computer science

IBM drum storage

IBM drum storage 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 drum storage rather than just read about it. In short: In early computers drum storage consisted of a large metal cylinder coated on the outside surface with a ferromagnetic recording material, to provide random access for stored data. Drums were later largely replaced by the hard disk drive.

Key takeaways

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

Reference excerpt

In early computers drum storage consisted of a large metal cylinder coated on the outside surface with a ferromagnetic recording material, to provide random access for stored data. Drums were later largely replaced by the hard disk drive. Drums were used as main memory by IBM in computers including the IBM 305 and IBM 650; IBM also offered drum devices as secondary storage for the 700/7000 series and System/360 series of computers.

IBM 731 The IBM 731 is a discontinued storage unit used on the IBM 701. It has a storage capacity of 2,048 36-bit words (9,216 8-bit bytes).

IBM 732 The IBM 732 is a discontinued storage unit used on the IBM 702. It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes).

IBM 733 The IBM 733 is a discontinued storage unit used on the IBM 704 and IBM 709. It has a storage capacity of 8192 36-bit words (36,864 8-bit bytes).

IBM 734 The IBM 734 is a discontinued storage unit used on the IBM 705 It has a storage capacity of 60,000 6-bit characters (45,000 8-bit bytes).

IBM 7320 The IBM 7320 is a discontinued storage unit manufactured by IBM which was announced on December 10, 1962 for the IBM 7090 and 7094 computer systems, was retained for the earliest System/360 systems as a count key data device, and was discontinued in 1965. The 7320 is a vertically mounted head-per-track device with 449 tracks, 400 data tracks, 40 alternate tracks, and 9 clock/format tracks. The rotational speed is 3,490 rpm, so the average rotational delay is 8.6 milliseconds. Attachment to a 709x system is through an IBM 7909 Data Channel and an IBM 7631 File Control unit, which can attach up to five random-access storage units: a mix of 7320, 1301, and 1302 DASD. One or two 7631 controllers can attach to a computer system, but the system can still attach only a total of five DASD. When used with a 709x, a track holds 2,796 6-bit characters, and a 7320 unit holds 1,118,400 characters. Data transfer rate is 202,800 characters per second. The 7320 attaches to a System/360 computer through a channel and an IBM 2841 Storage Control unit. Each 2841 can attach up to eight 7320 devices. When used with System/360, a track holds 2,081 8-bit bytes, and a 7320 unit holds 878,000 bytes. Data transfer rate is 135,000 bytes per second. The 7320 was superseded by the IBM 2301 in mid-1966.

IBM 2301 The IBM 2301 is a magnetic drum storage device introduced in the late 1960s to "provide large capacity, direct access storage for IBM System/360 Models 65, 67, 75, or 85." The vertically mounted drum rotates at around 3,500 revolutions per minute, and has a head-per-track access mechanism and a capacity of 4 MB. The 2301 has 800 physical tracks; four physical tracks make up one logical track which is read or written as a unit. The 200 logical tracks have 20,483 bytes each. The average access time is 8.6 ms, and the data transfer rate is 1,200,000 bytes per second. The 2301 attaches to a System/360 via a selector channel and an IBM 2820 Storage Control Unit, which can control up to four 2301 units.

IBM 2303 The IBM 2303 is a magnetic drum storage device with the same physical specifications as the IBM 2301. The difference is that the 2303 reads and writes one physical track at a time, rather than the four in the 2301, reducing the data transfer rate to 312,500 bytes per second. The 2303 attaches to System/360 through a channel and an IBM 2841 Storage Control Unit, which can attach up to two 2303 units.

See also Drum memory: Drums used as main memory

Notes

References

Worked examples

Example 1 — a first encounter with IBM drum storage

Start with the simplest possible case. Write down what IBM drum storage 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 drum storage 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 drum storage 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 drum storage

In research: IBM drum storage 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 drum storage 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 drum storage is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer storage devices, History of computing hardware, IBM storage devices, so understanding it makes those chapters shorter.
In everyday life: Look for IBM drum storage 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 drum storage in 20 minutes

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

Frequently asked questions

What is IBM drum storage in simple terms?

Why does IBM drum storage 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 drum storage?

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 drum storage.