Editing RSX-11 (section)

===RSX-11D and IAS=== 
The porting effort first produced small paper tape based real-time executives (RSX-11A, RSX-11C) which later gained limited support for disks (RSX-11B).<ref name="cutler-interview" /> RSX-11B then evolved into the fully fledged RSX-11D disk-based operating system, which first appeared on the [[PDP-11/40]] and [[PDP-11/45]] in early 1973.<ref name=DEChist75>{{cite book
|title=DIGITAL EQUIPMENT CORPORATION - Nineteen Fifty-Seven To The Present
|url=http://s3data.computerhistory.org/pdp-1/dec.digital_1957_to_the_present_(1978).1957-1978.102630349.pdf
|date=1975 |publisher=Digital Equipment Corporation}}</ref> The project leader for RSX-11D up to version 4 was [[Henry Krejci]].

While RSX-11D was being completed, Digital set out to adapt it for a small [[memory footprint]], giving birth to RSX-11M, first released in 1973. From 1971<ref name="NT_Introduction">{{cite web
   |url=http://tech-insider.org/windows/research/1992/11.html
   |title=Foreword to Inside Windows NT, by Helen Custer
   |author=David Cutler  |date=1993  |access-date=4 December 2017}}</ref> to 1976, the RSX-11M project was spearheaded by noted operating system designer [[Dave Cutler]], then at his first project.<ref name="NT_Introduction" /> Principles first tried in RSX-11M appear also in later designs led by Cutler, DEC's [[OpenVMS|VMS]] and [[DEC MICA|MICA]] and Microsoft's [[Windows NT]].<ref name="Russinovich">{{cite web
|url=http://www.itprotoday.com/management-mobility/windows-nt-and-vms-rest-story
|title=Windows NT and VMS: The Rest of the Story
|author=Mark Russinovich  |date=30 November 1998 |access-date=4 December 2017  |author-link=Mark Russinovich}}</ref><ref name="NT_lineage">While Windows NT system is in some areas a conceptual descendant of RSX-11M and VMS, its architecture descends directly from the [[DEC MICA|MICA]] operating system, which Cutler developed for the unreleased [[DEC PRISM|PRISM]] processor. See: {{cite web
   |url=http://www.bitsavers.org/pdf/dec/prism/memos/880610_OSF_on_PRISM.pdf
   |title=Internal Memo  |publisher=Digital Equipment Corporation |date=10 June 1988
   |access-date=4 December 2017}}</ref><ref>"RSX was a separate path at DEC and the progenitor more than anything of VMS that went to NT via Dave Cutler." — [[Gordon Bell]],  Vice President, Research and Development, Digital Equipment Corporation.</ref>

Under the direction of [[Ron McLean (computer scientist)|Ron McLean]] a derivative of RSX-11M, called RSX-20F, was developed to run on the PDP-11/40 front-end processor for the KL10 [[PDP-10]] CPU.<ref name=RSX20F.KL>{{cite web
|url=http://www.bitsavers.org/pdf/dec/pdp10/TOPS20/AA-H352B-TK_RSX-20F_Nov81.pdf
|title=TOPS-10/TOPS-20 RSX-20F System Reference Manual
|page=1{{hyphen}}6 |quote=For these reasons, RSX-11M was chosen as the basis for RSX-20F. |date=November 1980}}</ref>

Meanwhile, RSX-11D saw further developments: under the direction of [[Garth Wolfendale]] (project leader 1972–1976) the system was redesigned and saw its first commercial release. Support for the 22-bit PDP-11/70 system was added. Wolfendale, originally from the UK,  also set up the team that designed and prototyped the [[Interactive Application System]] (IAS)<ref name=DEChist75/> operating system in the UK; IAS was a variant of RSX-11D more suitable for [[time sharing]]. Later development and release of IAS was led  by [[Andy Wilson (computer scientist)|Andy Wilson]], in Digital's UK facilities.