The IBM Selectric Ball

Early typewriters operated with a series of lever arms, where each arm had a letter form at the end. This made it possible to design manual typewriters that that operated by pressing a key, which directly engaged the lever arm, striking the paper through an inked ribbon, typing a letter. The drawback to these lever arms was that if an operator pressed multiple keys at the same time, such as when mistyping—or even if typing really fast, so that one lever arm doesn't "drop" fast enough before the next comes up—the lever arms could jam.

In the era of the electric typewriter, one solution was the Daisy Wheel, or sometimes just the Wheel. This also used lever arms, but arranged on a wheel; the travel distance for any lever arm was not very far. When the user pressed a key, electronics in the typewriter spun the Wheel so the correct letter appeared in the typing position, then a small solenoid struck the lever arm, thus typing a letter.

One typewriter that used a Daisy Wheel was the IBM 6747 electric typewriter. If you'd like to see it in action, watch this brief video of the IBM 6747-2 Daisy Wheel typewriter printing normal speed and in "slow mo," showing the typing mechanism in action. (video is from the Hursley Museum, which preserves IBM systems developed at the Hursley Park location)

A benefit to the Wheel was that the type wheel was usually interchangeable. To print in a different typestyle, such as from roman to italic, the user replaced the Daisy Wheel. Although this could be more difficult than it seems, depending on model, because the Wheel could be mounted well inside the typewriter body.

IBM's Selectric typewriter used a chrome-plated plastic "ball" (called a "type ball," or informally as the "golf ball," or sometimes just the "Ball") that could quickly rotate left-right and up-down to strike the paper with the typed character. And it could do so very quickly, as demonstrated in another video from the Hursley Museum, showing the IBM Selectric "golf ball" in motion in both normal speed and "slow mo."

The Ball printing element was easily interchangeable, by pressing two spring handles together to remove the Ball, then click another Ball into place. IBM advertised that changing to a new typeface Ball was as fast as five seconds.

The original IBM Selectric typewriter was introduced in 1961, and was called simply the "Selectric." The IBM Selectric II typewriter (1971) supported both 10 and 12 characters per inch. The Selectric II sold very well and became the base model for other IBM typing devices including the Correcting Selectric (with a correcting ribbon) and Selectric Composer (used in typesetting). The IBM Selectric III typewriter (1980) was the last of the "Selectric" line, until it was spun off to Lexmark in 1991.