2, and PDP-1.

It would be easy for a computer manufacturer to re-brand a commercially-available oscilloscope as the display device, or expect the end-user to supply their own oscilloscope. Did any computers instead use a display that was custom designed and built for the computer?

Real computers please, not arcade games (no Asteroids, Tempest, etc.).

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  • There's a lot of stuff in an oscilloscope a computer display doesn't actually need. A computer manufacturer who wanted to "mass-"produce (mass is relative here) at cost would probably not use a device that by far exceeds the accuracy and versatility they need. Most of the early graphic displays were actually derived from radar equipment.
    – tofro
    Apr 1, 2021 at 11:16
  • The PDP-1 display was a point-plot display; I think the program could just say "light the dot at position [X,Y]", and as far as I recall, had to keep doing it (i.e., was likely following a display list). That doesn't sound very oscilloscopy to me.
    – another-dave
    Apr 1, 2021 at 12:08
  • @tofro: Sure, there would be a cost involved to include a full scope, but a fraction of the cost of the computer. Some users might already have a scope and no need to get another. It could also be useful beyond the computer. Similar to cassette recorders for early micros: some had them built in, others required the user to provide them.
    – DrSheldon
    Apr 1, 2021 at 12:24
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    @another-dave: You would put the scope into X-Y mode. There's no reason to use the time-sweeping or trigger circuits.
    – DrSheldon
    Apr 1, 2021 at 12:25
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    @DrSheldon - all those things that were easy to do on classic oscilloscopes that are really hard on a modern digital scope. I keep looking for the Z input on the back and just can't find it...
    – Jon Custer
    Apr 1, 2021 at 13:14

3 Answers 3

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The PDP-1 Type 30 display, which is the 'canonical' display for the PDP-1, was a point-plotting display, not a vector display. It was a specific device, not a general-purpose oscilloscope.

Link to manual. The price list gives it at $14,300 in 1964, though that's the Type 30, not the 30E.

HOWEVER, this 1964 PDP-1 price list lists

OSCILLOSCOPE DISPLAY
TYPE 34

Plots data point by point on an X-Y plotting scope such as the Tektronix Model RM
503. Ten bits per axis.
                                                         Control only                  $  3,060
                                                         With oscilloscope             $  3,900

So the answer to your question is 'both'. The PDP-1 could support a dedicated display device or an off-the-shelf oscilloscope as a display.

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    @DrSheldon (your edit). I'm a programmer. 'or' obviously includes the possibility of 'both' :-)
    – another-dave
    Apr 1, 2021 at 13:35
  • Fair enough. Anyways, best answer to the question, gets the checkmark.
    – DrSheldon
    Apr 1, 2021 at 13:46
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Well, I give you the SYM-1, as it could display text output on a user-supplied oscilloscope. Ray was just too much of an engineer to let that pass :) (*1)

Beside that somewhat off beat example, I'd say next to every analogue computer would work great with a user supplied oscar.

In a more general notion, at a time when displays became a thing, a user supplied oscilloscope as default device wouldn't make much sense, as it would increase the system price a lot, as it, for one, would include many expensive components not needed for the task, while the computer side would still have to include everything necessary to generate a picture.

The CDC displays are a special case, as here the display 'only' needed a pair of DA converters, while the already existing peripheral processors would provide the data stream. But even here it was more appropriate to supply the screen as part of the console needed anyway for interface and keyboard.

*1 - Using XY output was kind of popular in the 70s for folks with good tools - and due the same reason (an oscilloscope was expensive) not really seen outside of well fitted shops, which was the majority of hobbyists. I still have, somewhere, a board I made at that time to read out a PROM as hex on an oscilloscope. one line of 4 bytes at a time, a button to reset address to zero, one for up one for down. Hardware was just a set of counters to address and 'micro step' plus resistors as DAC.

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    One day I'll set my SYM-1 up to drive an oscilloscope, but I suspect I need more RAM
    – scruss
    Apr 1, 2021 at 17:50
  • @scruss Why mire RAM? IIRC it works with the basic unit. No Expansion needed. Also, didn't the SYM come with sockets for a humongous 4KiB of RAM - not to mention the ability to use one of the ROM sockets? I belive even the SYM-BASI (in ROM) would run well with 4 KiB.
    – Raffzahn
    Apr 1, 2021 at 18:15
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The PDP-1 actually used a CRT that was designed for radar (see e.g. the Wikipedia entry).

But the whole electronics around the CRT needed to drive the CRT and interface it with the PDP-1 was custom built. And as such, it was nothing like the electronics needed in an oscilloscope.

The same is true for later displays used in the PDP series.

So the assumption

It would be easy for a computer manufacturer to re-brand a commercially-available oscilloscope as the display device, or expect the end-user to supply their own oscilloscope

is not how it was done initially on the PDP-1.

Looking at the various handbooks on Bitsaver, we see the follow progression:

  • April 1960: Mentions "the PDP-1 CRT display" and "lightpen" on p. 23. No model numbers.
  • 1961: "Visual CRT Display (Type 30)", "Precision CRT Display (Type 31)", "Lightpen (Type 32)" on p 27.
  • June 1963: same (p. 32)
  • Oct 1963: same (p. 33), additionally with a "Symbol Generator (Type 33)", but with an "Oscilloscope Display (Type 34)" on p. 6, without details later on.
  • June 1964 pricelist Oscilloscope Display Type 34, e.g. for Tektronix Model RM 503.

So one can see that the variant for an off-the-shelf oscilloscope is clearly an afterthought, and the question is still if anybody used that (though it was a lot cheaper, which is also very interesting). So I wonder how the quality and screen size of that scope compared?

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  • I just found a mention of a 'type 34' display using a scope.
    – another-dave
    Apr 1, 2021 at 12:56
  • @another-dave Interestinly enough, in the PDP-1 handbook the type 34 is listed at the beginning, but not explained at all in detail later on (while the type 30 and 31 are, with pictures). So I suppose while it's technical possible to separate the type 30 or 31 controller from the CRT and sell it as a stand-alone device, without a CRT, and hook it up to an off-the-shelf oscilloscope, if this was actually regularly done by people I'd expect more information about that in the handbook...
    – dirkt
    Apr 1, 2021 at 13:52
  • I never heard of it before, I just blundered into it in the price list. Who knows if DEC actually sold any?
    – another-dave
    Apr 1, 2021 at 14:41
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    Oscilloscopes have CRTs that are optimized for extreme speed and sensitivity, not big display sizes or high resolution.... there is the need to display something like a 10nS/div sweep on some designs (effectively having 10 million FPS :) ). This means you need electrostatic deflection at a sensitivity you can still build a viable wideband amplifier for. So you have a choice of using a TWO FEET long CRT with just a 5" round screen (to keep the deflection angles low), like in a Tektronix 545/547, or use expansion mesh techniques that limit resolution, like in a Tektronix 7603.
    – rackandboneman
    Apr 3, 2021 at 18:29

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