The Input Unit

The Input Unit

Input Unit Cards or paper tape with their punched holes are placed in the input unit of the computer. Here, the computer's reading mechanism translates the patterns of holes into electrical pulses.
The cards are read at speeds around 1,000 cards per minute, and paper tape at around 1,000 characters per second. As the processing speeds are measured in nano- seconds (one thousand millionths of a second) these are both termed slow input devices. The reading may be done with light which shines through the holes and strikes a layer of photo-electric cells which turn the light dots into electrical pulses. Or cards can be passed between a roller conducting electricity and a series of tiny wire contacts. Where the holes appear the contacts momentarily touch the conductor and an electrical pulse is flashed into the machine. Where there is no hole there will, of course, be no electrical pulse produced; thus the coded pattern is turned into a series of pulses and no-pulses.
Document readers, or character recognition systems, can use photo-electric sensing on the shape of a written character as in electricity accounts. On cheques the magnetic pattern of the character is detected. These systems do not allow direct input into the computer but they do give an accurate method of reading data. They are first punched by an operator using a keyboard similar to that of an ordinary typewriter.
Visual Display Units (VDUS) are also important input devices. The keyboards to VDUs are similar to those of typewriters, and data input can be displayed on the screen. This method of reading data is used at Ladybird Books to check and record orders for books.

Reproduced from "How it Works" Ladybird Series