computer science

DR-DOS

DR-DOS is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand DR-DOS rather than just read about it. In short: DR-DOS is a disk operating system for IBM PC compatibles, originally developed by Gary A. Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86.

Key takeaways

DR-DOS belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect DR-DOS to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of DR-DOS from memory before moving on to harder problems.

Reference excerpt

DR-DOS is a disk operating system for IBM PC compatibles, originally developed by Gary A. Kildall's Digital Research and derived from Concurrent PC DOS 6.0, which was an advanced successor of CP/M-86. Upon its introduction in 1988, it was the first operating system that attempted to be compatible with IBM PC DOS and MS-DOS. The first release was version 3.31, named to match MS-DOS's then-current version. DR DOS 5.0 was released in 1990 as the first to be sold in retail; it was critically acclaimed and led to DR DOS becoming the main rival to Microsoft's MS-DOS, who quickly responded with its own MS-DOS 5.0 but releasing over a year later. It introduced a graphical user interface layer called ViewMAX. DR DOS 6.0 was released in 1991; then with Novell's acquisition of Digital Research, the following version was named Novell DOS 7.0 in 1994. After another sale, to Caldera, updated versions were released partly open-source under the Caldera moniker, and briefly as OpenDOS. The previously last version for desktops, Caldera DR-DOS 7.03, was released in 1999, after which the software was sold to Embedded Systems by Caldera and then by DeviceLogics. In January 2022, Whitehorn Ltd. Co. registered the DR DOS trademark. Since 2026 it has been releasing beta versions of DR DOS 9.0, an operating system written from scratch and not based on the code of previous versions.

History

Origins in CP/M Digital Research's original CP/M for the 8-bit Intel 8080- and Z80-based systems spawned numerous spin-off versions, most notably CP/M-86 for the Intel 8086/8088 family of processors. Although CP/M had dominated the market since the mid-1970s, and was shipped with the vast majority of non-proprietary-architecture personal computers, the IBM PC in 1981 brought the beginning of what was eventually to be a massive change. IBM originally approached Digital Research in 1980, seeking an x86 version of CP/M. However, there were disagreements over the contract, and IBM withdrew. Instead, a deal was struck with Microsoft, who purchased another operating system, 86-DOS, from Seattle Computer Products (SCP). This became Microsoft MS-DOS and IBM PC DOS. 86-DOS's command structure and application programming interface imitated that of CP/M 2.2 (with BDOS 2.2). Digital Research threatened legal action, claiming PC DOS/MS-DOS to be too similar to CP/M. In early 1982, IBM settled by agreeing to sell Digital Research's x86 version of CP/M, CP/M-86, alongside PC DOS. However, PC DOS sold for US$40 while CP/M-86 had a $240 price tag. The proportion of PC buyers prepared to spend six times as much to buy CP/M-86 was very small, and the limited availability of compatible application software, at first in Digital Research's favor, was only temporary. Digital Research fought a long losing battle to promote CP/M-86 and its multi-tasking multi-user successors MP/M-86 and Concurrent CP/M-86, and eventually decided that they could not beat the Microsoft-IBM lead in application software availability, so they modified Concurrent CP/M-86 to allow it to run the same applications as MS-DOS and PC DOS. This was shown publicly in December 1983 and shipped in March 1984 as Concurrent DOS 3.1 (a.k.a. CDOS with BDOS 3.1) to hardware vendors. While Concurrent DOS continued to evolve in various flavors over the years to eventually become Multiuser DOS and REAL/32, it was not specifically tailored for the desktop market and too expensive for single-user applications. Therefore, over time two attempts were made to sideline the product: In 1985, Digital Research developed DOS Plus 1.0 to 2.1, a stripped-down and modified single-user derivative of Concurrent DOS 4.1 and 5.0, which ran applications for both platforms, and allowed switching between several tasks as did the original CP/M-86. Its DOS compatibility was limited, and Digital Research made another attempt, this time a native DOS system. This new disk operating system was launched in 1988 as DR DOS. Although DRI was based in Pacific Grove and later in Monterey, California, USA, the work on DOS Plus started in Newbury, Berkshire in the UK, where Digital Research Europe had its OEM Support Group located since 1983. Beginning in 1986, most of the operating system work on Concurrent DOS 386 and XM, Multiuser DOS, DR DOS and PalmDOS was done in Digital Research's European Development Centre (EDC) in Hungerford, Berkshire. Later on some work was also done by Digital Research GmbH in Munich, Germany.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with DR-DOS

Start with the simplest possible case. Write down what DR-DOS claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to DR-DOS before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about DR-DOS ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of DR-DOS

In research: DR-DOS appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses DR-DOS in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: DR-DOS is common in secondary-school and first-year university syllabi. It links to neighbouring topics 1988 software, Caldera (company) operating systems, DOS variants, so understanding it makes those chapters shorter.
In everyday life: Look for DR-DOS outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study DR-DOS in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what DR-DOS means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain DR-DOS out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is DR-DOS in simple terms?

Why does DR-DOS matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study DR-DOS?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on DR-DOS.