Virtual PC of
    Microsoft bought and developed Virtual PC for Windows. This allows one to make a MS-DOS machine on the latest blazingly-fast personal computers. See for documentation, including Virtual PC 2004 and Virtual PC 2007.
    Linked are Virtual PC 2004 and Virtual PC 2007. One also needs VM Additions for DOS. I prefer Virtual PC 2004. Also linked are floppy drive images of MS-DOS 6.22 and MS-DOS 7.10. I prefer DOS 6.22 for the Defrag.exe utility program.
    The last zip file is named It contains two files. One is a blank virtual floppy disk "blank.vfd" and the other is "himem395.sys". DOS 6.22's himem.sys is version 3.10 and DOS 7.10's himem.sys is version 3.95.
    When running DOS 6.22 and using extended memory manager, himem.sys v3.10, I ran mem/p and the total extended memory is limited to 65,535 Kb or 64 Mb. Only changing himem.sys to version 3.95 and running mem/p the total extended memory is 261,056 Kb or 255 Mb (in my case). This is why I use DOS 6.22 but with himem.sys version 3.95 from DOS 7.10.
    From Wikipedia - "eXtended Memory Specification (XMS)

    "The eXtended Memory Specification or XMS is the specification describing the use of IBM PC extended memory in real mode for storing data (but not for running executable code in it). Memory is made available by extended memory manager (XMM) software such as HIMEM.SYS. The XMM functions are accessible through interrupt 2Fh.

    "XMS version 2.0 allow for up to 64 MiB of memory, with XMS version 3.0 this increased to 4 GiB. To differentiate between the possibly different amount of memory that might be available to applications, depending on which version of the specification they were developed to, the latter may be referred to as super extended memory or SXMS.

    "The extended memory manager is also responsible for managing allocations in the high memory area and the upper memory blocks. In practice the upper memory blocks will be provided by the expanded memory manager, after which DOS will try to allocate them all and manage them itself."