CDC 6600 - Why so awesome?

Paul Koning paulkoning at
Fri Jun 24 10:01:28 CDT 2016

> On Jun 23, 2016, at 11:28 PM, James Vess <theevilapplepie at> wrote:
> Hey guys,
> I was looking and found that the Tektronix 4010 is a calligraphic display,
> for which I found a video!
> Let me know if it bares a resemblance to the display on the 6600

None, unless you count the fact that both are green and both use electrons.

The Tek 401x series displays are terminals (connected by a serial port).  They use storage CRT technology to create a persistent image (no refresh).  They do dot matrix ASCII text, line drawing, and have a crosshair cursor for input.  They use ASCII based text communication, at 9600 baud (I think they go that high).  The 4010 is rather a small tube, 24x80 characters; some other models are much larger and can do quite impressive graphics at fairly moderate cost by the standards of the time (mid 1970s).

The CDC 6000 series console (Data Display Co. DD60) showed up about 10 years earlier.  It's essentially a dual oscilloscope with X/Y input -- like typical oscilloscopes it uses electrostatic deflection.  The display itself accepts 9 bit X and Y coordinates, plus analog X/Y offset signals that are used to produce the character outlines, a size selection signal (small/medium/large) and a left or right intensify signal.  The X/Y deflection signals are applied to both tubes, but the intensify signal controls which of the two lights up.  In theory you could light up both simultaneously; the CDC controllers would not do that.  There's also a keyboard, with a 6 bit data signal plus key up/down signals.

The 6612 or 6602 controller ("synchronizer" in 6000 terminology) connects a 6000 I/O channel to the DD60 (or, for some models, to a pair of DD60s).  It interprets commands to produce the X/Y position signals, advances X after each character, and converts character data into the X/Y offset waveforms.  The waveform generator is essentially a counter feeding a ROM which feeds a set of D/A converters.  In the 170 series, it was done that way, but in the 6000 series display controller, the waveform generation uses a large complex collection of gates instead of a ROM.  Why, I'm not sure.  A possible answer is that a sufficiently fast ROM (100 ns lookup time) wasn't available in the early 1960s.  The controller, when in keyboard input mode, would read the keyboard lines and deliver the data (or 0 meaning no key down) to the PPU.  No rollover, which meant that typing fast required some practice.

Since the DD60/6612 hardware had no refresh machinery at all, the driving software would do the refreshing.  This made the display very dynamic.  By contrast, a Tex 401x is a storage tube, which puts it at the other extreme: once you draw a character or line, it would stay without any further action.  You can't erase it; the only erase available is a full screen erase.


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