The vast majority of existing touchscreen PCs can be used with Windows 8, according to Microsoft, but tablets and PCs designed to meet its new guidelines will offer a better user experience for touch applications going forwards.
In an update to the Building Windows 8 blog, Microsoft reiterated that Windows 8 hardware should support a minimum of five fingers for multi-touch input.
However, the basic gestures used to interact with Microsoft's upcoming platform require no more than two fingers, and so the vast majority of Windows 7 touchscreens will be compatible, the company said.
"if you have a Windows 7 touch-capable PC today, don't hesitate to use the Windows 8 Consumer Preview and take advantage of the Metro-style user experience that we've built," wrote test manager, Jeff Piira and group programme manager, Jerry Koh.
But Microsoft had to work closely with partners to make this work, according to the firm, because there is some variation in performance between touchscreens on Windows 7 systems.
For example, Microsoft had to make gestures such as press and hold more forgiving because lack of precision can make it hard to define whether a finger touching the screen is stationary or moving.
Microsoft lists a number of machines that are known to work with Windows 8, although the firm said this should not be taken as an endorsement and users should not expect official support from the vendors when installing and testing Windows 8.
The systems Microsoft itself uses for Windows 8 are:
HP Elitebook 2760p convertible
ASUS EP121 tablet
Dell Inspiron Duo convertible
Lenovo x220t convertible
3M M2256PW 22" display
Samsung Series 7 slate
The Windows 8 "touch language" defines eight basic gestures, including slide to pan, swipe from the bottom edge for app commands and from the side edge for system commands, as well as tapping to initiate an action and pinching to zoom.
While these require no more than two fingers, "it is important to note that two fingers can be very limiting for a variety of applications," said Piira and Koh.
Microsoft specified a minimum of five fingers in response to feedback from developers who indicated they may require more touch points for future applications.
As an example, Microsoft showed at its Build conference last year how users could move an application tile by picking it up and holding it with one finger, while using the other hand to pan the screen horizontally by swiping.
Microsoft said it will ensure consistency and quality in touch hardware for Windows 8 by testing and certifying each new touch device before it can enter the market. However, it has yet to detail the certification process.
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