A Laboratory Model Magnetic Drum Translator for Toll Switching Offices

The magnetic drum is one of the most widely used of the modern largecapacity digital-data storage devices. It is used as a memory unit in many of the present-day large-scale digital computers and in other applications such as inventory control of airline ticket reservations and traffic control of airplanes in flight. Two of the properties of drums as storage media have been considered particularly advantageous. One is the capacity to store up to several hundred thousand bits of information in a compact space at a low cost per bit; the other is the ability to keep the information in an easily alterable but nonvolatile form unaffected by power failure or other interruptions of operation. In terms of the speed with which information may be stored or recovered, drum memories fall near the middle of the present-day spectrum; they are very much faster than punched paper tape or groups of telephone relays but are considerably slower than cathode-ray tube or ferromagnetic-core storage devices. All of the information stored on a drum may be read out during the course of one complete revolution and, similarly, new information may be entered anywhere in the storage space within the time of one revolution; thus the access time is ordinarily of the order of a few tens of milliseconds. It has already been pointed out 1 that automatic telephone switching 707