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In the beginning, there was darkness; and out of that darkness there came a light. “A:\”, it said, and the world was happy.

MSDOS

MSDOS (Microsoft Disk Operating System) was Microsoft’s first operating system for the PC. It dominated the scene through the ’80s, and carries on till today, albeit in a less important role. It was actually developed by Seattle Computer Products, who called it QDOS—the Quick and Dirty Operating System. Microsoft then bought the system from them for just $50,000 and changed it to MSDOS. DOS was a simple system—it only let one program to run at a time, and gave it full control of the machine. If a program crashed, there was no other option but to reboot.

DOS gave ‘drive letters’ to each disk drive on your system—‘A:’ and ‘B:’ were the floppy drives, and if you were lucky enough to have a hard drive, it would be called ‘C:’. DOS organized these disks into files and directories, and used the FAT (File Allocation Table) to keep tabs on them.

DOS filenames consisted of two parts—an eight-letter name, and a three-letter extension, both separated by a dot ‘.’—For example, “filename.ext”. The file’s extension told DOS what type of file it was, and which program to use to open it.

Users spoke to DOS using a Command Line Interface. Put simply, DOS would ask for a command using the Command Prompt, and you would type in what you wanted it to do. If you had lots of commands which you needed to run over and over again, you would used the handy ‘batch’ file—just type in all your commands into the batch file, save it, and now all you needed to do was to tell DOS to run this batch file, and it would run all your commands without disturbing you.

DOS has always been part of its successors, and Microsoft only ceased further development on it in the year 2000.

The heart of MSDOS