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What applications? &nbsp;I have a couple of DOS applications whose memory managers are not compatible with any version of Windows. &nbsp;I have to keep a DOS/Windows 3.11 machine around to run them.
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What applications?  I have a couple of DOS applications whose memory managers are not compatible with any version of Windows.  I have to keep a DOS/Windows 3.11 machine around to run them.

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Agreed, Which applications. &nbsp;I also have a couple that connect to com ports for machine controls. dosbox and other dos shells break at the api for the com port. &nbsp;They simply will not work on anything past windows 3.1. &nbsp;
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Agreed, Which applications.  I also have a couple that connect to com ports for machine controls. dosbox and other dos shells break at the api for the com port.  They simply will not work on anything past windows 3.1.  

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I have some old DOS based application which are not running under windows xp and 7. I have enabled compatibility options from properties but still don’t work. I need this application as I still refer those. 
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I have some old DOS based application which are not running under windows xp and 7. I have enabled compatibility options from properties but still don’t work. I need this application as I still refer those. 

Old Dos application doesn't work on the windows vista and windows 7.

Windows 7 is an operating system from Microsoft. Features include multi-touch support, a redesigned Windows Shell with a new taskbar, referred to as the Superbar, a home networking system called HomeGroup, and performance improvements.

Windows 7

Microsoft Windows XP is the sixth release of the NT series of operating systems, and was the first to be marketed in a variety of editions: XP Home and XP Professional, designed for business and power users. The advanced features in XP Professional are generally disabled in Home Edition, but are there and can be activated. There were two 64-bit editions, an embedded edition and a tablet edition.

Windows XP

Windows Vista is an operating system created by Microsoft as the successor to Windows XP. It was intended for PCs, workstations and laptops, and shares the same code base as its successor, Windows 7. New features included an updated graphical user interface (GUI) and visual style dubbed Aero, a new search component called Windows Search, redesigned networking, audio, print and display subsystems, and new multimedia tools. Vista aimed to increase the level of communication between machines on a home network, using peer-to-peer technology to simplify sharing files and media between computers and devices. Windows Vista included version 3.0 of the .NET Framework, allowing software developers to write applications without traditional Windows APIs.