computer science

Magnetic logic

Magnetic logic is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Magnetic logic rather than just read about it. In short: Magnetic logic is digital logic made using the non-linear properties of wound ferrite cores. Magnetic logic represents 0 and 1 by magnetising cores clockwise or anticlockwise.

Key takeaways

Magnetic logic belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Magnetic logic to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Magnetic logic from memory before moving on to harder problems.

Reference excerpt

Magnetic logic is digital logic made using the non-linear properties of wound ferrite cores. Magnetic logic represents 0 and 1 by magnetising cores clockwise or anticlockwise. Examples of magnetic logic include core memory. Also, AND, OR, NOT and clocked shift logic gates can be constructed using appropriate windings, and the use of diodes. A complete computer called the ALWAC 800 was constructed using magnetic logic, but it was not commercially successful. The Elliott 803 computer used a combination of magnetic cores (for logic function) and germanium transistors (as pulse amplifiers) for its CPU. It was a commercial success. William F. Steagall of the Sperry-Rand corporation developed the technology in an effort to improve the reliability of computers. In his patent application, filed in 1954, he stated:

"Where, as here, reliability of operation is a factor of prime importance, vacuum tubes, even though acceptable for most present-day electronic applications, are faced with accuracy requirements of an entirely different order of magnitude. For example, if two devices each having 99.5% reliability response are both utilized in a combined relationship in a given device, that device will have an accuracy or reliability factor of .995 × .995 = 99%. If ten such devices are combined, the factor drops to 95.1%. If, however, 500 such units are combined, the reliability factor of the device drops to 8.1%, and for a thousand, to 0.67%. It will thus be seen that even though the reliability of operation of individual vacuum tubes may be very much above 99.95%, where many thousands of units are combined, as in the large computers, the reliability factor of each unit must be extremely high to combine to produce an error free device. In practice of course such an ideal can only be approached. Magnetic amplifiers of the type here described meet the necessary requirements of reliability of performance for the combinations discussed." Magnetic logic is able to achieve switching speeds of about 1MHz but was overtaken by semiconductor based electronics which is able to switch much faster. Solid state semiconductors were able to increase their density according to Moore's law, and thus proved more effective as IC technology developed. Magnetic logic has advantages in that it is not volatile, it may be powered down without losing its state.

See also Electropermanent magnet Magnetic amplifier Parametron Hewitt Crane

References

Worked examples

Example 1 — a first encounter with Magnetic logic

Start with the simplest possible case. Write down what Magnetic logic claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Magnetic logic before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Magnetic logic ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Magnetic logic

In research: Magnetic logic appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Magnetic logic in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Magnetic logic is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1954 in computing, Logic gates, Magnetic logic computers, so understanding it makes those chapters shorter.
In everyday life: Look for Magnetic logic outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Magnetic logic in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Magnetic logic means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Magnetic logic out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Magnetic logic in simple terms?

Magnetic logic is digital logic made using the non-linear properties of wound ferrite cores. Magnetic logic represents 0 and 1 by magnetising cores clockwise or anticlockwise.

Why does Magnetic logic matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Magnetic logic?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Magnetic logic.