Windows 10, the biggest update Microsoft has made to its computer software, is now available in the UK.
PC users across the country stayed awake to start their downloads in the early hours of the morning as Microsoft began to roll out the upgrade.
The new software will be the first to work across all Windows-powered devices, from smartphones to tablets and desktop computers, as well as Microsoft's Xbox One games console.
Microsoft is also introducing a new web browser - Edge - to replace Internet Explorer, while the firm's voice assistant Cortana will also move to desktop computers for the first time.
The much-loved Start menu, which was removed in Windows 8 to much public outcry, is also making a return in the new software, as the US-firm looks to modernise and appeal to a new range of customers.
Early reaction has so far been positive, though some users have take to social media to express frustration at the time taken to install the update.
However, Will Findlater, technology expert and editor in chief of gadget magazine Stuff says the upgrade is worth it.
"With Windows 10, Microsoft appears to be taking the best bits of Windows 8, combining them with the best bits of the still-popular Windows 7 - including a supercharged version of the iconic Start Menu - and making the whole lot work on every device from smartphone to desktop," he said.
"Microsoft is hoping that having a single platform will encourage developers to create more apps for its mobile phones, something that it's struggled immensely with compared with Android and iOS. It's also making it easier to port iOS and Android apps over to Windows. With the right apps, Windows could finally be a contender in the mobile space - and the wins could be massive."
Millions of PC users will also be able to upgrade for free as Microsoft is making the update available at no extra cost to those who are already using Windows 7 or 8, though this offer will expire next year.
The firm's chief Satya Nadella has said Microsoft wants to move from "people needing Windows, to choosing Windows, to loving Windows".
Users who are not eligible for the free update will have to pay £99 for the Home version of Windows 10, which will go on sale at the end of the month.
Microsoft says there are currently 1.5 billion Windows users worldwide, but the software has come under increasing pressure in recent years from Apple's OS X, which runs on their range of Macintosh desk and laptops, and has seen sales steadily climb while the rest of the market - including Windows - has struggled in the age of mobile devices.
Having also demonstrated how holographic computing can work with Windows 10 via the firm's HoloLens augmented reality headset, Microsoft is hoping to move back to the cutting edge of the technology market with its new release.