Chow said the estimate, based on data from technology research firm IDC, specifically covered consumer devices in Hong Kong which run on qualified and genuine Windows 7, Windows 8 and Windows 8.1 operating systems.

He pointed out that the year-long Windows 10 initiative in Hong Kong will be supported by more than 20 original equipment manufacturers, including China's Lenovo Group, United States-based Dell and South Korea's Samsung Electronics.

Those hardware partners of Microsoft are expected to release more than 100 new devices on Windows 10 over that period. 

The city's big consumer electronics chains, led by Fortress and Broadway, form part of more than 400 local retail outlets that are now selling Windows 10-based devices. 

Gartner analyst Stephen Kleynhans said in a report that much of the initial marketing of Windows 10 will likely focus on consumer-friendly features, such as integration with the Xbox One video game console and Microsoft's Cortana virtual personal assistant -- a rival to Apple's Siri.

"However, senior IT managers, planners and even CIOs will find there is a lot they need to understand about the operating system as they begin planning end-user computing environments for the next three to five years," Kleynhans said.

Chow pointed out that it was the hope of all industry participants that Windows 10 could help perk up device sales, particularly of personal computers, in the city.

He said about 60 per cent of Microsoft's enterprise customers have been testing Windows 10, which could augur well for future sales in this segment where no free upgrades are given.

"The development of Windows 10 was helped by the feedback from more than five million early adopters from around the world, including a sizable number from Hong Kong," he said.

The Windows 10 campaign from Microsoft and its partners could even give a boost to the overall information technology market in Hong Kong.

Research firm Gartner has forecast the city's total spending on information technology this year to rise 13.6 per cent to HK$231.2 billion (US$29.83 billion), up from HK$203.5 billion last year. 

This total market includes devices, software, communications services, data centre equipment and information technology services.

The largest spending category in Hong Kong is devices, worth an estimated HK$129.7 billion this year. This includes PCs, smartphones, tablets and printers.

In a report, Forrester Research said Microsoft aims to have one billion devices running Windows 10 within two to three years. 

Watch: Reaction to Microsoft's Windows 10 launch

The free consumer upgrades for devices on Windows 7, Windows 8 and Windows 8.1 are supposed to help drive mainstream interest. 

"Creating scale would allow Microsoft to establish Windows 10 alongside iOS and Android as a must-target platform for developers," the Forrester report said.

Having a common platform would support and enable a range of consistent and familiar capabilities for users, developers, and information technology management teams across the growing variety of “smart” , or digitally connected, products. These include Microsoft's Xbox One console and HoloLens head-mounted virtual reality display.

Forrester expected enterprises to gradually embrace Windows 10 over the next few years.