Microsoft is still licking the wounds from the beating it took over Windows Vista's application and hardware compatibility.
Consequently, right from the very first official unveiling of Windows 7, the company has been at pains to stress the measures it's taking to ensure existing software and devices will work from the get-go.
One small but significant measure it's already deployed is to leave the version number of the OS almost unchanged. This might be Windows 7, but as far as software is concerned, it will be known as Windows 6.1.
Why? Because many applications and drivers are set to check the version number of software before installation to ensure they're not installed on incompatible OSes.
As Vista and Windows 7 share the same core code, Microsoft has decided to merely nudge up the version number (Windows Vista was 6) so that applications are tricked into thinking it's Vista they're dealing with.
That sleight of hand will help ensure that the overwhelming majority of commercial software written in the past two or three years will work seamlessly with Windows 7. But what about those bespoke, legacy apps that many businesses rely on?
The rabbit Microsoft pulled from the hat for the launch of the Release Candidate is Windows XP Mode. This downloadable add-on provides a virtual version of Windows XP SP3 for Windows 7, allowing companies to install legacy apps but run them as if they were native Windows 7 software.
The download comes in two parts: Microsoft's Virtual PC software - which manages the virtual machines in Windows 7 - and Windows XP Mode itself, which is essentially a fully licensed version of Windows XP SP3. Once installed, you simply select Virtual Windows XP from the Start menu, install your legacy app as you would normally on XP, and it's ready to go.
The clever part is that the legacy application can then be accessed straight from the Windows 7 Start menu or even pinned to the new taskbar. After installation, the virtual OS becomes practically invisible, as the application opens in its own window, just like a native app would. It's incredibly slick.
There are a couple of drawbacks, however. Although the virtualised legacy apps behave like any other Windows 7 program, they can take a couple of minutes to get going, as Windows boots the virtual XP OS in the background.
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| XP Mode is only allocated 256MB of RAM by default, but that can be boosted in the virtual memory settings |
Performance isn't as snappy as running the apps on a normal XP desktop either. Note that the virtual Windows XP OS is allocated only 256MB of RAM by default - we found boosting that up to 1GB in the Virtual Machine settings menu gave performance a massive lift.
There are also reasonably stringent hardware requirements to run XP Mode. Aside from a minimum of 2GB of RAM, the PC's processor must have virtualisation support (either Intel VT or AMD-V), which has to be enabled in the BIOS before installation.
That rules out a number of mainstream processors from both Intel and AMD, including members of the Core 2 Duo family and AMD's Sempron processors. You'll want to check compatibility before upgrading to Windows 7 or buying a new PC.
Nevertheless, XP Mode does provide an elegant safety net for firms that want to take advantage of Windows 7, but are clinging to XP for business-critical apps.
Bigger firms operating a Windows Server 2008 environment already have an application virtualisation offering - MED-V - which offers features such as centralised deployment and management that XP Mode doesn't.
Also in our series, Windows 7 the complete guide:
Part 4: Playing DivX and XviD files
Part 3: Will your PC actually boot any quicker?
Part 2: Raw performance benchmarks
Part 1: Good news for gamers?
Also see: The 30 Best Features of Windows 7