"Beginning today, consumers with a Windows 8 device can download free update via online Windows Store. Over the next few weeks and months, Windows 8.1 will also be available on new devices at retail locations," Microsoft India said in a release.
The new OS marks a wave of new, innovative devices coming for consumers and businesses from the convenience and mobility of tablets and 2-in-1s to the productive experience expected from laptops and all-in-ones, it added.
Many of these new devices are touch-enabled and will deliver advancements in processing power, battery life and design, across a range of price points, Microsoft said.
The company claims that Windows 8.1, released within a year of the launch of Windows 8, provides a more customisable start screen with variable tile sizes, more background designs and colours so that each Windows device will look completely unique and personal to the individual.
The features also include a built-in Bing search, smart SkyDrive syncing and visual changes to the Start Screen and application snapping.
Windows 8.1 also brings back Start button as a familiar point of navigation. An All Apps view lets users see all of their apps at once for easy access and new clicks and cues as well as a Help and Tips app that get you up to speed quickly.
Experts and users had criticised Microsoft of doing away the Start button.
Facing stiff competition from Apple's iMac and Mac Book as well as tablets eating into PCs share, Microsoft, which once ruled the desktop and laptop markets, launched Windows 8 last year.
The release of its latest OS also assumes importance in the backdrop of Microsoft's shift to devices and services versus packaged software.