Home > Tech Explained

What Happens When You Restart Your Computer

By Alexander Fox
What Happens When You Restart Your Computer Featured Image

Restarting your computer is a common task. Whether for troubleshooting or software and hardware installation, most computers get restarted on a fairly regular basis. And those that don’t might start showing problems until they do get restarted. What happens when you restart your computer? It’s actually a fairly simple process involving some pretty basic commands.

What happens when you reboot?

restart-computer-reboot-1

In the abstract, a reboot is indicated by a power state flag set by your computer at the end of the shutdown process. This flag tells the motherboard to reset the attached components using the correct reset commands, then follow the normal startup (AKA “bootstrap”) process.

This reset command is nothing more than a certain value at a certain register address which the motherboard checks before moving to its “off” state. If the reboot flag is present, the computer starts the boot process as soon as the shutdown process is finished. If the flag isn’t present, the computer moves into the “soft off” state, waiting for you to come back and press the power button again.

The reboot process is only slightly different from the shutdown process. The computer “knows” to reboot thanks to the ACPI reset command, but that’s only set after the computer has completed the shutdown process. All components get reset as part of the shutdown process, so the only difference between shutdown and reboot is that the computer restarts immediately.

The shutdown process is pretty simple itself. When you select “shutdown” from the OS menu, the computer quits all apps, does a little housekeeping, unmounts the filesystem and turns off peripheral devices.

What are power states?

restart-computer-reboot-2

Much of your computer’s shutdown and restart processes are controlled by ACPI (advanced configuration and power interface) power states. Power states come in a couple flavors and are controlled by the motherboard. These power states comes fro m ACPI, or Advanced Configuration and Power Interface, which controls power management in your PC. There are a couple important power states that help us understand how the computer operates.

  • G0: Power on and working; your computer’s operational status
  • G1: Sleeping
    • S1: RAM and CPU power stays on, but the CPU isn’t processing instructions. Peripheral devices are powered off.
    • S2: CPU is powered off, but RAM power is maintained, preserving memory contents
    • S3: Everything except RAM and peripherals that can wake the computer, like the keyboard, is powered off. This is your computer’s “sleep” state, which is triggered from the start menu in Windows.
    • S4: RAM contents are written to disk and everything powers off. This is the “hibernate” mode. The only difference between this and G2 is the resume process: you won’t need to boot your PC to return from this power state.
  • G2: “Soft off.” This is the computer’s typical off state. Power is cut to everything except devices that listen for power on.
  • G3: Mechanically off, cannot be started until put back into G2.

Why does rebooting fix so many problems?

Rebooting is a key troubleshooting step because it fixes a huge variety of problems. But how?

During the reboot process, all of the computer’s logic is reset. This means that the CPU, memory, controllers and peripherals all receive their reset commands and return to their boot-up states. By wiping away anything that was happening previously, this reset can often fix problems by resetting things to their “new” state. Of course, this doesn’t mean the problem won’t reoccur. But this fresh start often removes the offending gremlin, at least temporarily.

Subscribe to our newsletter!

Our latest tutorials delivered straight to your inbox

Alexander Fox Avatar
Alexander Fox
Alexander Fox is a tech and science writer based in Philadelphia, PA with one cat, three Macs and more USB cables than he could ever use.

Read next

In 1843, Ada Lovelace described a brass-and-punched-card engine that could act on symbols as well as numbers, even composing music if harmony could be reduced to rules, inside seven translator’s notes three times longer than the paper itself
Bright modern laboratory with computers and technical equipment for research and analysis.
ARPANET sent its first message on 29 October 1969 from a lab at UCLA to a machine at Stanford, and the message was supposed to read ‘LOGIN’ — but the system crashed after the L and the O, meaning the first word ever transmitted over the network that became the internet was, by accident, ‘LO’.
In 1995, Microsoft shipped a cartoon-house interface called Bob, led by Melinda French, who married Bill Gates while it was in development — it demanded twice the memory of a typical home PC, sold roughly 30,000 copies, and was dead within a year, leaving behind the font Comic Sans and the animated assistant that became Clippy.
Stunning underwater shot of tiger sharks swimming among fish in the ocean depths.
The Greenland shark grows about one centimetre a year, does not reach sexual maturity until around age 150, and a specimen carbon-dated by Danish researchers in 2016 was estimated to be at least 272 years old, meaning it was already swimming the North Atlantic when Mozart was composing symphonies.
A person using a smartphone with a green screen surrounded by fresh fruits and vegetables in the kitchen.
When Apple shipped iOS 12 in June 2018, a small feature called Screen Time slipped onto every iPhone with a counter nobody had quite prepared for — a tally of pickups — and within a day Tim Cook was telling CNN the number of times he picked up his own phone was simply too many
Starry night with radio towers and the Milky Way galaxy visible overhead.
When NASA lost contact with the IMAGE satellite in 2005, an amateur radio operator in Canada named Scott Tilley picked up its signal in January 2018 while hunting for a classified spy satellite, and the spacecraft turned out to be still spinning, still powered, and still trying to phone home after 13 years of silence.
Close-up of a smartphone highlighting its modern design on a dark background.
The original iPhone Steve Jobs unveiled in January 2007 could not record video, could not copy and paste text, could not run a single third-party app, and could only reach the internet over 2G — and Jobs spent ninety minutes on stage at Macworld arguing, one missing feature at a time, that every absence was actually a design decision.
In 1965, Joe Sutter’s Boeing team began shaping the 747 around a future they thought would belong to supersonic jets, lifting the cockpit onto a hump so the nose could open for cargo once the giant subsonic passenger plane had outlived its brief moment