17 Feb
2025
17 Feb
'25
12:52 p.m.
On Feb 17, 2025, at 2:58 PM, Van Snyder
<van.snyder(a)sbcglobal.net> wrote:
On Mon, 2025-02-17 at 08:53 -0500, Paul Koning wrote:
One of my university classmates worked for American Geophysical. They would lay out a few
thousand feet of cables with "geophones" on them, then drive around with
"thumper" trucks. They analyzed the data using Varian V70 computers with FFT in
microcode. They printed the resulting maps on 36" wide scrolls using — you guessed it
— Varian electrostatic printers.
...
The Varian brothers were true geniuses.
Indeed. There's a wonderful photo of them by Ansel Adams. Look for it; it shows the
two of them doing a mad-genius imitation, with a random collection of waveguides and the
like in their hands.
The Varian printer had one interesting issue. It had a chain drive, with some slack in
the chain. If you fed it data non-stop it worked great, but if you ever had to pause the
data stream, the stop and start of the paper would leave a gap in the output. Very
visible if you were trying to plot continuous lines (like the 5 horizontal lines in a
music score). The original application to feed that printer on the PLATO system was a
batch job that routinely got pre-empted by the scheduler, just long enough for its buffer
to go empty. I ended up doing the whole job in PPUs (reading the input file as well as
feeding the printer).
paul
On Feb 16, 2025, at 7:38 PM, Van Snyder via
cctalk <cctalk(a)classiccmp.org> wrote:
.... It also
had a thermal printer called "teledotis." It was very fast, so some
called it the Whippet. It electrostatically deposited soot onto special
paper, which was then fused by a heat roller.
I would call that an "electrostatic printer" -- xerographic printer work that
way, depositing plastic soot that is then melted onto the paper. At U of Illinois I used
a printer very much like what you describe, made by Varian. That was a dot matrix line
printer -- a row of pixels across the page at once -- we used for printing music scores.
100 dpi or so if I remember right.