Editing DR-DOS (section)

===Origins in CP/M===
[[Digital Research]]'s original [[CP/M]] for the 8-bit [[Intel 8080]]- and [[Zilog Z80|Z80]]-based systems spawned numerous spin-off versions, most notably CP/M-86 for the [[Intel 8086]]/[[Intel 8088|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&nbsp;DOS]]. 86-DOS's command structure and application programming interface imitated that of [[CP/M 2.2]] (with [[Basic Disk Operating System|BDOS]] 2.2). Digital Research threatened legal action, claiming PC&nbsp;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&nbsp;DOS. However, PC&nbsp;DOS sold for {{currency|amount=40|code=USD|fmt=gaps|linked=yes}} 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.<ref name="podtech"/>

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&nbsp;DOS.

This was shown publicly in December 1983<ref name="DRI_1984_PCMODE"/> and shipped in March 1984 as [[Concurrent DOS 3.1]] (a.k.a. CDOS with BDOS 3.1) to hardware vendors.<ref name="DRI_1984_CDOS31"/> 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&nbsp;Plus 1.0]] to [[DOS&nbsp;Plus 2.1|2.1]], a stripped-down and modified single-user derivative of [[Concurrent DOS 4.1]] and [[Concurrent DOS 5.0|5.0]], which ran applications for both platforms, and allowed switching between several tasks<ref name="DOS Plus"/><ref name="Wein_2009_DOSPLUS"/> as did the original CP/M-86. Its DOS compatibility was limited, and Digital Research made another attempt, this time a native DOS system.<ref name="Wein_2009_DOSPLUS"/> This new disk operating system was launched in 1988 as DR&nbsp;DOS.

Although DRI was based in [[Pacific Grove, California|Pacific Grove]] and later in [[Monterey, California|Monterey]], California, USA, the work on DOS&nbsp;Plus started in [[Newbury, Berkshire|Newbury]], Berkshire in the UK, where Digital Research Europe had its OEM Support Group located since 1983.<ref group="nb" name="NB_Office-Locations"/> Beginning in 1986, most of the operating system work on [[Concurrent DOS 386]] and [[Concurrent DOS XM|XM]], Multiuser DOS, DR&nbsp;DOS and PalmDOS was done in Digital Research's European Development Centre (EDC) in [[Hungerford, Berkshire|Hungerford]], Berkshire.<ref group="nb" name="NB_Office-Locations"/> Later on some work was also done by Digital Research GmbH in [[Munich]], Germany.