When you buy a copy of Windows 7 to install on an existing computer, there are three key questions you need to ask yourself:

  • Which edition of 7 do I want?
  • Can I buy an upgrade version or do I need to pay for the more expensive full version?
  • Should I choose a 32-bit or 64-bit version?

Which edition?

Windows 7 comes in six editions, but unless you work in a large company or live in what’s called an “emerging market” such as Bangladesh or China, there are only three editions that matter: Home Premium, Professional and Ultimate.

Use the Windows Compatibility Center site to check whether your favorite applications and hardware are compatible with Windows 7.

There are three key differences between Home Premium and Professional. Professional lets you back up your system to a network device; it provides support for XP Mode; and it allows you to connect to a company’s networking domain. The Ultimate edition includes those three advanced features plus BitLocker file encryption and the ability to run multi-lingual Windows.

Home Premium is almost certainly the edition you’ll want for your home computer, and many small businesses will be happy with Home Premium, too. Backing up across a network is probably the most appealing option omitted from Home Premium, but for most people its absence won’t be a deal breaker. If you need to run old XP applications which are not compatible with Windows 7, the XP Mode feature supported by the Professional and Ultimate editions will give you that capability, but be aware that your computer will need a BIOS (basic input/output system) with support for hardware virtualization in order to run XP Mode. Hardware virtualization has been available in PCs for several years, but whether your particular processor supports it is a hit-and-miss affair. Before paying extra for the Professional or Ultimate versions of Windows 7, check that your computer can support XP Mode by reading through the documentation provided online, in particular the ‘Requirements’ and ‘Configure BIOS’ sections. To use XP Mode, you’ll first need to download it, together with Windows Virtual PC (it’s free).

By the way, there’s also a Starter edition of Windows 7, but it’s not available over the counter. You may, however, encounter it pre-installed on some netbooks at the cheaper end of the market.

Hardware requirements

Windows 7 is remarkably undemanding when it comes to hardware. The 32-bit version will run on a computer with:

  • 1 gigabyte (GB) of RAM
  • 1 gigahertz (GHz) processor
  • 16GB of free space on the hard disk
  • DirectX 9 graphics with WDDM 1.0 or later.

If you want to run the 64-bit version you’ll need an additional gigabyte of RAM and 4GB more hard disk space.

Those are the minimum specifications recommended by Microsoft. If you’re buying a new computer with Windows 7 pre-installed, unless it’s a netbook don’t settle for anything less than a 2GHz processor, 3GB RAM (4GB on a 64-bit system) and a good sized hard drive—say 160GB or more.

Upgrade versus full licenses

If you already own Windows XP or Windows Vista, you qualify to buy an ‘upgrade’ version of Windows 7. The upgrade license is considerably less expensive than the full license.

If you buy an upgrade version and your computer is currently running XP, you won’t be able to perform what’s called an in-place installation. In-place installation lets you preserve your existing data and programs during the installation process, but it’s available only to those upgrading from Vista. If you are using XP, you’ll have to perform a custom (‘clean’) installation. That is, you’ll need to back up all your data, perform the setup routine, then copy your data back onto the computer, reinstall all your applications and adjust their settings.

This sounds like a big deal but, in fact, there are good reasons to perform a clean installation instead of the faster in-place upgrade no matter whether you’re upgrading from XP or Vista, because it prevents your brand new operating system from inheriting any problems your existing system may have.

Don’t confuse upgrade and in-place

Quite a few XP users end up buying the more expensive full Windows license even though they qualify for the cheaper upgrade license. That’s because of Microsoft’s confusing terminology: they read that it’s not possible to do an “in-place upgrade” from XP to 7 and think that means they don’t qualify for the upgrade license. Not so! If you’re running Windows XP, you qualify for the cheaper upgrade license.

Refer to Table 1 to see whether your current version of Windows can be upgraded using an in-place upgrade or whether you’ll need to perform a custom installation.

32 or 64 bits?

Most of the personal computers built since the ’80s have been built around 32-bit microprocessors. These processors handle data in 32-bit chunks and can refer to 2^32 memory addresses (that’s 4 gigabytes of RAM). In the past few years, 64-bit desktop computers have become increasingly common. These newer machines are able to deal with 64-bits of data at once and can, in theory, work with an absurd amount of RAM. So absurd, in fact—we’re talking 17.2 billion gigabytes of RAM—that most 64-bit computers are artificially limited to a tiny fraction of that amount.

In practical terms, a 64-bit desktop will outperform a 32-bit machine when it comes to running multiple programs simultaneously. If you’re an extreme gamer or spend a lot of time editing video, 64 bits is the way to go.

To make the most of that potent hardware, though, you need an operating system and applications written to take advantage of the power, and you need 64-bit drivers to run any peripheral devices—printers, scanners and the like—you have attached to the computer. The recent surge in popularity of 64-bit machines has been helped along by the existence of 64-bit versions of Windows and increasingly available 64-bit drivers. We’re still waiting to see a good selection of 64-bit applications.

Windows 7 comes in both 32-bit and 64-bit flavors. You can run the 32-bit version of the operating system on a 64-bit computer, but you cannot run the 64-bit operating system on a 32-bit computer.

So, if you buy a 64-bit computer, should you get the 64-bit version of Windows 7? Not necessarily. If you still use old programs or old hardware, 64-bit Windows may cause you problems. There are also some fairly recent programs that don’t work on 64-bit Windows. The number of such programs is rapidly dwindling, but if you’re concerned about compatibility, you should opt for 32-bit Windows 7. On the other hand, if you want the very best performance from your equipment and you can get 64-bit drivers for all your hardware, then by all means opt for the 64-bit version.

Is my computer 64-bit?

How can you tell if your computer can run a 64-bit version of Windows? To do so, it must have a 64-bit-capable processor. To check whether yours qualifies, if you’re currently running Vista:

  1. Click Start -> Control Panel, type performance information and tools in the search box, and click Performance Information and Tools in the list of results.
  2. Click ‘View and print details’.
  3. In the System section, if you’re running a 64-bit version of Vista you’ll see that listed beside ‘System type’. If you can run 64-bit Vista, you can run 64-bit Windows 7. If you’re not currently running a 64-bit version of Windows, note the ‘64-bit capable’ setting, which will tell you whether your processor is able to run a 64-bit system.

If you’re currently running Windows XP:

  1. Click Start, right-click My Computer and select Properties from the context menu.
  2. If your processor is capable of running a 64-bit operating system you’ll see “x64 Edition” listed in the System section. Even if you don’t see “x64 Edition”, your XP computer might still be capable of running a 64-bit operating system. To double check, run the Windows 7 Upgrade Advisor. It’s a free download.

Windows anytime upgrade

Microsoft has made it easy for those of us who can’t make up our minds which version of Windows we want with a feature called Windows Anytime Upgrade. The Windows 7 installation DVD contains all the different editions of Windows 7, although you’ll only be able to install the one for which you’ve purchased a license. But should you buy, for example, Windows 7 Home Premium and then subsequently decide you want the features of Windows 7 Ultimate, you’ll be able to purchase an upgrade license and use the newly supplied product key to “unlock” the version you already have on hand and upgrade your PC. Note that you cannot upgrade a 32-bit version of Windows to a 64-bit version.

To buy an upgrade key, click Start, type anytime upgrade in the search box, and click Windows Anytime Upgrade in the results list and follow the instructions.

Is my software compatible?

Before you upgrade to Windows 7, check whether your existing must-have applications and hardware are compatible with the new operating system by visiting the Windows Compatibility Center.