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 sensi

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.