IBM

Overview

Covered better elsewhere.

Keypunch units

The IBM 024 keypunch and 026 printing keypunch units introduced in 1949 used electromechanical encoding for the keyboards. The later 029 keypunch unit employed an enhanced version of the same type of keyboard.

Details of the keyboard can be found at the following locations:

• Repairing a 1960s-era IBM keypunch: controlled by mechanical tabs and bars
• Documentation at Bitsavers for the 024 and 026
• The IBM 029 keypunch mechanical keyboard: insanely complicated!

Each key is connected to a notched vertical bar, described as “permutation bars”. The notches in this bar engage with projections—“tabs”—on horizontal bars known as “bails”. The presence or absence of a tab on a bail at the position of each key determines which bails are rotated by the respective permutation bar when a key is pressed. The bails in turn operate switches. The complete mechanism is a lot more complicated than this, but the actual encoding is formed solely from the engagement of the permutation bars and bails.

The interlock (that prevents two keys being depressed at once) uses washers rather than ball bearings. Non-encoding keys use straightforward microswitches.