computer science

Scratch space

Scratch space 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 Scratch space rather than just read about it. In short: Scratch space is space on the hard disk drive that is dedicated for storage of temporary user data, by analogy of "scratch paper." It is unreliable by intention and has no backup. Scratch disks may occasionally be set to erase all data at regular intervals so that the disk space is left free for future use.

Key takeaways

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

Reference excerpt

Scratch space is space on the hard disk drive that is dedicated for storage of temporary user data, by analogy of "scratch paper." It is unreliable by intention and has no backup. Scratch disks may occasionally be set to erase all data at regular intervals so that the disk space is left free for future use. The management of scratch disk space is typically dynamic, occurring when needed. Its advantage is that it is faster than e.g. network filesystems. Scratch space is commonly used in scientific computing workstations, and in graphic design programs such as Adobe Photoshop. It is used when programs need to use more data than can be stored in system RAM. A common error in that program is "scratch disks full", which occurs when one has the scratch disks configured to be on the boot drive. Many computer users gradually fill up their primary hard drive with permanent data, slowly reducing the amount of space the scratch disk may take up. Partitioning off a significant fraction of the boot hard drive and leaving that space empty will ensure a reliable scratch disk. Hard drive space, on a per-gigabyte basis, is far cheaper than RAM, though performs far slower. Although dedicating a separate physical drive from the main operating system and software can improve performance, a scratch disk will not match RAM for speed.

See also Scratch tape Swap partition Temporary folder TMPDIR

References

Worked examples

Example 1 — a first encounter with Scratch space

Start with the simplest possible case. Write down what Scratch space 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 Scratch space 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 Scratch space 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 Scratch space

In research: Scratch space 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 Scratch space 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: Scratch space is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer files, Computing terminology, Rotating disc computer storage media, so understanding it makes those chapters shorter.
In everyday life: Look for Scratch space 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 Scratch space in 20 minutes

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

Frequently asked questions

What is Scratch space in simple terms?

Why does Scratch space 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 Scratch space?

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 Scratch space.