Two operating systems stand out in Microsoft's long history as having more than their share of fans: MS-DOS 5 and Windows XP. Released in 1991, MS-DOS 5 was stable, fixed the worst problems of its notoriously buggy predecessor, , and for the first time broke the 640K memory barrier for DOS, allowing memory beyond that to be used for programs, drivers and so-called Terminate and Stay Resident (TSR) programs.

With 2001's Windows XP, Microsoft finally merged its consumer and business lines of Windows, essentially building a consumer-oriented operating system on top of the stable Windows NT kernel. It also finally stopped using DOS as the base operating system, making Windows XP far more stable and reliable than previous versions of Windows.

Some people believe XP was too much of a success, because Microsoft has had a for newer Windows versions. In 2008, signed InfoWorld's "Save XP" petition asking Microsoft to continue support for the aging operating system.

Which is the most beloved? I'll give the nod to Windows XP. MS-DOS 5, as good as it was, ultimately led to a dead end -- it was the best operating system in a line that eventually died out. Windows XP, in contrast, lives on not only on many people's computers, but in the heart of , which still retains its predecessor's merged business and consumer lines.