CDC 6600 display character generation

[Eric Smith]

On Wed, Jun 6, 2018 at 9:20 AM, Toby Thain via cctalk <cctalk at classiccmp.org
> wrote:

> On 2018-06-06 9:48 AM, Noel Chiappa via cctalk wrote:
> > (BTW, the VT11 in DEC's GT40 used bit maps for its built-in character
> geneator,
> > and the hardware did tiny raster zones to display them!)
>
> As does the PDP-1 (point plotting, 5x7 I think).
>

Some variants of the Type 30 display, used on the PDP-1 and other early DEC
computers, included a Type 33 character generator option, which works as
you describe. The computer sends two 18-bit words, which are interpreted as
a 5x7 bitmap, with the leftover bit used to shift the character slightly
for a subscript.

The Type 30G display has the Type 33 character generator as a standard
feature. The PDP-1 at the Computer History Museum has a 30G, but the
character generator is not completely working.  I suspect that most PDP-1
installations did not have the character generator.  There is not known to
be any surviving PDP-1 software that used the character generator; I wrote
simple test programs we used to attempt to debug the hardware.