View source for PDP-9

{{Infobox Machine
| name = PDP-9
| image = CIPG-PDP9.png
| imgwidth = 200px
| caption = PDP-9 at MIT Cognitive Information Processing Group
| manufacturer = [[Digital Equipment Corporation]]
| year first shipped = 1966
| form factor = [[minicomputer]]
| word size = 18 bits
| physical address = 15 bits (32K words)
| virtual address = 13 bits (direct), 15 bits (extended)
| logic type = PNP [[Transistor]] [[FLIP CHIP]]s
| design type = [[microcode]]d
<!-- | clock speed =  μsec (basic instructions) -->
| memory speed = 1 μsec (9) or 1.5 μsec (9/L)
| memory mgmt = bounds register
<!-- | operating system = -->
| predecessor = [[PDP-7]]
| successor = [[PDP-15]]
| price = US$30K (8KW system)
}}
The '''PDP-9''' was [[Digital Equipment Corporation|DEC]]'s fourth 18-bit computer, and the first DEC [[Central Processing Unit|CPU]] to use [[microcode]]. A little over 400 were built. It was basically a re-implementation of the [[PDP-7]] (built out of [[System Module]]s) in [[FLIP CHIP]]s; the PDP-9 'Basic Software System' manual indicates that most PDP-7 software will run, un-modified.

Its principal intended use was for [[real-time system]]s, including data recording and process control. A variety of models were offered; the basic system provided 8K words of [[main memory]], and the PDP-9/L was a cost-reduced system with cheaper peripherals and 4KW of memory.

==Internals==

It was a [[load-store architecture]], with a single [[accumulator]]. [[Instruction]]s had a 4-bit [[operation code|opcode]], 1 bit of indirect, and 13 bits of [[address]]. Opcodes 000-060 were memory-reference instructions; for non-memory operations ('074' opcode), and [[input/output|I/O]] ('070'), bits in the 'address' field were used to specify details. '064' opcodes were for the optional [[Extended Arithmetic Element|EAE]].

For the high-speed [[read-only memory|ROM]] needed for a microcoded design, it used read-only hard-wired [[core memory]], similar to that in the [[Apollo Guidance Computer]]. [[Microinstruction]]s were 36 bits wide, of which 6 were the 'control memory address' (CMA), the address of the next one; there was no micro-[[Program Counter|PC]]. Conditional micro-branching was available by modifying the CMA during that microinstruction. Some [[front panel]] functions (START, EXAMINE/DEPOSIT (NEXT), and READ IN) are implemented with microcode.  According to a comment in the PDP-11 FAQ from Bernd Ullman, "''the first intention was to build a horizontally programmed machine but this was dropped because of the resulting word length needed for the control-words. So some(most ?) of the control signals were encoded and this led to a typical diagonally microprogrammed machine I think.''"

Multiply/divide was a hardware option, the KE09A EAE, which also performed shifting; it was installed in pre-wired slots in the CPU's [[backplane]]. Use of more than 8KW of main memory (all core in the PDP-9) required the Memory Extension Control, KG09A, which provided [[bank switching]]. A [[memory management]] option, the KX09A, was also available; it included a [[register]] to set the boundary between protected and un-protected memory, and two modes for the CPU.

The KF09A Automatic Priority Interrupt option provided 8 levels of [[interrupt]] priority, each of which could support up to 8 [[peripheral|devices]]. Each device could provide its own [[interrupt vector]]. The DM09 [[Direct Memory Access]] Channel Multiplexor Adapter provided high-speed devices with direct access to main memory for data transfers.

A large range of [[peripheral]]s were available, including [[DECtape]] (via the TC02 controller), [[magnetic tape]] (via the TC59), [[drum]] (RM09 controller) and [[fixed-head disk]] (RB09; and RS09, via the RF09 controller). The RM09 and RB09 use the DM09.

{{semi-stub}}

==See also==

* [[PDP-9 control memory]]

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==Further reading==

''(All available online through [[BitSavers]].)''
-->
==External links==

* [http://www.bitsavers.org/pdf/dec/pdp9/ PDP-9] - documentation at [[BitSavers]]; has manuals for KE09, KG09, KX09, KF09, etc
** [http://www.bitsavers.org/pdf/dec/pdp9/PDP-9_UsersManual.pdf PDP-9 User Handbook]
** [http://www.bitsavers.org/pdf/dec/pdp9/DEC-09-I3CA-D-68.pdf TC02 DECtape Transport Control Instruction Manual]
** [http://www.bitsavers.org/pdf/dec/pdp9/DEC-09-I3CA-D-69.pdf TC02 DECtape Control Maintenance Manual]
* [https://bitsavers.org/pdf/dartmouth/theses/Blean_-_The_PDP-9_Mini_Time-Sharing_System_197206.pdf Dartmouth PDP-9 Mini Time-Sharing System]
* [https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-9 DEC PDP-9 System Number 319] - the RICM's PDP-9 - has lots of good images of the interior
** [https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration DEC PDP-9 Restoration] - the start of a long saga - 2012-17
** [https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration-blog-starting-2019 PDP-9 Restoration Blog Starting 2019]
** [https://www.ricomputermuseum.org/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration-blog-starting-2020 PDP-9 Restoration Blog Starting 2020]
** [https://sites.google.com/a/ricomputermuseum.org/home/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration-blog-starting-2021 PDP-9 Restoration Blog Starting 2021]
** [https://sites.google.com/a/ricomputermuseum.org/home/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration-blog-starting-2022 PDP-9 Restoration Blog 2022]
** [https://sites.google.com/a/ricomputermuseum.org/home/collections-gallery/equipment/dec-pdp-9/pdp-9-restoration-blog-starting-2023 PDP-9 Restoration Blog 2023]
* [https://www.pdp-9.net/start-page Digital Equipment Corp. PDP-9] - another PDP-9
** [https://www.pdp-9.net/restoration-blog/the-rescue The rescue]

{{Nav DEC}}

[[Category: DEC Systems]]
[[Category: 18-bit Computers]]