CRT displays [was: computer graphics in the 1950s]

Christian Corti cc at
Sat Oct 18 04:07:35 CDT 2008

On Fri, 17 Oct 2008, Tony Duell wrote:
> Actually, I believe there was a CRT-like device (I forget the name --
> 'Charactertron'?) where you did sort-of send the characters to the CRT.
> THe CRT had 3 deflection systems and an electode between them that
> cotnained the patterns for all the xymbols (characters, etc) that the
> device could display. You used the rearmost deflection system to direct
> the beam from the electron gun at the right pattern and the front
> deflection system to put it at the right place on the screen. No, I don;t
> have one.

This reminds me of the CRT display of a Cogar C4 (or ICL/Friden 1501). It 
is a standard 5" CRT with an almost ordinary deflection system. But the 
deflection itself is rotated/mirrored, i.e. the "vertical" sweep is from 
left to right and the "horizontal sweep" from top to bottom. So the 
display controller writes all characters from the first text column first 
(and then IIRC only the text lines 1,3,5 and 7). Then comes the next 
columns. After all 32 columns come the even text lines (there's a display 
mode which only displays lines 1,2,3 and 4; the display has a 32 x 8 
character cells). But that's not all. There is a second horizontal 
deflection coil that interferes with the first main deflection coil (I 
think this is called twiggle sweep or something like that). This second 
coil deflects the beam according to the width of one character cell, and 
one raster line of a character is written on the screen during this time.


More information about the cctalk mailing list