by Darius Kazemi, July 9 2019

In 2019 I'm reading one RFC a day in chronological order starting from the very first one. More on this project here. There is a table of contents for all my RFC posts.

Even more graphics description

RFC-190 is titled “DEC PDP-10-IMLAC Communication System”, authored by L Peter Deutsch of Xerox PARC and dated July 13, 1971.

The technical content

This RFC describes how a DEC PDP-10 is connected to a remote IMLAC PDS-1 vector display. It's a display system that operates in a few modes: it can support the display of text strings at any position on the screen, it can simuate a teletype by doing line feeds and carriage return type layout (like a terminal screen), and it can move back and forth between these modes.

The system uses a mouse for control. The computer mouse is still pretty rare at this point (light pens and tablets are more common at ARPANET host sites) but if anyone is going to have a mouse, it's Xerox PARC, as they were a relatively early and enthusiastic adopter of the device. (Their Xerox Alto would go on to be the first personal computer designed around mouse input.)

The various system calls are documented in a really interesting prosaic format. For instance:

If first byte pointer is zero then

   if a new string is being written then

      an error code illstr is returned.

   Otherwise, the string already exists so

      delete the string from the display area.

If the first byte pointer is -1 then

   if a new string is being written then

      an error code illstr is returned.

   Otherwise, use the old string.

If the first character of the string is a zero character,
the string to be displayed is null, but the string is not

I love that each system call not only has its basic functionality described, but use cases and notes for each system call are also listed.

The system calls are somewhat similar to previous graphical display languages we've seen, wherein display areas are defined, cursors are positioned, etc.

Further reading

L Peter Deutsch had a long programming career and among other things is the primary author of GhostScript, but is now primarily a composer. He's interviewed in the popular book Coders at Work by Peter Seibel.

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About me

I'm Darius Kazemi. I'm an independent technologist and artist. I do a lot of work on the decentralized web with ActivityPub, including a Node.js reference implementation, an RSS-to-ActivityPub converter, and a fork of Mastodon, called Hometown. You can support my work via my Patreon.