The company is holding a press conference on Thursday in New York, at which the firm will discuss more details on the operating system that its chief executive Steve Ballmer openly admits he is 'betting the company' on.
Retailers around the world will tomorrow start selling desktop PCs, laptops, tablets and hybrid devices with Windows 8 installed, while PC users with compatible machines can upgrade their kit to the software.
Alongside the unveiling of the touch-enabled software for PC devices, Microsoft has today started shipping Surface - its first major foray into hardware with a line of table computers that will compete with Apple's iPad.
Microsoft hopes to fend off renewed competition from Apple's Mac by offering a touch-based, dynamic operating system that can run on processors designed for high-spec machines and chips that usually run on mobile devices.
The new operating system borrows heavily from Microsoft Windows Phone software, including the use of 'live tiles'; squares laid out in different sizes on a loose grid that denote each different app or programme.
These 'tiles' launch the applications, but also show updates in real-time, such as the Skype for Windows 8 app alerting the user when they have a missed call. Users can also switch to the traditional Windows desktop view if they so wish.
Windows 8 is such an important launch for Microsoft as its position as market leader in computer software is under threat. Gartner estimates that more than 1.5 billion devices currently use a version of Windows, making it the most installed operating system ever.
However, investors are concerned that Microsoft has not moved fast enough to address the shift in consumer behaviour towards touchscreen, particularly tablet computer devices.
"We think the industry changed with the iPad launch because the tablet is effectively a PC - it doesn't need to be connected to a network to work and runs third-party applications," Steve Brazier, chief executive of research firm Canalys, told the BBC.
"Once you segment the market that way, Windows share of the global PC market has fallen to 72%. Three years ago that would have been over 95%.
"If you add the PC market together to the smartphone market - which we call the intelligent device sector - Windows share falls to 32%."
A range of tablets running a version of Windows 8 will launch from various different manufacturers tomorrow, such as Samsung and Toshiba, but they will have to compete with Microsoft's own Surface products.
The premium tablet line has a HD screen measuring 10.6 inches on the diagonal, and packs up to 64GB of internal storage. The £399 entry-level version (using an ARM CPU and running Windows RT) has already sold out in the UK, despite getting a mixed response from the critics.
Reviews have praised the hardware of the debut Windows RT tablet, but have criticised the fact that users can only install third-party software from Microsoft's own Windows Store, where choices are much more limited than Google Android or Apple's iOS.
Microsoft has also been criticised on a more general level over the perception that it has created a 'walled garden' around the operating system. Critics have said that the new Windows 8 risks the free and openness of previous Windows generations.
By imposing a user interface and adding apps in the Windows Store, Microsoft is putting itself as the gatekeeper (a model often favoured by rival Apple) and so dictating what is and is not given prominence to users.
Gabe Newell, the co-founder of Valve, said in July that Windows 8 was a "catastrophe" for the PC ecosystem due to its closed platform
"In order for innovation to happen, a bunch of things that aren't happening on closed platforms need to occur," Newell said.
"Valve wouldn't exist today without the PC, or Epic, or Zynga, or Google. They all wouldn't have existed without the openness of the platform.
"There's a strong temptation to close the platform, because they look at what they can accomplish when they limit the competitors' access to the platform, and they say 'That's really exciting'."
Another key challenge facing Microsoft is customer education, as the Windows 8 software comes in two flavours based on individual chipsets for the first time.
Windows 8 is the official product name for the software on PCs running x86 processors - 32bit and 64bit. There will be just two versions offered, Windows 8 and Windows 8 Pro, rather than the previous system of Home Basic, Premium, Pro, Ultimate versions for Windows 7.
For ARM-based tablets and PCs, which generally pack more battery life but lower processing power and are often referred to by Microsoft as Windows on ARM (WOA), there will be a different version of the operating system, known as Windows RT.
This is the first version of Windows to run on different chipsets, and Forrester senior analyst Sarah Rotman Epps feels that there is a risk of confusing consumers with the approach.
"Most consumers don't pay attention to the chipset in their device, but Microsoft's latest update to its Windows operating system forces buyers to confront the trade-offs of chipset choices," she said. "It gets confusing quickly."