Prior to word processors, typewriters were commonly used to create typed documents. Typewriters typically have a familiar design. This includes a keyboard on which one or two letters or symbols are represented on each key. Each key has a bar with the indentation of a letter or symbol marked on its edge. Each bar key typically has two or three different markings, each corresponding to the small or capitalized version of a specific letter or a symbol, such as a punctuation mark or number. The typewriter also includes a rubber roll, called a platen, which is located at the head of the typewriter, just above the bar keys, and a roll of ribbon or carbon tape that passes through an aperture onto which the bar keys are struck. Both the platen and the ribbon are placed in a way in which the keys will strike the paper, leaving an inky indentation of characters.
While the function of the typewriter might seem simple, there are a number of different processes occurring at the same time that make the machine function efficiently. First a sheet of paper is placed then rolled into the platen, using a turning dial at the end of the platen. Adjustments for indentation and paper margins are then set, using metal markers that are found along a ruler just beneath the platen. This sets limitation for the typewriter when it moves from one end to the next. When a key is struck, the pressure of the movement causes the corresponding bar to strike the ribbon of ink. This force then leaves an impression on the paper with the corresponding character. As each key is struck, the platen moves horizontally so that the position of the paper moves from right to left. This allows the typist to create a series of words and sentences across a single line. When the platen reaches the page margin, the machine will make a ringing sound, alerting the typist to push the platen to its original position. A lever also allows the platen to shift vertically to begin the next row on the paper. This lever is pressed at the same time the platen is pushed back into position. Therefore, the platen moves horizontally, then vertically, until the entire margins of the paper are filled.
Typewriters also have shift mechanisms which enable the writer to press different characters on the same bar key. The shift tabs are usually found at each end of the keyboard. When pressed, the position of the bar key shifts, thus positioning itself once it strikes the ribbon. The tab key is pressed at the same time a key is struck. This lifts the bar key so that the indentation on the key will be placed in the correct position once it strikes the ribbon. Tab keys are used when a capitalized letter or symbol needs to be struck.
Patented in 1868, typewriters were a common writing machine in both homes and offices. The earliest portable typewriters were invented during the 1920s. Early typewriters were often manual, but by the 1960s, electric typewriters soon gained prominence. Later versions also used balls or daisy wheels instead of keys. These typewriters allowed the platen to remain stationary while a ball or daisy wheel, once pressed by any key on the keyboard, moved from left to right along the paper.