And I advise would-be upgraders who aren't enthusiasts to wait to upgrade at least for a few months, until the product is more stable and reliable.
Microsoft says that Windows will now be treated as a "service," with frequent small updates to quash bugs and add features. So this may be the last release of Windows with a formal new name.
Easing the Confusion
Windows 8 confusingly jammed two different interfaces, with two different types of apps and two different optimal input methods (touch and mouse) into the same OS. It eliminated the Start menu and booted instead into a Start Screen with tablet-style apps represented by tiles. The standard desktop, and its standard apps, were demoted.
In Windows 10, PCs boot into desktop mode. The tiled tablet look has been demoted to a section of the restored Start Menu. Or you can decide to switch to Tablet Mode, where it will dominate. But it's your call.
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What's more, the tablet-style apps run inside windows in the desktop mode, just like traditional Windows programs. A new type of "universal" app will supposedly be able to run, in the appropriate mode, on all forms of computers — traditional desktops and laptops, hybrid laptop-tablets, pure tablets and even, later this year, Windows phones.
Cost and Strategy
Microsoft is giving away Windows 10 as a free upgrade to users of the latest revisions of Windows 7 and Windows 8. The free offer lasts up to a year from today, but it won't be immediately available to all. It will begin with beta testers (so-called "Windows Insiders") and then spread to people who have reserved copies; then, on to others. A prompt will pop up on PCs that are eligible to upgrade.
The hardware specs for running Windows 10 are identical to those for Windows 7, but it still may not work well on older machines with slower processors and other limitations. The installation app will check for compatibility.
Still, Microsoft hopes that hundreds of millions of people will upgrade. That's a reversal of its longtime strategy, in which it paid little attention to upgrades, and saw new versions of Windows as mainly a way to sell new PCs.
The reason? The company hopes that if it can get enough PCs on Windows 10, developers will be incentivized to write the new universal apps. And, since these will also run on Windows Phone, it will help revive that failed mobile platform, which has struggled to attract popular apps.
If you don't, or can't, do a free upgrade, you can buy a new PC, or Microsoft will sell Windows 10 starting at $119.
What's Old Is New
In some ways, the biggest new feature is an old one — the return of the Start menu. As in the past, it's on the lower left of the screen and lets you launch apps and settings easily, and shut down the PC. But now it includes a mini version of the Windows 8 tiled Start Screen, which you can expand.
This menu lists your most-used apps, those you've chosen to pin to the menu (as tiles) and even all apps, if you care to see them. Settings have been simplified and enhanced but — confusingly — for some things, you still have to use the ancient Control Panel, which is still there. Microsoft says it's working to eventually get rid of the Control Panel, but not soon.
Listen to Me (Some of the Time)
The most notable brand-new feature is Cortana, the combo search box and intelligent assistant. By typing in a box labeled "Ask Me Anything" at the lower left of the screen or speaking a question using a microphone icon, you can look for files, launch programs, play songs, get information from the Web and more.
For instance, in my tests, it could tell me the weather, or how my calendar looked, or how many people live in Kansas. It could find various documents by searching for words within them, and set reminders. You can even opt to have it listen for a trigger phrase ("Hey, Cortana") and just speak questions or commands to it without tapping or clicking on the microphone icon.