Megabyte was used to describe the 22-bit addressing of DEC PDP-11 / 70 ( 1975 )

The effort was sufficiently complete that during the summer of 1973 the Unix kernel for the PDP-11 was rewritten in C. During the 1972 – 73 period there was a need to port to Honeywell 635 and IBM 360 / 370 machines, so Mike Lesk wrote the " portable I / O package " which would become the C " standard I / O " routines.

Many more machines offered user-programmable writable control stores as an option ( including the HP 2100, DEC PDP-11 / 60 and Varian Data Machines V-70 series minicomputers ).

Implementations also exist for the Interdata 8 / 32, PDP-11, VAX, Alpha platforms and HP Integrity servers ; for the Honeywell, and for the Computer Technology Limited ( CTL, later ITL ) Modular-1 ; as well as for SPARC running Solaris and Intel running Linux.

* PDP-11 CORAL / ASM interfacing library

Examples of CISC instruction set architectures are System / 360 through z / Architecture, PDP-11, VAX, Motorola 68k, and x86.

Digital Equipment Corporation should not be confused with the unrelated companies Digital Research, Inc or Western Digital ( despite the latter manufacturing the LSI-11 chipsets used in DEC's low end PDP-11 / 03 computers ).

The PDP-11 supported several operating systems, including Bell Labs ' new Unix operating system as well as DEC's DOS-11, RSX-11, IAS, RT-11, DSM-11, and RSTS / E.

Large numbers of PDP-11 / 70s were deployed in telecommunications and industrial control applications.

ed was originally written in PDP-11 / 20 assembler by Ken Thompson in 1971.

The most significant were Digital Equipment Corporation with DSM ( Digital Standard MUMPS ), InterSystems with ISM ( InterSystems M ) on VMS and UNIX, and M / 11 + on the PDP-11 platform.

* The Digital Equipment Corporation PDP-11 processors, with the exception of the PDP-11 / 20, were microprogrammed.

KL10 frontend PDP-11 / 40

The KL class machines could not be started without the assist of a PDP-11 / 40 frontend computer installed in every system.

PDP-11 / 40

Design features of the PDP-11 influenced the design of microprocessors such as the Motorola 68000 ; design features of its operating systems, as well as other operating systems from Digital Equipment, influenced the design of other operating systems such as CP / M and hence also MS-DOS.

The first officially named version of Unix ran on the PDP-11 / 20 in 1970.

PDP-11 / 40 with TU56 dual DECtape drive.

The last models of the PDP-11 line were the PDP-11 / 94 and-11 / 93 introduced in 1990.

The PDP-11 family was extremely long-lived, spanning 20 years and many different implementations and technologies.

original PDP-11 / 20 front panel

* PDP-11 / 35 and PDP-11 / 40 — A microprogrammed successor to the PDP-11 / 20 ; the design team was led by Jim O ' Loughlin.

* PDP-11 / 05 and PDP-11 / 10 — A cost-reduced successor to the PDP-11 / 20.

* SBC 11 / 21 ( boardname KXT11 ) Falcon and Falcon Plus — single board computer on a Qbus card implementing the basic PDP-11 instruction set, based on T11 chipset containing 32 KB static RAM, two ROM sockets, three serial lines, 20 bit parallel I / O, three interval timers and a two-channel DMA controller.

When the first PDP-11 was acquired for UNIX in late 1970 ( a PDP-11 / 20 ), the justification cited to management for the funding required was that it was to be used as a word processing system, and so roff was quickly transliterated again, into PDP-11 assembly, in 1971.

In 1973 memory management support was included in RSTS ( now RSTS / E ) for the newer DEC PDP-11 / 40 and PDP-11 / 45 minicomputers ( the PDP-11 / 20 was only supported under RSTS-11 ).

The original processors were PDP-11 / 20 processors, but in the final system, only five of these were used ; the remaining 11 were PDP-11 / 40 processors, which were modified by having additional writeable microcode space.

Most of the 11 / 20 modifications were custom changes to the motherboard, but because the PDP-11 / 40 was implemented in microcode, a separate " proc-mod " board was designed that intercepted certain instructions and implemented the protected operating system requirements.

Since addressing modes 0-3 were identical, this made 13 ( electronic ) addressing modes, but as in the PDP-11, the use of the Stack Pointer ( R14 ) and Program Counter ( R15 ) created a total of over 15 conceptual addressing modes ( with the assembler program translating the source code into the actual stack-pointer or program-counter based addressing mode needed ).

* PDP-11 / 45, PDP-11 / 50, and PDP-11 / 55 — A much faster microprogrammed processor that could use up to 256 kB of semiconductor memory instead of or in addition to core memory.

* PDP-11 / 70 — The 11 / 45 architecture expanded to allow 4 MB of physical memory segregated onto a private memory bus, 2 kB of cache memory, and much faster I / O devices connected via the Massbus.

* PDP-11 / 34 and PDP-11 / 04 — Cost-reduced follow-on products to the 11 / 35 and 11 / 05 ; the PDP-11 / 34 concept was created by Bob Armstrong.

* PDP-11 / 60 — A PDP-11 with user-writable microcontrol store ; this was designed by another team led by Jim O ' Loughlin.

* PDP-11 / 44 — Replacement for the 11 / 45 and 11 / 70 that supported optional cache memory and floating-point processor, and included a sophisticated serial console interface and support for 4 MB of physical memory.

* PDP-11 / 24 — First VLSI PDP-11 for Unibus, using the " Fonz-11 " ( F11 ) chip set with a Unibus adapter.

* PDP-11 / 84 — Using the VLSI " Jaws-11 " ( J11 ) chip set with a Unibus adapter.

* PDP-11 / 94 — J11-based, faster than 11 / 84.

* PDP-11 / 03 ( also known as the LSI-11 / 03 ) — The first LSI PDP-11, this system used a chipset from Western Digital and supported 60 kB of memory.

* PDP-11 / 23 — Second generation of LSI ( F-11 ).

The PDP-11 processors tended to fall into several natural groups depending on the original design upon which they are based and which I / O bus they used.

original PDP-11 / 70 front panel

The U. S. Navy used a PDP-11 / 34 to control its Multi-station Spatial Disorientation Device, a simulator used in pilot training, until 2007, when it was replaced by a PC-based emulator that could run the original PDP-11 software and interface with custom Unibus controller cards.

As late as 1980, PDP-11 / 45 machines that used drums for swapping ( and magnetic core memory ) were still in use at many of the original UNIX sites.

V7M, developed by DEC's original Unix Engineering Group ( UEG ), contained many enhancements to the kernel for the PDP-11 line of computers including significantly improved hardware error recovery and many additional device drivers.

The original version, DIBOL-8, was produced for PDP-8, PDP-11 and DIBOL-32 VAX / VMS systems, though it can also be run on other systems through emulators.

The Whitesmiths compiler, written for the PDP-11, was released in 1978 and compiled a version of C similar to that accepted by Version 6 Unix ( Dennis Ritchie's original C compiler ).