What are these IBM 'thingys'
dm561 at torfree.net
Tue Oct 26 14:18:37 CDT 2010
Date: Tue, 26 Oct 2010 10:28:12 +0100
From: Roger Holmes <roger.holmes at microspot.co.uk>
Subject: Re: What are these IBM 'thingys'
> From: Al Kossow <aek at bitsavers.org>
> On 10/25/10 7:26 PM, leaknoil wrote:
>> It looks to me like a punch card exactly fits in there and the contacts
>> are what read the holes in the card.
> cards are read with 12 brushes
Or 80 brushes, I think the holes in cards were made tall and narrow to make
reading them that way easier.
Exactly. In those electro-mechanical days cards were almost always read in
parallel, i.e. long edge first, because that's how those machines worked;
rotary selectors, type bars, sorter gates, etc., the timing of the entire
system was based on and ran in sync with the card moving through the various
digit positions 0 to 9 (and 11 & 12 for symbols and alpha).
Want to add two numbers? Take a rotary 10-position switch and connect it
mechanically through a solenoid-operated clutch so that as the card moves so
does the switch, each position corresponding to a vertical location on the
card. Starting with the switch in the 0 position, read the first card,
engage the clutch when it passes the 0 position and drop the clutch when a
brush makes contact through a hole in the card. Do the same with the second
card and the rotary switch will read the sum (with a few extra solenoids and
relays to handle carries).
Want to print it? Simple: you have a type bar with the digits in reverse
order, again synchronized to the rest of the machine. Start rotating the
switch and moving the type bar together and when the switch hits 0 fire the
Want to sort your invoices by client number? Take the card deck over to your
08x sorter, those machines you've all seen in old movies where the cards
move across and drop into different columns or pockets (usually flying out
and across the room for amusement - it wasn't funny when it really did
happen!). Rotate the column selector knob to the LSD column (it only had one
moveable brush) and press Start. As the card moves, it passes a set of
chutes each leading to one of those pockets and when the brush makes contact
through the hole the card is diverted to whichever chute it's under at that
exact moment. Go through all the cards, put the 10 piles back together in
sequence, repeat for each column up to the MSD and presto, they're sorted.
Ah, the good old days... I'd love to see some kind of emulation of these
When computers came along the whole paradigm shifted from parallel
processing to serial, and those card readers did indeed read the card from
left to right with only 12 brushes (more likely optical sensors) instead of
top to bottom with 80, although IIRC there were some combined serial and
parallel binary card formats.
Of course now we've seen the error of our ways and have returned to parallel
processing; a modern card reader would no doubt read cards top to bottom
again, with each column connected to its own CPU.
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