computer science

Harvard Mark III

Harvard Mark III 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 Harvard Mark III rather than just read about it. In short: The Harvard Mark III, also known as ADEC (for Aiken Dahlgren Electronic Calculator) was an early computer that was partially electronic and partially electromechanical. It was built at Harvard University under the supervision of Howard Aiken for use at Naval Surface Warfare Center Dahlgren Division.

Key takeaways

Harvard Mark III 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 Harvard Mark III to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Harvard Mark III from memory before moving on to harder problems.

Reference excerpt

The Harvard Mark III, also known as ADEC (for Aiken Dahlgren Electronic Calculator) was an early computer that was partially electronic and partially electromechanical. It was built at Harvard University under the supervision of Howard Aiken for use at Naval Surface Warfare Center Dahlgren Division.

Technical overview The Mark III processed numbers of 16 decimal digits (plus sign), each digit was encoded by four bits, though using a form of encoding that is different to conventional binary-coded decimal today. Numbers were read and processed serially, meaning one decimal digit at a time, but the four bits for the digit were read in parallel. The instruction length, however, was 38 bits, read in parallel. It used 5,000 vacuum tubes and 1,500 crystal diodes. It weighed 10 tons. It used magnetic drum memory of 4,350 words. Its addition time was 4,400 microseconds and the multiplication time was 13,200 microseconds (times include memory access time). In 1950, Aiken claimed that the Mark III was the slowest electronic computer in the world. Like the previous computers overseen by Aiken, the Mark III was not stored-program. The Mark III used nine magnetic drums (one of the first computers to do so). One drum could contain 4,000 instructions and has an access time of 4,400 microseconds. The arithmetic unit could access two other drums – one contained 150 words of constants and the other contained 200 words of variables. Both of these drums also had an access time of 4,400 microseconds. This separation of data and instructions is now sometimes referred to as the Harvard architecture although that term was not coined until the 1970s (in the context of microcontrollers). There were six other drums that held a total of 4,000 words of data, but the arithmetic unit could not access these drums directly. Data had to be transferred between these drums and the drum the arithmetic unit could access via registers implemented by electromechanical relays. This was a bottleneck in the computer and made the access time to data on these drums long – 80,000 microseconds. This was partially compensated for by the fact that twenty words could be transferred on each access. The Mark III was finished in September 1949 and delivered to the U.S. Naval Proving Ground at the U.S. Navy base at Dahlgren, Virginia in March 1950. Rebuilding the computer in its new location took the remainder of the year. It became operational in 1951, and was being operated 24 hours a day, 6 days a week by October.

References

Further reading A History of Computing Technology, Michael R. Williams, 1997, IEEE Computer Society Press, ISBN 0-8186-7739-2

External links BRL report, 1955 - see ADEC

Illustrations

Worked examples

Example 1 — a first encounter with Harvard Mark III

Start with the simplest possible case. Write down what Harvard Mark III 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 Harvard Mark III 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 Harvard Mark III 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 Harvard Mark III

In research: Harvard Mark III 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 Harvard Mark III 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: Harvard Mark III is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1950s computers, Computer-related introductions in 1951, Electro-mechanical computers, so understanding it makes those chapters shorter.
In everyday life: Look for Harvard Mark III 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 Harvard Mark III in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Harvard Mark III 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 Harvard Mark III out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Harvard Mark III in simple terms?

Why does Harvard Mark III 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 Harvard Mark III?

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 Harvard Mark III.