Storage devices and methods

Abstract

Before the advent of the electronic computer, data that had been stored on punched cards could only be processed very slowly because all the sensing of the hole — or no-hole — environment was done electromechanically by brushes or pins that either made contact through the hole or failed to do so. This was a slow process, and many boxes of cards were necessary for the storage of data. These were prone to many problems, of damp, physical damage or carelessness — dropping a deck of cards caused no end of difficulties! But with the power and speed of the electronic computer and the electromagnetic storage technology used in tape recording it became possible to store and retrieve the very large amounts of data that were stored on reels of magnetic tape with a consequent massive increase in speed of operation. By using magnetic tape it was possible to mimic a deck of punched cards by dividing the tape up into equal length blocks of data of where each block was a record and the data held in that record was held in a series of separate fields. The speed of retrieving the data was comparatively low, since the only way to find a particular record was to start from the first record on the tape and read every record in sequence until the right one was located. Alternatively, if the number of the record was known, then the tape could be wound along to that record. Because all records were of equal length it was simple to count the records as they passed the reading head until the right one appeared. However, there were other problems. If the records had to be sorted then the computer was faced with a very tedious task involving the constant rewinding of tapes.Figure 2.1 shows typical magnetic tape installations.