MS-DOS was
Microsoft's initial offering in the
IBM PC
operating system arena. At the time Microsoft forged the deal with IBM to supply the OS, MS did not have an operating system to sell them. Instead, they purchased an OS called
QDOS (Quick and Dirty Operating System) from Tim Paterson of Seattle Computer Products for $50,000. IBM agreed to let Microsoft retain the rights to their operating system, and this agreement is what most see as the foundation upon which Microsoft was able to build its empire. MS-DOS continued as a standalone operating system up through version 6.22. DOS with version numbers of 7.0 and beyond were included with the Windows 9x/ME series of operating systems. From
Windows 95, one could
boot into DOS by pressing F5 during the "Starting Windows 95..." message and selecting "Command Prompt Only". In Windows 98, one must hold down the Ctrl key immediately before the
Windows logo shows up. Although
Windows ME is still based on DOS, Microsoft elected to remove the
command line as a startup option. However, ME still allows you to create a startup disk that boots into DOS mode.
Today DOS is generally considered to be an outdated operating system. However, it still has many uses. It is small and boots very quickly, making it useful in embedded systems. It is small enough and simple enough that one person can conceivably gain a detailed perspective of how the operating system works as a whole. One thing that really sets DOS apart from most modern OSes is that programs can directly access the hardware. Although this flies against what is considered "good practice" in programming, it allows a programmer to very easily access the hardware at the lowest level. Additionally, the DJGPP compiler gives programmers the ability to write 32-bit protected mode programs without worrying about segment:offset addressing or small/medium/large memory models or any such complexities normally associated with 16-bit DOS programming. And if you're into learning a little about assembly language and bytecode and such, "debug" is a wonderful tool for immersing yourself in the innards of the system. To use it, type "debug" at the command prompt. Once in the program, type "?" for help with the commands. One good thing to play around with the the memory dump feature. For example, type:
d c000:0
to see a text string describing your video card. This can be very useful if you have no idea what kind of video card you are working with, but you need to find a driver for it. If the text continues, type "d" again to view it. Another occasionally useful trick is to do:
d f000:fff0
to see the creation date for your BIOS