16BitOS.COM contains a wealth of information about DOS and its release history. There are many fine sites on the web that provide information related to DOS. It is not our place to attempt to detract from the work of others, and certainly anything that contributes to the critical mass of the DOS knowledgebase is welcome in the technical community at large.

In order for you to understand our methodology, it is important to cover some things early on. Perhaps the most important of all is just what exactly we define as "DOS". Simply put, this site recognizes all DOS releases from Microsoft® and IBM® as the only legitimate descendants. Other clones, such as FreeDOS, DR-DOS (OpenDOS), ProDOS, 4DOS, NDOS, etc. either came after the fact or were descendants from other branches of operating system trees. We recommend you read our development history pages, which will clearly validate how we came to arrive at this decision.

Another issue that frequently comes up is "DOS" that is bundled with Microsoft® Windows®. These are not true stand-alone operating systems. Rather, starting with Windows® 95 the command line environment was backward compatible for 16-bit applications, but with 32-bit optimizations. Because these are included in Windows® as a component, rather than independent of it, these are not a true continuation of the DOS bloodline. We therefore do not include them on this site, considering them to be a gray area, despite the fact they are obviously genealogic descendants.

We have also seen third parties reverse engineer or rip out the command interpreters from Windows® and claim it to be newer "releases" of MS-DOS. These are not officially licensed, despite their attempts at legitimacy by including Microsoft® version 6.xx binaries with third party utilities and installers. The final releases of DOS, according to our criteria, were the MS-DOS 6.22 Step-Up in May, 1994, and PC-DOS 7.0 Revision 1, released in April of 1998.

Genealogy is primarily concerned with a specific historic origin, the descendents of that origin, and any offshoots that occur along the way. We have refined that definition with specific purity. We are aware that there will always be those who debate and disagree, but our recognition of the critical mass for DOS origin occurs when Microsoft buys 86-DOS in 1980 and proceeds to retool it for the original IBM PC - see our development history pages for more detailed information.

This site fills the specific void that historically chronicles the vital statistics of product releases. At the time of launching this site, there was nothing on the Internet that specifically focused on version and development history in detail. It is this area where our efforts have been directed, and with considerable success. We believe you will find our site format and content are both professional and comprehensive, particularly if you are a collector.

This site covers three areas of DOS reference. The first is the individual versions themselves - the bulk of the project. As you will see, we have held an extensive private collection, and the majority of the data cataloged on this site was collected first-person by us in our own lab, giving us absolute validity on the results. We have also included for background information a three-part essay on the pre-history of DOS and the events that led to its creation. And third, we have included an overview of the DOS architecture and how it interacts with personal computers. This is more technical and explains the boot process and how it controls hardware.

To your left is the navigation menu. This index guides you to these three areas. Each page will display in this frame on the right and the menu will be present at all times. The menu is coded for java and non-java support, depending on your browser. Scrolling is enabled on each page to allow horizontal and vertical control to view the content when it exceeds the page format. We do not use any pop-up windows, cookies, or spyware on this site, as we are personally against any content that detracts from your research experience or collects data without your consent.

Why do you list DOS from both IBM® and Microsoft® Corporation?

When IBM® first decided to introduce the PC, they needed an operating system and signed a contract with Microsoft® Corporation to develop it. This relationship continued throughout the history of the product. We list both company releases because historically they are co-dependent.

Did Microsoft® Corporation write every version of DOS?

No. Microsoft® Corporation wrote the majority of DOS releases, but not all of them. In 1993 with the release of PC DOS®, IBM® released its own DOS (with legacy code from Microsoft® included). They continued to develop PC DOS® beyond the end of life point for MS-DOS® as a stand-alone 16-bit operating system.

Did Bill Gates write DOS?

DOS had several engineers working on it before Microsoft® Corporation purchased the rights. Bill Gates, to his credit, was a qualified and talented programmer, but he did not write DOS (he did write a custom BASIC for MITS). If you begin the engineering pedigree with Microsoft's® acquisition of the product from Seattle Computing, the lead programmer was Robert O'Rear, who ported the OS from 8" to 5.25" media. Tim Paterson was later hired by Microsoft® to continue development in the closing months before IBM® certified the product for release.

What is the manufacturing sequence for DOS versions?

Initially, the core code was written to match the requirements for controlling the hardware platform. This control was built around the Intel x86 processor. As core code was incrementally developed, other code was written to augment the features of the operating system itself. This combined code was then designated as alpha code and sent to quality assurance labs for initial testing. Certifying the OS was sufficiently capable of working, the code was then designated a beta and released to third parties, usually programmers and dealers to test it under real-life conditions. When the beta testing phase was completed, marketing and promotion efforts ramped up to coincide with the planned version release after the final code freeze. Thereafter, each release was an incremented modification based on the previous release, the hardware platform of the time, and the features designed and included.

What is an "OEM" release of DOS, vs. a base or upgrade release?

OEM, or "Original Equipment Manufacturer", is a term to designate a non-IBM® computer. Because IBM® chose to use industry-standard hardware to build the PC, other manufacturers were able to engineer systems that paralleled the BIOS and the system design. This led to "IBM clones", Compaq® and Zenith® being some of the first. An OEM DOS may contain special boot files for specific BIOS calls, as well as files related to specific systems that would not otherwise be found on a regular IBM DOS® release. With later versions, the term OEM was loosely fitted to mean an exact DOS version copy but branded for release with the equipment of specific companies (actual OEM releases were discontinued after version 4.00, as "100% IBM compatible" had been achieved in the industry). A base DOS release is a complete, stand-alone DOS package that can be installed on a blank hard drive. An upgrade release is designed to install over an existing version and modifies the necessary files, but unto itself cannot be installed stand-alone.

What are major vs. minor releases of DOS?

A major DOS release occurs under several conditions. Whenever improvements to hardware are introduced (memory, storage, processor, or peripherals), DOS has been modified to work with these devices. Major releases also occur to address problems that were significant enough in a previous release to rewrite and release as a major fix. Minor releases, on the other hand, are used mostly for bug fixes and adding last-minute hardware or feature support after a major release has occurred. There are also minor.minor releases. These normally designate modifications for OEM platforms.

What are release dates?

One would assume a release date is the date the DOS version was made available to the public. This is not quite true, and purists continue to debate this particular topic. There are three specific milestones in a DOS release. The first is when the codefreeze occurs. This means the version went through a final testing phase, and was then ready to ship. Post-codefreeze DOS versions are identified by the most recent filedate on a given disk as the last date a change was made. This qualifies as a benchmark date to identify it was ready for public use.

The second is when the manufacturer releases an announcement letter or marketing flyer. However, there is ample precedent that announcement dates do not correspond with the date the DOS was actually publicly in-hand. And third, there is the available date. This is the date manufacturers strategically assume the public availability of the product will occur, based on revised estimates or projections. The majority of DOS release dates have been the announcement date, giving the impression versions were released to the public when in fact they were not.

We use the codefreeze dates as our release dates because they are the tightest forensic evidence of the date the version was actually created. From a genealogical standpoint it is more important to have the exact date of birth vs. the approximate.

How do I find the specific version number for a given release?

There are two ways to identify the version number. The first, and simplest way, is to type 'VER' at a DOS prompt. This command calls an interrupt service that queries a register value and returns the version identifier string to your screen. This information is pulled from the command.com file. The second method is to use a hex editor and examine the DOS kernel file, either IBMDOS.COM or MSDOS.COM. The kernel file will contain a ASCII version identifier. This is notable, because some releases, particularly minor ones, changed the command.com file but not the kernel file. It then becomes a matter of identifying the version kernel and the version command interpreter together. Other than forensic considerations, the 'VER' command is sufficient to establish a particular version (with exceptions - see IBM DOS 4.01).

Your site only covers domestic U.S. product releases. Why?

DOS is an international product. Some international versions have different version numbers than their American counterparts. None the less, the international releases are virtually identical to their U.S. cousins, except for specific codepage support for local languages, currency, and keyboard layouts, MS-DOS version 4.10 being a maverick exception as best we can tell.

What criteria did you use for version analysis?

Specifically, we felt there were several characteristics about individual versions both required and noteworthy. After considering a number of version features, we decided to use the following list of identifiers:

Is DOS still supported by the manufacturers?

No. While both IBM® and Microsoft® Corporation continue to offer limited support documentation on their websites, actual product support was terminated as the focus shifted to Microsoft Windows®. It is no longer possible to obtain this support directly from the manufacturers. There continues to be a handful of online third party resources that provide support, but from a reference only capacity.

Was DOS ever released on a CD?

Yes, but only once. IBM® released PC DOS 2000 on a CD in its final release. The equivalent contents was contained on 6 high density 1.44 floppies.

How do I determine the value of a given release I have in my possession?

Our site provides a list of approximate rarity and values associated with each version. These are based on prevailing auction and collector costs to obtain these releases, and they are an accurate estimate within the limitations of otherwise continuous updating. These values are given as Mint (fully intact, in perfect condition), VG (for Very Good, meaning fully intact, only minor signs of wear), and G (for Good - fully or almost completely intact, used, with some variations such as creased pages, worn labels, etc.).

You should know that only a subset of DOS releases are rare and valuable. Most releases, particularly those that came towards the end of the product lifecycle are rated at face value of the purchase price. The very early releases, and some hard to find in the middle, command the best price. It should be noted the value of lesser releases increases substantially if entire runs are collected, i.e. MS-DOS 6.00 through 6.22, including Base, Upgrade, Step-Ups, and Supplementals.

What is the "rarest" version of DOS?

Based on our collecting efforts, which were likely the most serious effort ever made on this scale by anyone, we have concluded that MS-DOS® version 2.25 is perhaps the world's rarest version. We are prepared to back that up with cash if anyone is fortunate enough to find a complete, bootable version. We must emphasize before people get too excited that we encountered more than 20 false positives on this version in the course of attempting to find it. At this point in time, its elusiveness yields the distinction of virtual non-existence.

Are there other DOS collector resources on the web?

We found a rather anemic representation of sites available around the world specifically for collectors or those seeking to learn about DOS genealogy. 16bitos.com is proud to claim the distinction of being the most comprehensive resource of its kind in the world, in terms of product identification and history.