PCDOS

PCDOS, short for Personal Computer Disk Operating System, is IBM’s branded version of the early DOS operating system for the IBM PC line. It was introduced in 1981 alongside the IBM PC and was based on 86-DOS, the operating system originally developed by Seattle Computer Products and later acquired by Microsoft as the basis for MS-DOS. IBM licensed the MS-DOS technology from Microsoft and released PC-DOS 1.0, branding it for IBM hardware.

In practice, PC-DOS and MS-DOS began as very similar systems with shared core code, reflecting the same command set, disk formats, and software compatibility. Over time, IBM’s and Microsoft’s releases diverged in branding and licensing terms, while maintaining a high degree of binary and API compatibility for many years. IBM continued to publish PC-DOS alongside MS-DOS, extending functionality to support features such as hard disks, subdirectories, and evolving FAT-based file systems in later PC-DOS versions.

Technically, PC-DOS ran on 8086-based PC hardware, used the FAT file system, and provided a command-line interface with programs packaged as .EXE or .COM files. Its ecosystem supported a wide range of early PC software, utilities, and development tools, helping to standardize software development for IBM-compatible machines.

Legacy: PC-DOS played a central role in the IBM-PC era and in establishing the long-running DOS-compatible software ecosystem. It influenced subsequent MS-DOS development and the broader Windows-DOS integration in the 1990s.