Most software designed for Windows requires a version of Microsoft’s .NET framework software to run.
.NET Framework – http://en.wikipedia.org/wiki/.NET_Framework
“Programmers produce software by combining their own source code with .NET Framework and other libraries.”
Windows 8.1 supports only .NET version 3.5 and higher versions, therefore any software that requires a lower version won’t be able to run. The soon-to-be-released Windows 10 (there is no version 9) also won’t support versions lower than 3.5. Software that requires a version of the .NET framework usually installs the one that it requires during its installation. Several versions can be installed. Installing one version does not overwrite any existing versions. Previous versions are not removed when the latest version is installed. All of the installed versions can be uninstalled.
Note that some software, Quicken and QuickBooks, for example won’t install unless they recognise the version of Windows being used. Quicken 2000, for example, will only install on a Windows 2000 or Windows XP system. In that case you won’t ever be able to get such software to install and run in a later version of Windows (Vista/Windows 7/Windows 8.1).
Windows 8.1 has an application-compatibility tool that could allow installed software to run that doesn’t have to recognise the version of Windows. To use the tool, right-click on the application’s icon or its executable .exe file, click Properties in the menu that presents itself. Open the Compatibility tab in the window that appears. There is a box beside which “Run this program in compatibility mode for:” appears. The drop-down menu provides versions of Windows that the software can be made compatible with by choosing its option from Windows 7 to XP or even as far back as Windows 95. The “Run this program as an administrator” option should also be enabled. If the software works properly, the problem is solved, but if it requires an earlier version of the .NET framework than the lowest version that Windows 8.1 supports, it won’t run.
The Professional and Ultimate versions of Windows 7 provide a Windows XP mode that software designed for Windows XP can be installed in and run as if it were running in XP itself. Unfortunately, Windows 8.1 does not provide a mode that runs earlier versions of Windows. However, it is possible to run a virtual machine in Windows 8.1 within which an earlier version of Windows can be installed and run. Microsoft’s free Hyper V virtual-machine technology can be used.
Run virtual machines on Windows 8.1 with Client Hyper-V –
Alternatively, a third party virtual machine, such as VirtualBox can be used, which Oracle provides free of charge.
VirtualBox.org – https://www.virtualbox.org/
Note that OEM versions of Windows cannot be run from within a virtual machine because they can only be installed on a single system. A version with a full retail licence is required, an Upgrade retail version can’t be used because its use requires the detection of an earlier qualifying version of Windows.
An OEM version of Windows is installed in a computer by a system builder, which could be a brand-name company or an individual who has purchased an OEM version, usually for a self-built PC. An OEM version can only be installed on the computer it came installed on or was installed on by the system builder. A retail version can be installed on unlimited PCs as long as only one of them is in use at any particular time. The letters OEM appear in the Product Key that is used to activate the copy.
As a last resort, you could just keep a computer with the earlier version of Windows installed on it just to run particular old software that won’t run on later versions of Windows. If you want to build such a computer, suitable motherboards, processors and RAM memory, often as bundles with that come with their driver discs are available on eBay inexpensively.