Experimental Ethernet, XGP, etc.

Josh Dersch derschjo at gmail.com
Tue Jan 23 13:24:55 CST 2018

On Tue, Jan 23, 2018 at 10:35 AM, Mark Kahrs via cctech <
cctech at classiccmp.org> wrote:

> A few notes:
> The experimental Ethernet speed was in fact 2.94 MHz: It's the Alto clock
> divided by 2.
> The Alto based printer was called "SLOT" -- Scanning Laser Output
> Terminal.  It was plugged into the Alto backplane and presented itself as a
> hardware peripheral controlled by microcode (as was the case for all Alto
> I/O).  It was an Alto task, of course.

There was also the later Orbit controller, which talked to a number of ROS
(Raster Output Scanner) devices, including the Dover.  The Orbit controlled
the ROS and the printer and had special hardware + microcode to assist in
the generation of raster bands (16x4096 pixels) for imaging.  This allowed
the Alto to keep up with the Dover (which was approximately 1 page/second)
in real time while generating 384dpi output.

(Incidentally, not all Alto I/O was implemented as hardware + microcode --
just the high-bandwidth stuff; there was memory-mapped hardware at the top
of the address space for keyboard/keyset/mouse and various other devices.)

Also: The latest version of ContrAlto (
https://github.com/livingcomputermuseum/ContrAlto) emulates the Orbit and
Dover ROS in case anyone's itching to print some PRESS files :).  Bitsavers
has a set of disks I put together with Spruce (one of a number of
Alto-based print servers) if you want to play around with it.

- Josh

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