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Intelligent Machines

Why Don’t Computers Boot Up Instantly?

Computers still require a phoenix-like rebirth after every little death that comes with a shutdown.

It doesn’t take a few minutes to boot up your computer anymore, but it’s also still far from instantaneous. Even with modern, super-fast electronics, there’s a delay before you can start doing something. What’s holding things up?

Walk, then run

A computer is an inert hunk of electronics until you press the power button. From that moment, all its parts are prodded and agree to start up. These low-level actions take place in sequence before its operating system is loaded and other actions, as well as applications, become available.

First, some amount of throat-clearing occurs before any instruction is loaded. As the power starts flowing, specialized chips ensure that voltages are correct and stable. Clocks, the built-in timers that keep everything running at different cadences like coxswains on racing sculls, have to start counting off millions or billions of times per second. Processors that handle certain peripherals, like keyboards or networks, perform their own quick boot.

Next, the central processing unit (CPU) wakes and starts running a bootloader, software that figuratively pulls a computer up by its own bootstraps. The notion of booting has its roots all the way back in the 1950s. Since the 1970s, most CPUs have looked to a particular predefined location in nonvolatile memory (memory that persists without power), where it can pull in the first program code. From the dawn of PCs, that bootloader was BIOS (basic input/output system). Computers from Apple and other makers had their own equivalents, all of which test and prepare the hardware. If all is well, the BIOS begins to load the operating system, which in modern versions takes over all the functions the BIOS provided during boot, and you’re on your way.

Every stage introduces delays, but those have been diminishing in the last three years. BIOS has been largely replaced, solid-state drives (SSDs) have improved performance, and extremely low-power sleep or hibernation states have bypassed the need for a reboot at all.

Revamped software

Replacing BIOS has had a noticeable effect. The effort began in 1998, when Intel got to work on a standard now called UEFI (Universal Extensible Firmware Interface). UEFI is more efficient code made for modern processors. It also prioritizes tasks in a better order for the vast majority of users. It delays the lengthy startup of systems that hardly anyone needs right away and instead favors the loading of drivers to get a video display up and running. This also gives users earlier indications that progress toward boot-up is occurring. Ideally, they quickly get a sense of “Ah, it’s working! I know it’s alive,” says Michael Krau, who chairs the industry communications work group at the UEFI Forum, the standards group that administers the technology.

While UEFI has already clawed out many improvements, the group continues to work on shaving off milliseconds and more. “If we could push the button so that it would come on in zero seconds, that would be wonderful,” says Krau.

Shaving off seconds

Meanwhile, OS makers have been working for years to decrease the time between the handoff from the bootloader and the appearance of a log-in screen or fully functional operating environment. Windows can still take 30 to 60 seconds to start up the first time, but Windows 8 shaved subsequent boots significantly through a little trick. PCs have long offered a variety of sleep states, in which the state of a computer’s operations is written to a hard drive, SSD, or flash memory, allowing a faster recovery than a reboot provides. Windows 8.1, which appeared in 2013, added a variant. A user can select “fast startup,” which means that when the computer is shut down, not only the computer’s state but also much of the setup needed for the operating system to function is stored on a hard drive or SSD. On the next startup, the UEFI boot still happens, but the OS portion occurs more quickly, so a “fast startup” can take eight to 15 seconds.

The takeaway:

By all accounts, there’s more efficiency to be wrung, and a seemingly instant-on boot isn’t impossible, especially with even more efficient storage technologies.

Thanks to Jorge Soares for this week’s question. If you have one, send suggestions to questionoftheweek@technologyreview.com

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