Windows 10, the biggest update Microsoft has ever made to its computer software, is set to launch tonight.
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.
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".
Windows users who have registered their interest will be notified once Windows 10 becomes available to them, with the roll out beginning in the early hours of Wednesday morning, and set to be staggered over the coming days.
Those 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.