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MS-DOS: the story on HearLore | HearLore
MS-DOS
In just six weeks during the summer of 1980, a young programmer named Tim Paterson wrote an operating system that would eventually dominate the personal computer world. Paterson worked for Seattle Computer Products, a small hardware company struggling to sell its 8086-based boards. He needed an operating system to make his hardware attractive to buyers, so he created 86-DOS, a direct clone of Digital Research's CP/M but adapted for the Intel 8086 processor. The project was a race against time, and Paterson delivered the code in August 1980, just as the company needed to ship its first systems. The operating system included two critical innovations over its predecessor: improved disk sector buffering logic and the introduction of the FAT12 file system, which allowed for more efficient storage management on floppy disks.
Microsoft, then a small company primarily known for selling programming languages like BASIC, found itself in a desperate position when IBM approached them in 1981 to provide an operating system for the upcoming IBM Personal Computer. Bill Gates and Paul Allen moved quickly to acquire 86-DOS from Seattle Computer Products in July 1981 for 50,000 dollars. They did not rewrite the code from scratch; instead, they licensed the existing product, kept the version number, and renamed it MS-DOS. This acquisition transformed Microsoft from a language vendor into a software giant. The deal was so rushed that Microsoft did not initially own the copyright to the code, but they secured the rights to license it to IBM. By August 1981, IBM released the system as PC DOS 1.0, bundled with the IBM 5150, the first IBM PC. The simplicity of the system belied its future impact, as it was designed to run on floppy disks and support only the most basic hardware configurations of the time.
The Great Divergence
The partnership between Microsoft and IBM was intended to be a seamless collaboration, but it quickly fractured into two separate development tracks. While IBM and Microsoft initially developed MS-DOS and PC DOS in parallel, the two products began to diverge significantly after twelve years, finally separating in 1993 with recognizable differences in compatibility, syntax, and capabilities. The root of this split lay in the original licensing agreement, which allowed Microsoft to sell the same operating system to other computer manufacturers. IBM wanted exclusive rights, but Microsoft insisted on retaining the ability to license the software to the broader market. This decision created a situation where IBM PC DOS and MS-DOS were functionally similar but technically distinct products.
As the market evolved, the divergence became more pronounced. IBM focused on its own hardware and the PC DOS line, while Microsoft pushed MS-DOS to other manufacturers. By 1988, competing products like DR-DOS emerged, challenging the dominance of the Microsoft-IBM alliance. The situation became so complex that Compaq, a major clone manufacturer, had to develop its own version called COMPAQ-DOS to ensure compatibility with IBM hardware. Compaq engineers discovered that MS-DOS and PC DOS were not identical, causing compatibility issues for their machines. Microsoft eventually discontinued its internal development of MS-DOS and resold Compaq's software as MS-DOS, allowing Compaq to remain slightly more compatible with the IBM PC than other clone makers. This strategic maneuvering ensured that Microsoft maintained control over the market while IBM lost its exclusive hold on the operating system.
Who created the original operating system that became MS-DOS?
Tim Paterson created the original operating system known as 86-DOS during the summer of 1980 while working for Seattle Computer Products. Paterson delivered the code in August 1980 to help the company sell its 8086-based boards.
When did Microsoft acquire 86-DOS and rename it MS-DOS?
Microsoft acquired 86-DOS from Seattle Computer Products in July 1981 for 50,000 dollars. Bill Gates and Paul Allen licensed the existing product and renamed it MS-DOS without rewriting the code from scratch.
When did MS-DOS and PC DOS officially separate into distinct products?
MS-DOS and PC DOS began to diverge significantly after twelve years and finally separated in 1993. The split occurred because the original licensing agreement allowed Microsoft to sell the operating system to other computer manufacturers while IBM wanted exclusive rights.
When did Microsoft stop providing support for all versions of MS-DOS?
Microsoft declared all versions of MS-DOS 6.22 and older obsolete on the 31st of December 2001. Support for MS-DOS 7.0 ended on the same date, and support for MS-DOS 7.10 and MS-DOS 8.0 ended on the 11th of July 2006.
When did Microsoft release the source code for MS-DOS to the public?
Microsoft released the source code for SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11 on the 25th of March 2014. The company later re-licensed the code under the MIT License on the 28th of September 2018 and released the code for MS-DOS 4.00 on the 25th of April 2024.
In the early days of the personal computer revolution, speed was the ultimate currency, and the operating system often took a back seat to raw performance. Programmers frequently bypassed standard operating system calls to communicate directly with hardware, a practice that made software run faster but created a fragmented ecosystem. Games, in particular, pushed the limits of contemporary hardware, often requiring direct access to the processor and memory. This approach meant that software written for one machine would not run on another, even if both used MS-DOS. The market eventually shifted toward IBM-compatible architecture, as software written to communicate directly with PC hardware without using standard operating system calls ran much faster on true PC-compatibles. Non-PC-compatible 808x machines were too small a market to have fast software written for them alone, and the market remained open only for IBM PCs and machines that closely imitated their architecture.
Microsoft's strategy to create a single version of MS-DOS for a fixed hardware platform was driven by the need to standardize the market. The company designed MS-DOS with a modular structure, including internal device drivers and installable device drivers for other devices loaded at boot time. This allowed different hardware manufacturers to create their own versions of MS-DOS, but the goal was to eventually converge on a single standard. The result was a market dominated by IBM PCs and clones, all running a single version of MS-DOS compatible only with PCs. This standardization allowed software developers to write programs that could run on any IBM-compatible machine, creating a vast ecosystem of applications and games. The shift from a fragmented market to a unified standard was a pivotal moment in the history of personal computing, setting the stage for the dominance of the IBM PC architecture.
The FUD Campaign
The battle for the operating system market was not won solely through superior technology but also through aggressive marketing tactics. Microsoft employed a strategy known as FUD, or fear, uncertainty, and doubt, to undermine its competitors, particularly Digital Research's DR-DOS. In October 1990, shortly after the release of DR-DOS 5.0, Microsoft began leaking information about future versions of MS-DOS, including features that were not yet developed. Brad Silverberg, then Vice President of Systems Software at Microsoft, wrote a forceful letter to PC Week denying that Microsoft was engaged in FUD tactics, claiming that the feature enhancements of MS-DOS version 5.0 were decided and development was begun long before they heard about DR-DOS 5.0. This denial was widely seen as a cover for the company's aggressive marketing strategy.
The impact of this campaign was devastating for Digital Research. Microsoft's pre-announcements of future versions of MS-DOS effectively killed sales of DR-DOS, as customers waited for the promised features. The situation escalated when Microsoft announced the pending release of MS-DOS 5.0 in May 1990, which stifled DR-DOS sales until the actual release of MS-DOS 5.0 in June 1991. Digital Research responded by releasing DR-DOS 6.0, which sold well until the pre-announcement of MS-DOS 6.0 again stifled sales. The legal and business battles that followed were intense, with Microsoft accused of orchestrating leaks to create uncertainty in the market. The outcome was a clear victory for Microsoft, as DR-DOS never managed to gain a significant foothold in the market, and Microsoft's dominance was cemented.
The Compression Wars
The legal battles over disk compression utilities marked a turning point in the history of MS-DOS. In response to Digital Research's DR-DOS 6.0, which bundled SuperStor disk compression, Microsoft opened negotiations with Stac Electronics, the vendor of the most popular DOS disk compression tool, Stacker. Stac engineers had shown Microsoft part of the Stacker source code during the due diligence process, but Stac was unwilling to meet Microsoft's terms for licensing Stacker and withdrew from the negotiations. Microsoft chose to license Vertisoft's DoubleDisk, using it as the core for its DoubleSpace disk compression utility, which was included in MS-DOS 6.0 and 6.20.
The legal fallout was immediate and severe. Stac successfully sued Microsoft for patent infringement regarding the compression algorithm used in DoubleSpace. This resulted in the 1994 release of MS-DOS 6.21, which had disk compression removed. Shortly afterwards came version 6.22, with a new version of the disk compression system, DriveSpace, which had a different compression algorithm to avoid the infringing code. The legal battle highlighted the aggressive tactics Microsoft employed to maintain its market dominance, as the company was willing to engage in litigation to protect its interests. The outcome was a significant blow to Stac, which lost its position in the market, and a victory for Microsoft, which retained control over the disk compression utility. The incident also underscored the importance of intellectual property in the software industry, as companies began to take legal action to protect their innovations.
The Silent Death
The end of MS-DOS was not a dramatic event but a slow, silent decline. The introduction of Windows 3.0 in 1990, with its easy-to-use graphical user interface, marked the beginning of the end for the command-line driven MS-DOS. With the release of Windows 95, an integrated version of MS-DOS was used for bootstrapping, troubleshooting, and backwards-compatibility with old DOS software, particularly games, and no longer released as a standalone product. In Windows 95, the DOS, called MS-DOS 7, could be booted separately, without the Windows GUI, but this capability was retained through Windows 98 Second Edition. Windows Me removed the capability to boot its underlying MS-DOS 8.0 alone from a hard disk, but retained the ability to make a DOS boot floppy disk, called an Emergency Boot Disk.
The final blow came on the 31st of December 2001, when Microsoft declared all versions of MS-DOS 6.22 and older obsolete and stopped providing support and updates for the system. Support for MS-DOS 7.0 also ended when Windows 95 extended support ended on the same date. As MS-DOS 7.10 and MS-DOS 8.0 were part of Windows 98 and Windows Me, respectively, support ended when Windows 98 and ME extended support ended on the 11th of July 2006, thus ending support and updates of MS-DOS from Microsoft. The creation of the MS-DOS startup disk was then carried over to later versions of Windows, with the majority of its contents remaining unchanged from its introduction in Windows XP. Starting with Windows 10, the ability to create a MS-DOS startup disk has been removed, and so either a virtual machine running MS-DOS or an older version must be used to format a floppy disk. The last remaining components related to MS-DOS was the NTVDM component, which was removed entirely in Windows starting with Windows 11 as the operating system dropped support for 32-bit processors in favor of being solely offered in 64-bit versions only. This effectively ended any association of MS-DOS within Microsoft Windows after 36 years.
The Code Unlocked
In a surprising turn of events, Microsoft released the source code for MS-DOS to the public, making it available for education and experimentation. On the 25th of March 2014, Microsoft made the code to SCP MS-DOS 1.25 and a mixture of Altos MS-DOS 2.11 and TeleVideo PC DOS 2.11 available to the public under the Microsoft Research License Agreement, which makes the code source-available, but not open source as defined by Open Source Initiative or Free Software Foundation standards. The company later re-licensed the code under the MIT License on the 28th of September 2018, making these versions free software. Microsoft later released the code for MS-DOS 4.00 on the 25th of April 2024, under the same license. The purpose of this release, according to Microsoft, is mainly for education and experimentation with historic operating systems and for new programmers to gain an understanding of how low-level software works, both historic and current.
The release of the source code was a significant moment in the history of MS-DOS, as it allowed the public to study the inner workings of one of the most influential operating systems in history. The code was released on GitHub, and users were encouraged to fork the repository and make their own modifications. The release also highlighted the importance of preserving historical software, as the code provided a window into the early days of personal computing. The decision to release the code was a departure from Microsoft's usual practices, as the company had previously kept the source code of MS-DOS proprietary. The release of the code was a testament to the enduring legacy of MS-DOS, as it continued to be studied and appreciated by programmers and historians alike.