Editing PDP-11 (section)

== Decline ==
The basic design of the PDP–11 was flexible, and was continually updated to use newer technologies. However, the limited [[throughput]] of the Unibus and [[Q-Bus]] started to become a system-performance [[wikt:bottleneck|bottleneck]], and the 16-bit logical address limitation hampered the development of larger software applications. The article on [[PDP-11 architecture#Memory expansion|PDP–11 architecture]] describes the hardware and software techniques used to work around address-space limitations.

DEC's 32-bit successor to the PDP–11, the [[VAX|VAX–11]] (for "Virtual Address eXtension") overcame the 16-bit limitation, but was initially a [[superminicomputer]] aimed at the high-end [[time-sharing]] market. The early VAX CPUs provided a PDP–11 [[compatibility mode]] under which much existing software could be immediately used, in parallel with newer 32-bit software, but this capability was dropped with the first [[MicroVAX]].

For a decade, the PDP–11 was the smallest system that could run [[Unix]],<ref name="fiedler198310">{{cite news | url=https://archive.org/stream/byte-magazine-1983-10/1983_10_BYTE_08-10_UNIX#page/n133/mode/2up | title=The Unix Tutorial / Part 3: Unix in the Microcomputer Marketplace | work=BYTE | date=October 1983 | access-date=30 January 2015 | author=Fiedler, Ryan | pages=132}}</ref> but in the 1980s, the [[IBM Personal Computer|IBM PC]] and its clones largely took over the small computer market; ''[[Byte (magazine)|BYTE]]'' in 1984 reported that the PC's [[Intel 8088]] microprocessor could outperform the PDP–11/23 when running Unix.{{r|hinnant198408}} Newer microprocessors such as the [[Motorola 68000]] (1979) and [[Intel 80386]] (1985) also included 32-bit logical addressing. The 68000 in particular facilitated the emergence of a market of increasingly powerful scientific and technical [[workstation]]s that would often run Unix variants. These included the [[HP 9000]] series 200 (starting with the HP 9826A in 1981) and 300/400, with the [[HP-UX]] system being ported to the 68000 in 1984; [[Sun Microsystems]] workstations running [[SunOS]], starting with the [[Sun-1]] in 1982; [[Apollo/Domain]] workstations starting with the DN100 in 1981 running [[Domain/OS]], which was proprietary but offered a degree of Unix compatibility; and the [[Silicon Graphics]] [[SGI IRIS|IRIS]] range, which developed into Unix-based workstations by 1985 (IRIS 2000).

Personal computers based on the 68000 such as the [[Apple Lisa]] and [[Mac (computer)|Macintosh]], the [[Atari ST]], and the [[Amiga|Commodore Amiga]] arguably constituted less of a threat to DEC's business, although technically these systems could also run Unix derivatives. In the early years, in particular, [[Microsoft]]'s [[Xenix]] was ported to systems like the [[TRS-80 Model II#Model 16|TRS-80 Model 16]] (with up to 1 MB of memory) in 1983, and to the Apple Lisa, with up to 2 MB of installed RAM, in 1984. The mass-production of those chips eliminated any cost advantage for the 16-bit PDP–11. A line of personal computers based on the PDP–11, the [[DEC Professional (computer)|DEC Professional]] series, failed commercially, along with other non-PDP–11 PC offerings from DEC.

In 1994, DEC<ref>{{cite newsgroup|url=https://groups.google.com/d/msg/biz.digital.announce/mnNlxqdYTwo/Bh84UGO09kEJ|newsgroup=biz.digital.announce|title=Press/Digital and Mentec Announce PDP-11 Software Agreement|date=June 29, 1994|access-date=September 25, 2020|archive-date=July 1, 2024|archive-url=https://web.archive.org/web/20240701172334/https://groups.google.com/g/biz.digital.announce/c/mnNlxqdYTwo/m/Bh84UGO09kEJ|url-status=live}}</ref> sold the PDP–11 system-software rights to [[Mentec|Mentec Inc.]], an Irish producer of LSI-11 based boards for Q-Bus and ISA architecture personal computers, and in 1997 discontinued PDP–11 production. For several years, Mentec produced new PDP–11 processors. Other companies found a [[niche market]] for replacements for legacy PDP–11 processors, disk subsystems, etc. At the same time, free implementations of Unix for the PC based on [[BSD]] or [[Linux]] became available.

By the late 1990s, not only DEC but most of the New England computer industry which had been built around minicomputers similar to the PDP–11 collapsed in the face of microcomputer-based workstations and servers.