86-DOS

86-DOS (known internally as QDOS, for Quick and Dirty Operating System) is a discontinued operating system developed and marketed by Seattle Computer Products (SCP) for its Intel 8086-based computer kit.

86-DOS shared a few of its commands with other operating systems such as OS/8 and CP/M, which made it easy to port programs from the latter. Its application programming interface was very similar to that of CP/M. The system was licensed and then purchased by Microsoft and developed further as MS-DOS and PC DOS.

86-DOS was created because sales of the Seattle Computer Products 8086 computer kit, demonstrated in June 1979 and shipped in November, were languishing due to the absence of an operating system. The only software that SCP could sell with the board was Microsoft's Standalone Disk BASIC-86, which Microsoft had developed on a prototype of SCP's hardware. SCP wanted to offer the 8086-version of CP/M that Digital Research had initially announced for November 1979, but it was delayed and its release date was uncertain. This was not the first time Digital Research had lagged behind hardware developments; two years earlier it had been slow to adapt CP/M for new floppy disk formats and hard disk drives. In April 1980, SCP assigned 24-year-old Tim Paterson to develop a substitute for CP/M-86.

Using a CP/M-80 manual as reference, Paterson modeled 86-DOS after its architecture and interfaces, but adapted to meet the requirements of Intel's 8086 16-bit processor, for easy (and partially automated) source-level translatability of the many existing 8-bit CP/M programs; porting them to either DOS or CP/M-86 was about equally difficult and eased by the fact that Intel had already published a method that could be used to automatically translate software from the Intel 8080 processor, for which CP/M had been designed, to the new 8086 instruction set. At the same time he made a number of changes and enhancements to address what he saw as CP/M's shortcomings. CP/M cached file system information in memory for speed, but this required a user to force an update to a disk before removing it; if the user forgot, the disk would become corrupt. Paterson took the safer, but slower approach of updating the disk with each operation. CP/M's PIP command, which copied files, supported several special file names that referred to hardware devices such as printers and communication ports. Paterson built these names into the operating system as device files so that any program could use them. He gave his copying program the more intuitive name COPY. Rather than implementing CP/M's file system, he drew on Microsoft Standalone Disk BASIC-86's File Allocation Table (FAT) file system.

By mid-1980 SCP advertised 86-DOS, priced at US$95 for owners of its US$1,290 8086-board and US$195 for others. It touted the software's ability to read Zilog Z80 source code from a CP/M disk and translate it to 8086 source code, and promised that only "minor hand correction and optimization" was needed to produce 8086 binaries.

In October 1980, IBM was developing what would become the original IBM Personal Computer. CP/M was by far the most popular operating system in use at the time, and IBM felt that it needed CP/M in order to compete. IBM's representatives visited Digital Research and discussed licensing with Digital Research's licensing representative, Dorothy Kildall (née McEwen), who hesitated to sign IBM's non-disclosure agreement. Although the NDA was later accepted, Digital Research would not accept IBM's proposal of US$250,000 in exchange for as many copies as IBM could sell, insisting on the usual royalty-based plan. In later discussions between IBM and Bill Gates, Gates mentioned the existence of 86-DOS, and IBM representative Jack Sams told him to get a license for it.^{[citation needed]}

Microsoft purchased a non-exclusive license for 86-DOS from Seattle Computer Products in December 1980 for US$25,000.^{[citation needed]} In May 1981, it hired Tim Paterson to port the system to the IBM PC, which used the slower and less expensive Intel 8088 processor and had its own specific family of peripherals. IBM watched the developments daily, submitting over 300 change requests before it accepted the product and wrote the user manual for it.

In July 1981, a month before the PC's release, Microsoft purchased all rights to 86-DOS from SCP for US$50,000. It met IBM's main criteria: it looked like CP/M, and it was easy to adapt existing 8-bit CP/M programs to run under it, notably thanks to the TRANS command which would translate source files from 8080 to 8086 machine instructions. Microsoft licensed 86-DOS to IBM, and it became PC DOS 1.0. This license also permitted Microsoft to sell DOS to other companies, which it did. The deal was spectacularly successful, and SCP later claimed in court that Microsoft had concealed its relationship with IBM in order to purchase the operating system cheaply. SCP ultimately received a US$1 million settlement payment.