The name is a surprise bearing in mind it represents a jump from the last version – Windows 8.
The software will run on a wide range of devices from smartphones and tablets to PCs and Xbox games consoles, with applications sold from a single store.
It also marks the return of the Start Menu, which had been removed from Windows 8.
In addition to offering a list of the user’s favourite applications, the menu also brings up resizable tiles – similar to those featured in Windows 8’s touch-centric interface – on PCs and tablets.
These provide a quick view of notifications from relevant applications, such as details of new emails, Facebook messages and weather forecast updates.
The company said the facility was intended to make the software seem familiar to both users of Windows 8 and Windows 7.
The behaviour of the OS will depend on the type of device it is being used on. Unlike its predecessor, users will not need to switch between Desktop Mode and the touch-focused alternative.
However, they can still spread a number of “live tiles” across the screens of two-in-one laptop-tablet hybrids to make them easier to use with both a mouse and finger presses.
Windows 8 had been criticised for being too different to the previous version, which deterred some organisations from introducing it.
It initially lacked a Start button altogether, and when one was introduced it only switched to the touch-centric tiled interface or – if a long mouse press was used – provided access to the system’s control panel and other functions.
Businesses typically wait about a year after a new operating system’s release before offering it to workers to give IT staff a chance to get to grips with the new technologies involved.
But it has been nearly two years since Windows 8 first went on sale and adoption is still low.
“It’s extremely important for Microsoft to get Windows 10 right,” said David Johnson, who covers Microsoft for the consultancy Forrester.
“Windows 8 is only being offered to employees by about one in five organisations right now. Windows 7 is still the de facto standard for enterprise in the desktop environment.
“For Microsoft to continue to be able to get the best and latest technology in the hands of the enterprise workforce all over the world, it has to have a vehicle to do that – and Windows 9 is its best shot.”