Re:IBM Punched Card Typography
by kens on Monday January 30, 2017 @07:05PM
(#13526237)
Very interesting article. Stepping back, you might wonder why the keypunch uses a metal plate to hold the character bitmaps rather than a ROM or something sensible. Remember that the 026 keypunch was introduced in 1949, so there wasn't really a convenient way to store bits. It's actually pretty clever to use bumps on a metal plate to drive the printing.
The other side of this is how they stored the mapping from keys to hole patterns, with each key punching 0 to 3 holes. This was also done mechanically. Each key moved a lever ("bail") with tabs, and the tabs trip contacts that cause the right holes to be punched. But in between is a bunch of relay-based logic to handle shifting for special characters, numeric keypad mode, and so forth.
If you want to try out a 026 keypunch yourself, go to the Computer History Museum in Mountain View CA when they are demoing the IBM 1401.
The other side of this is how they stored the mapping from keys to hole patterns, with each key punching 0 to 3 holes. This was also done mechanically. Each key moved a lever ("bail") with tabs, and the tabs trip contacts that cause the right holes to be punched. But in between is a bunch of relay-based logic to handle shifting for special characters, numeric keypad mode, and so forth.
If you want to try out a 026 keypunch yourself, go to the Computer History Museum in Mountain View CA when they are demoing the IBM 1401.