NEW YORK On Friday, Microsoft Corp. released a new version of its Windows operating system, one designed to bring the desktop and laptop experience to tablet computers.

There are several ways to get it – or avoid it.

Windows 8 represents the software company’s effort to address the growing popularity of smartphones and tablet computers, namely the iPad.

The new software is a radical departure from previous versions of Windows. It may take people time to get used to the changes. The familiar start menu in the lower left corner is gone, and people will have to swipe the edges of the screen to access various settings. The new screen is filled with a colorful array of tiles, each leading to a different application, task or collection of files.

Windows 8 is designed especially for touch screens, though it will work with the mouse and keyboard shortcuts, too.

There are several versions of Windows 8:

•  Windows 8. Like its predecessors, Windows 8 will run on computers with processing chips made by Intel Corp. or Advanced Micro Devices Inc. The basic version is designed for consumers, and a Pro version is for more tech-savvy users and businesses. The Pro version has such features as encryption and group account management.

Large companies with volume-licensing deals with Microsoft will want Windows 8 Enterprise, which has additional tools for information-technology staff to manage machines.

•  Windows RT. For the first time, there’s also a version that runs on the lower-energy chips that are common in phones and tablets. That version will run on tablets and some devices that marry tablet and PC features.

While tablets with Windows 8 can run standard Windows programs, the RT devices will be restricted to applications specifically designed for the RT system.

Borrowing from Apple’s playbook, Microsoft is allowing RT to get applications only from its online store, and apps must meet content and other guidelines.

•  Windows Phone 8. The phone version won’t be available until an unspecified date this fall. Microsoft has an event about it Monday and may announce more details then. Nokia Corp. and Samsung Electronics Co. already have announced plans for new Windows phones.

You can get Windows RT and Windows Phone 8 only by buying devices with the software already installed. Windows 8 can be purchased as an upgrade as well.

How to get or avoid it

Here’s how you can get – or avoid getting – Windows 8:

•  Buy a new machine. Desktop, laptop and tablet computers with Windows 8 already installed went on sale Friday around the world.

Windows chief Steven Sinofsky said 1,000 PCs have been certified for Windows 8. The cheapest cost about $300.

Several PC manufacturers, including Samsung, Lenovo Group Ltd., Hewlett-Packard Co. and Dell Inc., have designed new Windows 8 machines.

Many of the devices are available now, though some models won’t go on sale for another month or two.

Meanwhile, retailers such as Best Buy Co. have trained staff members to explain and demonstrate the new system.

Microsoft also started selling its Surface tablet with Windows RT on Friday, but it’s available only at its retail stores and on its website. A Windows 8 version for the Surface tablet will come out later.

•  Upgrade your machine. Anyone who has purchased a Windows 7 PC (other than the Starter Edition) since June 2 can buy Windows 8 Pro for $14.99. The offer applies to Windows 7 PCs sold until Jan. 31, and the upgrade must be claimed by Feb. 28.

To claim the offer, register the machine at https://windowsupgradeoffer.com. You’ll get an email with a promo code, which you can use to get the Windows 8 upgrade online.

If you bought a Windows PC before June 2, you can upgrade for $39.99. You must already have Windows XP with Service Pack 3, Windows Vista or Windows 7.

Those who prefer to buy a DVD to upgrade will have to pay $69.99.

Before buying the upgrade, check to make sure your machine is strong enough to run Windows 8. Microsoft lists the system requirements here: http://windowsupgradeoffer.com/en-US/Home/ProgramInfo.

Not sure whether you have what it takes? Microsoft has an upgrade tool that will stop you if you try to buy Windows 8 without the requirements. The tool also will warn you of software that may need updates to work on Windows 8. Go to http://windows.com to get started.

If you’re upgrading from Windows 7, the tool will let you keep settings, personal files and applications. From Vista you can migrate settings and files; from XP, only files. You’ll also have the option to start fresh and bring nothing to Windows 8.

•  Keep older versions of Windows. If you do not wish to upgrade to Windows 8, do nothing.

Most machines now on sale will have the new version of Windows, though it’s still possible to buy Windows 7 machines or upgrade to Windows 7. You may have to order online, and your choices may be restricted to gaming or business-oriented machines.

Microsoft hasn’t said what the cutoff date for Windows 7 will be, but expect to be able to buy Windows 7 as an upgrade for another year or preinstalled on a new machine for two more years.

After Windows 7 came out in October 2009, for instance, retailers were still allowed to sell boxed versions of the predecessor, Vista, until October 2010. PC makers were able to sell Vista machines until October 2011.

Microsoft plans to continue providing technical support for Windows 7 until Jan. 14, 2020.