Employing Magnets for Computer Technology
In the April 1955 issue of Electronic Design (Vol. 3 No. 4), an intriguing technology was spotlighted: magnetic core logic. This innovative approach, used for logic functions in some early computing systems, was based on magnetic logic gates that employed magnetic cores with multiple wire windings.
The advantages of magnetic core logic were significant, setting it apart from other two-state components such as vacuum tubes or early transistors. For one, the magnetic cores boasted a virtually infinite lifetime due to their lack of wear-out issues like vacuum tubes, and they avoided the variability problems of early transistors. Moreover, the cores offered solid-state reliability, as they had no moving parts and were less sensitive to mechanical shock or heat than vacuum tubes. Additionally, the non-volatility of the magnetic cores was advantageous for memory and some logic applications, as they retained their state without power.
However, magnetic core logic did have its drawbacks. Compared to vacuum tubes or transistors, magnetic core logic operated at slower speeds due to the longer time it takes for changes in magnetic state. Furthermore, complex drive pulses, usually generated by vacuum tubes as current amplifiers, complicate circuitry and limit overall speed improvements. Lastly, the larger physical size and complexity of magnetic cores made dense integration difficult.
Despite these limitations, magnetic-core technology provided an intermediate solution offering durability and solid-state reliability, particularly for memory but also for some logic applications. However, it was eventually eclipsed by transistor and later integrated circuit technology that offered much higher speed, smaller size, and easier scaling.
One of the key components of magnetic core logic was the magnetic core shift register, which could perform functions such as operating over a range of pulse rates, accepting parallel or serial information, complementing, inserting, or shifting stored information in buffer memories. The shift register memory had an initial access time of 0.2-microsec and a repeated access time of less than 2 microsec, while the coincident current memory had an initial access time of one and a repeated access time of less than 7 microsec.
The magnetic core logical element, designed to be a low impedance, low-power device, was still limited by pulse rate, power level, and the choice of diodes. The "Single Line" magnetic core logical element, in particular, had a reliability similar to the "Single Line" magnetic shift register.
The article also discussed the use of magnetic core circuits for computer functions beyond storage. Magnetic cores were being used as a different type of logical element or gate in selection systems, and several laboratories were developing saturable transformers, biased cores, and time-pulse sequence gates for use in magnetic circuits and selection systems.
Robert D. Kodis, Head of Research and Development Section, Computer Dept. at Raytheon Manufacturing Co., Waltham, Mass., was one of the pioneers in this field. His work contributed to the understanding and development of magnetic core technology, which, although eventually surpassed by more advanced technologies, played a crucial role in the early days of computing.
A simple example of a magnetic core application is a binary-to-binary coded decimal converter and binary coded decimal to binary, which could convert over 1000 decimal digits per second using 100 cores. Furthermore, magnetic shift registers using selenium diodes have had over 20,000 hours of operation, while those using germanium, gold-bonded diodes have operated for over 8,000 hours with no measurable changes in their operating characteristics or output signals.
In conclusion, magnetic core technology, with its unique advantages and limitations, marked an important step in the evolution of computing. Although it has been largely replaced by more modern technologies, its pioneering role in solid-state computing cannot be understated.
Gadgets showcasing data-and-cloud-computing capabilities often incorporate advanced technology, such as the magnetic core shift register, a key component of an intermediate but significant technology in early computing systems. This historical technology, known as magnetic core logic, was valuable due to its durability, solid-state reliability, and non-volatility despite slower speeds and larger physical size compared to other technologies that emerged later.
