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<p>Yes, and until ~ the 1442, the IBM readers used a row of metal
brushes to read the cards (they'd go through the holes and contact
a metal plate on the bottom). All the early IBM gear was
mechanically interesting - I suppose from their origins. Springs,
brushes, cams, levers, solenoids, microswitches, belts and
motors! A mechanical engineering degree was probably more helpful
than an EE (or later CS)...</p>
<p>The 1442 (ish) introduced optical (incandescent lamp + photocell)
readers; Documation also was optical. IIRC, it also had a taller
path, so was more tolerant of warpage/curled edges. Toward the
end, the light source became LEDs. <br>
</p>
<p>Anything that avoided contact with the cards helped reliability.
The challenge for the designers was to have tolerances large
enough to avoid jams, but small enough to prevent picking more
than one card, or allowing skew in transit.</p>
<p>The off-line card sorters and reproducing punches (with the wired
plugboards, often used with mark-sense) were also mechanical
marvels - or monsters - depending on which side of the Field
Engineers' toolbox you stood.<br>
</p>
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<div class="moz-cite-prefix">On 13-Feb-20 13:00, Paul Koning wrote:<br>
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cite="mid:8E009812-6163-4D0D-917C-E9069CE7F141@comcast.net">
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<pre class="moz-quote-pre" wrap="">On Feb 13, 2020, at 12:17 PM, Robert Thomas <a class="moz-txt-link-rfc2396E" href="mailto:rft@asthomas.com"><rft@asthomas.com></a> wrote:
...
The Documation card reader was fairly reliable and didn't chew up as many cards as the IBM reader.
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I can believe that. The IBM card readers and punches I've seen (on a 360/44) had a pick mechanism that moves a metal block with a small step in it, sized to match the nominal thickness of the card. This was supposed to catch the far edge of the card and *push* it into the throat of the feed mechanism. If there was anything slightly wrong, it would accordeon-fold the card instead.
The Documation readers had vacuum operated pick mechanisms that acted on the leading edge of the card.
paul
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