[TUHS] Compatibility question

Paul Winalski paul.winalski at gmail.com
Wed Dec 20 07:31:43 AEST 2023

On 12/19/23, Clem Cole <clemc at ccc.com> wrote:
> Tom smiled while reading that man page: "It is assumed that the TN print
> train is being used."
> I have to wonder how many younger programmers know what a print train is,

For the edification of those who don't know, the 1403 line printer and
its brothers worked like this.  There was a (removable and switchable)
horizontal cartridge that sat midway in the printer, laid out
horizontally across the paper, behind an ink-soaked cloth band located
between the print train and the paper.  Behind the paper was a series
of 132 hammers (one per column of print).  The cartridge contained a
single chain of type that was spun at high speed.  Whenever the
position of a desired character passed in front of its desired colu,
that column's hammer struck the back of the paper and thus printed the

There were several print trains available, just as there were several
typeballs for the IBM Selectric typewriter.  One of these used a space
character '  ' both for the space and for the underscore '_'.  This
was the origin of using underscores to represent spaces in program

The other way to do line printing is to have a rotating drum with the
full character set for each column.  This is the way the DEC line
printers worked.  Of course there were minor inaccuracies in the
timing of the hammers, and with the drum-based printers this resulted
in wavy lines.  There were inaccuracies in the print train-style
printers, too, but waviness in the columns is not as noticeable to the
eye as waviness in the lines.  Coming from the IBM world, I considered
the DEC printers total junk.

> Paul -- you left out the other "feature" -- the noise, which was still
> deafening even with a model N1 and its cover.

Yes, the 1403 was very loud.  The pitch of the noise varied with the
sequence of characters being printed.  Some IBM hacker (yes, they
existed) came up with a deck of cards that, when printed, played
"Anchors Aweigh" on the 1403.  IBM field service wasn't very keen on
this hack because it put a lot of wear-and-tear on the print train.

-Paul W.

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