Editing PDP-11 (section)

=== Models that were planned but never introduced ===
* PDP–11/74 – A PDP–11/70 that was extended to contain multiprocessing features. Up to four processors could be interconnected, although the physical cable management became unwieldy. Another variation on the 11/74 contained both the multiprocessing features and the Commercial Instruction Set. A substantial number of prototype 11/74s (of various types) were built and at least two multiprocessor systems were sent to customers for beta testing, but no systems were ever officially sold. A four processor system was maintained by the RSX-11 operating system development team for testing and a [[uniprocessor]] system served PDP–11 engineering for general purpose timesharing. The 11/74 was due to be introduced around the same time as the announcement of the new 32-bit product line and the first model: the VAX 11/780. The 11/74 was cancelled because of concern for its field maintainability,<ref>{{cite web|title=Multiprocessor FAQ|year=2005|publisher=Machine Intelligence|author1=Bruce Mitchell|author2=Brian S. McCarthy|url=http://www.miim.com/faq/hardware/multipro.shtml|access-date=August 20, 2019}}{{Dead link|date=March 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> though employees believed the real reason was that it outperformed the 11/780<ref>{{cite mailing list|url=http://www.classiccmp.org/pipermail/cctech/2006-February/057197.html|title=Original 11/74 front panel|author=Don North|date=February 7, 2006|mailing-list=cctech|archive-url=https://web.archive.org/web/20110718232453/http://www.classiccmp.org/pipermail/cctech/2006-February/057197.html|archive-date=July 18, 2011|access-date=March 15, 2007|url-status=dead}}</ref> and would inhibit its sales. In any case, DEC never entirely migrated its PDP–11 customer base to the VAX. The primary reason was not performance, but the PDP–11's superior real-time responsiveness.{{citation needed|date=May 2011}}
* PDP–11/27 – A Jaws-11 implementation that would have used the [[VAXBI Bus]] as its principal I/O bus.
* PDP–11/68 – A follow-on to the PDP–11/60 that would have supported 4&nbsp;MB of physical memory.

[[File:GT40 Lunar Lander.jpg|thumb|DEC GT40 running ''[[Lunar Lander (video game genre)|Moonlander]]''|229x229px]]