86DOS

86-DOS, originally known as QDOS (Quick and Dirty Operating System), is a 16-bit operating system developed by Seattle Computer Products (SCP) for the Intel 8086/8088 family. Created in 1980–1981 as a CP/M-86–compatible OS with a DOS-like command interface, it provided a practical, affordable solution for running software on early microcomputers built around the 8086 processor.

Tim Paterson led the development of QDOS, which SCP released for its 8086-based machines. In 1981 Microsoft acquired the rights, renamed it 86-DOS, and licensed it to IBM for their PC-DOS product line. IBM PC-DOS and Microsoft MS-DOS 1.0 were released in 1981, establishing the DOS family as a standard for x86 PCs.

86-DOS featured a simple command-line interface and a small set of system utilities, with a file system based on the FAT approach and 8.3-style filenames. It offered CP/M-86–style programming compatibility to ease migration for developers transitioning from CP/M, while laying groundwork for the DOS ecosystem that followed.

Legacy: 86-DOS is regarded as the direct predecessor of MS-DOS, and its sale to Microsoft is a notable event in personal-computer history. The DOS line it helped launch dominated early PC software and shaped compatibility and file-system conventions that persisted through MS-DOS and its successors into the Windows era.