computer science

IBM 2821 Control Unit

IBM 2821 Control Unit 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 IBM 2821 Control Unit rather than just read about it. In short: The IBM 2821 Control Unit attaches card readers and card punches, and line printers to the IBM System/360 and IBM System/370 families of computers. The devices attached may be a combination of: The IBM 2540 card reader and card punch; The IBM 1403 models 2, 3, 7 and N1 line printer; and The IBM 1404 model 2 line printer and bill feed printer.

Key takeaways

IBM 2821 Control Unit 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 IBM 2821 Control Unit to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of IBM 2821 Control Unit from memory before moving on to harder problems.

Reference excerpt

The IBM 2821 Control Unit attaches card readers and card punches, and line printers to the IBM System/360 and IBM System/370 families of computers. The devices attached may be a combination of:

The IBM 2540 card reader and card punch; The IBM 1403 models 2, 3, 7 and N1 line printer; and The IBM 1404 model 2 line printer and bill feed printer. The 2821 was originally advertised—in 1964, before System/360 shipped—as a controller for the IBM 1402 card reader/punch and the IBM 1403 and IBM 2201 printers. Six models of the IBM 2821 Control Unit were available, as follows:

Model 1 attaches one IBM 2540 and one IBM 1403; Model 2 attaches one IBM 1403; Model 3 attaches two or three IBM 1403s; Model 4 attaches one IBM 2540 and one IBM 1404, but only on IBM System/360 models 25, 30, 40 and 50; Model 5 attaches one IBM 2540 and two or three IBM 1403s; and Model 6 attaches one IBM 2540. The 2821 is fully buffered, that is it has buffers large enough to hold an entire card to punch, an entire card read, or an entire print line for each attached device. This frees the channel from having to meet the peripheral devices' tight timing requirements. The control unit can be connected to either a byte multiplexer channel or a selector channel. It is made up of logically independent control units, but takes up only one of the eight control unit slots which can be connected to a channel. A two-channel switch is available, allowing the control unit to be connected to two channels, on one or two computer systems, controlled by manual switches or by programming. The circuitry in the 2821 is largely older-technology IBM SMS, unlike much of the System/360 line, but later revisions were partially implemented in SLT or MST. As logic became cheaper, the functions of the 2821 were increasingly moved inboard to the central processor or outboard to the individual device. The 2821 was withdrawn from marketing in the United States in 1985.

References

External links IBM (November 1969). IBM 2821 Component Description (PDF). Eighth Edition. A24-3312-7. Retrieved 2018-03-18. IBM (October 1982). IBM 2821 Component Description (PDF). Tenth Edition. GA24-3312-9. Retrieved 2018-03-18. uniservo (30 June 2017). "Youtube walkthrough of a late IBM 2821 model 2". YouTube. Retrieved 2018-03-18.

Illustrations

Worked examples

Example 1 — a first encounter with IBM 2821 Control Unit

Start with the simplest possible case. Write down what IBM 2821 Control Unit 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 IBM 2821 Control Unit 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 IBM 2821 Control Unit 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 IBM 2821 Control Unit

In research: IBM 2821 Control Unit 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 IBM 2821 Control Unit 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: IBM 2821 Control Unit is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer hardware stubs, IBM mainframe peripherals, so understanding it makes those chapters shorter.
In everyday life: Look for IBM 2821 Control Unit 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 IBM 2821 Control Unit in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what IBM 2821 Control Unit 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 IBM 2821 Control Unit out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is IBM 2821 Control Unit in simple terms?

The IBM 2821 Control Unit attaches card readers and card punches, and line printers to the IBM System/360 and IBM System/370 families of computers. The devices attached may be a combination of: The IBM 2540 card reader and card punch; The IBM 1403 models 2, 3, 7 and N1 line printer; and The IBM 140…

Why does IBM 2821 Control Unit 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 IBM 2821 Control Unit?

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 IBM 2821 Control Unit.