When Microsoft's Windows 8 operating system is released Friday, consumers are in for a shock. Windows, used in one form or another for a generation, is getting a completely different look that will force users to learn new ways to get things done.

Microsoft is making a radical break with the past to stay relevant in a world where smartphones and tablets have eroded the three-decade dominance of the personal computer. Windows 8 is supposed to tie together Microsoft's PC, tablet and phone software with one look. But judging by the reactions of some people who have tried the PC version, it's a move that risks confusing and alienating customers.

"There are many things that are hidden," said Raluca Budiu, a user-experience specialist with Nielsen Norman Group. "Once users discover them, they have to remember where they are. People will have to work hard and use this system on a regular basis."

Windows 8 is the biggest revision of Microsoft Corp.'s operating system since it introduced Windows 95 amid great fanfare 17 years ago.

The question is whether the new version, which can be run on tablets and smartphones, along with the traditional PC, can satisfy the needs of personal computer and tablet users.

array of tiles, which can feature updated information from the apps. The "Photos" tile shows an image from the user's collection, and the "People" tile shows images from the user's social-media contacts.

The tiles are big and easy to hit with a finger -- convenient for a touch screen. Applications fill the whole screen by default -- convenient for a tablet screen, which is usually smaller than a PC's. The little buttons that surround Windows 7 applications, for functions like controlling the speaker volume, are hidden, giving a clean, uncluttered view. When you need those little buttons, you can bring them out, but users have to figure out on their own how to do it.

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Not everyone who's tried Windows 8 agrees with critics. Sheldon Skaggs, a Web developer in Charlotte, N.C., said he thought he would hate it, but "after a bit of a learning curve . . . you get used to it" -- and it makes his 5-year-old laptop boot up faster.