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In 1980, IBM was working on developing a personal computer. They discussed ideas for the computer with Bill Gates who ultimately suggested that they look into using Digital Research's CP/M (Control Program for Microcomputers) operating system. IBM wasn't able to work out a deal with Digital Research, so they turned back to Microsoft. Microsoft then bought the rights to QDOS (Quick and Dirty Operating System), an operating system that was based on CP/M, and used it as a model to build MS-DOS.¹  In August of 1981, MS-DOS 1.0 began shipping with the IBM Personal Computer, although Microsoft still retained the right to sell it themselves as a separate product.^{1, 30}

MS-DOS is a command line driven operating system, meaning it is controlled by typing various commands at a system prompt. Version 1.0 does not support a hierarchical directory structure (you can't create subdirectories on a disk), hard drives, double-sided floppy disks or high density floppy disks, all features that were considered necessities soon after its release. Support for double-sided floppy disks was added in MS-DOS 1.25 in 1982. Support for IBM 10 MB (megabyte) hard drives and 360 KB (kilobyte) double-density 5.25-inch floppy disks, as well as the ability to create subdirectories, was added in version 2.0 in 1983, and foreign and extended character support was included with version 2.11 the same year.²⁹  Without subdirectories (or folders, as they are commonly called today), files can not be organized in any meaningful fashion and are all listed together on the disk, making it difficult to quickly find any particular file when there are many on a disk. However, considering that the maximum disk size DOS 1.x could support was 320 KB (about 90 pages of text total), this was not too much of an issue at the time.

MS-DOS 3.0 was released in 1984 with the ability to read 1.2 MB 5.25-inch high-density floppy disks and 32 MB hard drives, and in the same year version 3.1 offered network support. In 1986, version 3.2 provided support for 720 KB 3.5-inch floppy disks. MS-DOS 3.3 allowed the use of 1.44 MB 3.5-inch high-density floppies and hard drive partitions.^{2, 29}  Hard drive partitions allow people to use a bigger hard drive than the operating system supports. When a drive is partitioned, it is broken up into two or more sections (partitions) that the operating system sees as completely separate hard drives. For example, in order to take advantage of all the space on a 50 MB hard drive using MS-DOS 3.3 (which only supports up to 32 MB drives), the drive would have to be partitioned, resulting in a 32 MB partition referred to as the C drive and an 18 MB partition referred to as the D drive. MS-DOS sees C and D as two distinct hard drives that are within the 32 MB size limit imposed by the operating system. When hard drives started to become available in sizes larger than about 500 MB, partitions also served the purpose of allowing files to take up less space on the hard drive.

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