computer science

Reset (computing)

Reset (computing) 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 Reset (computing) rather than just read about it. In short: In a computer or data transmission system, a reset clears any pending errors or events and brings a system to normal condition or an initial state, usually in a controlled manner. It is usually done in response to an error condition when it is impossible or undesirable for a processing activity to proceed and all error recovery mechanisms fail.

Key takeaways

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

Reference excerpt

In a computer or data transmission system, a reset clears any pending errors or events and brings a system to normal condition or an initial state, usually in a controlled manner. It is usually done in response to an error condition when it is impossible or undesirable for a processing activity to proceed and all error recovery mechanisms fail. A computer storage program would normally perform a "reset" if a command times out and error recovery schemes like retry or abort also fail.

Software reset

A software reset (or soft reset) is initiated by the software, for example, Control-Alt-Delete key combination have been pressed, or execute restart in Microsoft Windows.

Hardware reset

Most computers have a reset line that brings the device into the startup state and is active for a short time after powering on. For example, in the x86 architecture, asserting the RESET line halts the CPU; this is done after the system is switched on and before the power supply has asserted "power good" to indicate that it is ready to supply stable voltages at sufficient power levels. Reset places less stress on the hardware than power cycling, as the power is not removed. Many computers, especially older models, have user accessible "reset" buttons that assert the reset line to facilitate a system reboot in a way that cannot be trapped (i.e. prevented) by the operating system, or holding a combination of buttons on some mobile devices. Devices may not have a dedicated Reset button, but have the user hold the power button to cut power, which the user can then turn the computer back on. Out-of-band management also frequently provides the possibility to reset the remote system in this way. Many memory-capable digital circuits (flip-flops, registers, counters and so on) accept the reset signal that sets them to the pre-determined state. This signal is often applied after powering on but may also be applied under other circumstances. After a hard reset, the register states of many hardware have been cleared. The ability for an electronic device to reset itself in case of error or abnormal power loss is an important aspect of embedded system design and programming. This ability can be observed with everyday electronics such as a television, audio equipment or the electronics of a car, which are able to function as intended again even after having lost power suddenly. A sudden and strange error with a device might sometimes be fixed by removing and restoring power, making the device reset. Some devices, such as portable media players, very often have a dedicated reset button as they are prone to freezing or locking up. The lack of a proper reset ability could otherwise possibly render the device useless after a power loss or malfunction. User initiated hard resets can be used to reset the device if the software hangs, crashes, or is otherwise unresponsive. However, data may become corrupted if this occurs. Generally, a hard reset is initiated by pressing a dedicated reset button On some systems (e.g, the PlayStation 2 video game console), pressing and releasing the power button initiates a hard reset, and holding the button turns the system off.

Hardware reset in 80x86 IBM PC The 8086 microprocessors provide RESET pin that is used to do the hardware reset. When a HIGH is applied to the pin, the CPU immediately stops, and sets the major registers to these values:

The CPU uses the values of CS and IP registers to find the location of the next instruction to execute. Location of next instruction is calculated using this simple equation: Location of next instruction = (CS<<4) + (IP) This implies that after the hardware reset, the CPU will start execution at the physical address 0xFFFF0. In IBM PC compatible computers, This address maps to BIOS ROM. The memory word at 0xFFFF0 usually contains a JMP instruction that redirects the CPU to execute the initialization code of BIOS. This JMP instruction is absolutely the first instruction executed after the reset.

Hardware reset in later x86 CPUs Later x86 processors reset the CS and IP registers similarly, refer to Reset vector.

Mac Apple Mac computers allow various levels of resetting, including (CTL,CMD,EJECT) analogous to the three-finger salute (CTL,ALT,DEL) on Windows computers.

See also Abnormal end Abort (computing) CRIU Hang (computing) Power-on reset Power-on self test Reboot (computing) Reset vector

References

Worked examples

Example 1 — a first encounter with Reset (computing)

Start with the simplest possible case. Write down what Reset (computing) 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 Reset (computing) 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 Reset (computing) 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 Reset (computing)

In research: Reset (computing) 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 Reset (computing) 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: Reset (computing) is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computing terminology, so understanding it makes those chapters shorter.
In everyday life: Look for Reset (computing) 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 Reset (computing) in 20 minutes

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

Frequently asked questions

What is Reset (computing) in simple terms?

Why does Reset (computing) 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 Reset (computing)?

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 Reset (computing).