What are DOS Programs
What are 16-bit applications (DOS programs)?
16-bit application is a modern term used by Windows to describe legacy DOS programs. 64-bit editions of Windows cannot run 16-bit applications, while 32-bit editions offer partial support.
DOS is the name given to the original type of operating system used on early Intel x86 compatible personal computers. Similar to how the generic term Windows is today used to describe the modern Microsoft based operating systems. All 32-bit Intel and AMD CPU's are backwardly compatible with this DOS legacy. If you were able to find an old floppy drive for your current 32-bit PC you could probably successfully boot your PC into a version of this ancient operating system.
DOS based operating systems came in a number of different variants which were promoted by different companies. The most well known of these DOS systems and the benchmark for what most software companies would target development towards was Microsoft's MS-DOS.
Interesting enough DOS itself was originally a quick clone of the earlier, popular 8-bit operating system known as CP/M. This was a system that was first released by Digital Research back in 1974. Seattle Computer Products a small unknown company created the original PC-DOS, known as Q-DOS in 1980. Q-DOS had similar but a less extensive range of functions to CP/M but used the Microsoft QBasic FAT file system.
Microsoft had a contract with IBM to supply the operating system to a secret project which became the first IBM PC. Microsoft bought a non-exclusive licence to market Q-DOS and hired its author to port the system to the Intel 8088 CPU that IBM was planning to use. This version of DOS was known as 86-DOS. In April 1981 Microsoft bought all the rights to DOS and changed the operating system name to MS-DOS. IBM released the first public version of DOS, PC-DOS 1.0. This was integrated into the first IBM Personal Computer, the IBM 5150 PC.
DOS was the de-facto operating system for all Intel x86 compatible personal computers up until 1995. After which the popularisation of Microsoft's Windows 95 eventuated which slowly lead to the abandonment of DOS. Even then though, this and subsequent versions of Windows including 98 and ME all used DOS as their underline base. This is important to know though as up until Windows XP in 2001, many applications programmed by individuals of scene were still developed for DOS.