computer science

I/O request packet

I/O request packet 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 I/O request packet rather than just read about it. In short: I/O request packets (IRPs) are kernel mode structures that are used by Windows Driver Model (WDM) and Windows NT device drivers to communicate with each other and with the operating system. They are data structures that describe I/O requests, and can be equally well thought of as "I/O request descriptors" or similar.

Key takeaways

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

Reference excerpt

I/O request packets (IRPs) are kernel mode structures that are used by Windows Driver Model (WDM) and Windows NT device drivers to communicate with each other and with the operating system. They are data structures that describe I/O requests, and can be equally well thought of as "I/O request descriptors" or similar. Rather than passing a large number of small arguments (such as buffer address, buffer size, I/O function type, etc.) to a driver, all of these parameters are passed via a single pointer to this persistent data structure. The IRP with all of its parameters can be put on a queue if the I/O request cannot be performed immediately. I/O completion is reported back to the I/O manager by passing its address to a routine for that purpose, IoCompleteRequest. The IRP may be repurposed as a special kernel APC object if such is required to report completion of the I/O to the requesting thread. IRPs are typically created by the I/O Manager in response to I/O requests from user mode. However, IRPs are sometimes created by the plug-and-play manager, power manager, and other system components, and can also be created by drivers and then passed to other drivers. The I/O request packet mechanism is also used by Digital Equipment Corporation's VMS operating system, and was used by Digital's RSX-11 family of operating systems before that. An I/O request packet in RSX-11 is called a directive parameter block, as it is also used for system calls other than I/O calls.

Worked examples

Example 1 — a first encounter with I/O request packet

Start with the simplest possible case. Write down what I/O request packet 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 I/O request packet 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 I/O request packet 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 I/O request packet

In research: I/O request packet 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 I/O request packet 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: I/O request packet is common in secondary-school and first-year university syllabi. It links to neighbouring topics Data structures by computing platform, Device drivers, Microsoft Windows stubs, so understanding it makes those chapters shorter.
In everyday life: Look for I/O request packet 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.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study I/O request packet in 20 minutes

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

Frequently asked questions

What is I/O request packet in simple terms?

Why does I/O request packet 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 I/O request packet?

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 I/O request packet.