Difference between revisions of "PDP-11/20"

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| name = PDP-11/20
 
| name = PDP-11/20
 
| manufacturer = [[Digital Equipment Corporation]]
 
| manufacturer = [[Digital Equipment Corporation]]
−
| introduced= 1970
+
| architecture        = [[PDP-11]]
−
| bus arch = [[Unibus]]
+
| year announced      = January, 1970
 +
| year design started = before January, 1969
 +
| year first shipped  = June, 1970
 +
<!-- | year discontinued  = -->
 +
| form factor        = [[Minicomputer]]
 +
| word size          = 16
 +
| physical address    = 256KB (only 56KB accessible by basic -11/20)
 +
| virtual address    = 64KB
 +
| logic type          = [[transistor-transistor logic|TTL]]
 +
| design type        = [[state machine]] (not [[microcode]]d)
 +
| clock speed        = 280 nsec
 +
<!-- | cycle time          =  CPU cycle time in ns/µs/etc -->
 +
| instruction speed  = 2.3 μsec (register-register)
 +
| memory speed        = [[MM11-E and MM1-F core memories|MM11-E]]: 500 nsec [[access time]]<br>&nbsp; &nbsp; &nbsp; 1.2 μsec [[cycle time]]
 +
| cpu                = [[KA11 CPU]]
 +
| bus arch           = [[UNIBUS]]
 +
| memory mgmt        = none standard
 +
| operating system    = [[DOS-11]], [[DOS/BATCH]], [[RSTS-11]], [[UNIX]], others
 +
| predecessor        = none
 +
| successor          = [[PDP-11/05]]
 
}}
 
}}
 +
[[Image:PDP11-20.jpg|left|200px|thumb|PDP11/20]]
 +
 +
The PDP-11/20 was the first [[PDP-11]] from [[Digital Equipment Corporation|DEC]]; its [[KA11 CPU]] was built from a set of [[DEC card form factor|quad width extended-length]] cards carrying SSI [[transistor-transistor logic|TTL]] [[integrated circuit|chips]], along with a few dual width cards. It introduced the [[UNIBUS]] as a universal path to connect together the [[Central Processing Unit|CPU]], [[main memory]] and [[peripheral|devices]].
 +
 +
It was the only PDP-11 to use discrete logic for its control circuits, as opposed to [[microcode]] (this was because the cheap, fast [[read-only memory|ROMs]] needed for economical implementation of that approach did not exist yet at the time it was designed).
 +
 +
The CPU consisted of two and a half quad [[system unit]] [[backplane]]s (the two otherwise-unused slots were [[Small Peripheral Controller|SPC]] slots, available for any [[peripheral]]) [[wire-wrap]]ped into a single unit (see [[KA11 CPU#Implementation|here]] for details). They, and the [[KY11-A Programmer's Console|KY11-A]] [[front panel]], were mounted in a [[BA11-C Mounting Box]].
 +
 +
==Extensions==
 +
 +
The -11/20 did not have, as standard capabilities, many things that eventually became included on later models, such as hardware multiply and divide, [[floating point]], and [[memory management]]. DEC provided a series of optional accessories that provided some of these capabilities.
 +
 +
One was a [[co-processor]] for the multiply/divide functions, the [[KE11-A Extended Arithmetic Element]]; rather than additional [[instruction]]s in the CPU, it was implemented as a [[peripheral|device]] on the [[bus]], making this model somewhat incompatible with the rest of the PDP-11's.
 +
 +
The [[KS11 Memory Protection and Relocation option|KS11]] was apparently DEC's first attempt at an add-on to provide memory management to the -11/20. Other than a [https://www.bell-labs.com/usr/dmr/www/odd.html funny story], little is known of it. The extremely rare [[KT11-B Paging Option]] was logically an addition to the CPU, interposed between the KA11 and the UNIBUS (but also having a few ties into the CPU); it allowed [[hardware]]-based [[time-sharing]], and use of up to the full 248 KBytes of memory addressable by the UNIBUS.
 +
 +
==Software==
 +
 +
The -11/20 was the machine that [[RSTS/E|RSTS]] (called 'RSTS-11' when it was on the -11/20) ran on. Many other DEC PDP-11 [[operating system]]d (e.g. [[DOS-11]]) started out on the -11/20.
 +
 +
It was the first PDP-11 to run [[UNIX]], albeit a very early version.
 +
 +
== hampage.hu ==
 +
Quoted:
 +
<i>
 +
The first of the -11's, born in June 1970, featuring the KA11 processor.
 +
 +
The PDP-11/20 is a general-purpose computer with a wordlength of 16 bits. It features 8 general registers, and one interconnect for all system components (CPU, memory, peripheral devices), the UNIBUS (which is not the successor of the PDP8 OMNIBUS).
 +
 +
This bus had an addressing range of 18 bits, but only 16 were used, which led to the 32 Kword (as mentioned, one word was 16 bits, so this is equal 64 Kbyte) memory limit. As with the other members of the -11 family, the top 4 KW of the memory is reserved to the system (the upper memory addresses refer to devices connected to the CPU). It is also interesting to know that most machines were shipped with only 12 KW of magnetic core memory.
 +
 +
On the picture above we can see some typical I/O devices: 4 [[ASR33]] teletype terminals and DECtape drives over the fan-fold papertape puncher/reader. The front panel had lights and switches for address and data (the lights were not LED's).
 +
 +
The original operating system was DOS/BATCH, but one of the early versions of UNIX was also developed on the /20.
 +
 +
Interesting options: MX11 - Memory Extension Option: this enabled the usage of 128 KW memory (18-bit addressing range); KS11: this option provided hardware memory protection, which the plain /20 lacked. Both options were developed by the Digital CSS (Computer Special Systems).
 +
 +
Trivia: The machine was set to be named "PDP-11/30" originally, but it was renamed to 11/20 because of the similar designation of the IBM 1130.
 +
</i>
 +
 +
==See also==
 +
 +
* [[KS11 Memory Protection and Relocation option]]
 +
 +
==External links==
 +
 +
* [https://vintagecomputer.net/digital/PDP11-20/PDP11_Price-List_19691215.pdf pdp11 price list] (December 15, 1969) - pre-production price list, includes the 'PDP-11/10'
 +
* [http://www.bitsavers.org/pdf/dec/pdp11/1120/PDP11-20_Price_List_19701101.pdf pdp11/20 Price List] (November 1, 1970)
 +
* [http://www.bitsavers.org/pdf/dec/pdp11/1120/ 11/20] - documentation at [[Bitsavers]]
 +
** [http://www.bitsavers.org/pdf/dec/pdp11/1120/1120_SystemManual.pdf PDP-11/20 system manual] (DEC-11-HR1B-D)
 +
** [http://www.bitsavers.org/pdf/dec/pdp11/1120/1120_SystemSchems_Feb70.pdf PDP-11/20 Engineering Drawings]
 +
* [http://gordonbell.azurewebsites.net/Digital/PDP%2011%20Handbook%201969.pdf pdp11 handbook] - PDP-11/20 Processor Handbook
 +
* [https://vintagecomputer.net/digital/PDP11-20/PDP11_Brochure_1970Feb.pdf pdp11] - DEC brochure
 +
* [https://vintagecomputer.net/digital/PDP11-20/PDP11_Articles_1970Jan.pdf PDP-11 rides on a unibus] - announcement press coverage
 +
* [http://hampage.hu/pdp-11/1120.html PDP-11/20, /15]
  
 
{{PDP-11}}
 
{{PDP-11}}
  
−
[[Category:DEC processors]][[Category:UNIBUS processors]]
+
[[Category: UNIBUS PDP-11s]]

Latest revision as of 22:22, 11 October 2024


PDP-11/20
Manufacturer: Digital Equipment Corporation
Architecture: PDP-11
Year Announced: January, 1970
Year Design Started: before January, 1969
Year First Shipped: June, 1970
Form Factor: Minicomputer
Word Size: 16
Logic Type: TTL
Design Type: state machine (not microcoded)
Clock Speed: 280 nsec
Instruction Speed: 2.3 μsec (register-register)
Memory Speed: MM11-E: 500 nsec access time
      1.2 μsec cycle time
CPU: KA11 CPU
Physical Address Size: 256KB (only 56KB accessible by basic -11/20)
Virtual Address Size: 64KB
Memory Management: none standard
Bus Architecture: UNIBUS
Operating System: DOS-11, DOS/BATCH, RSTS-11, UNIX, others
Predecessor(s): none
Successor(s): PDP-11/05
PDP11/20

The PDP-11/20 was the first PDP-11 from DEC; its KA11 CPU was built from a set of quad width extended-length cards carrying SSI TTL chips, along with a few dual width cards. It introduced the UNIBUS as a universal path to connect together the CPU, main memory and devices.

It was the only PDP-11 to use discrete logic for its control circuits, as opposed to microcode (this was because the cheap, fast ROMs needed for economical implementation of that approach did not exist yet at the time it was designed).

The CPU consisted of two and a half quad system unit backplanes (the two otherwise-unused slots were SPC slots, available for any peripheral) wire-wrapped into a single unit (see here for details). They, and the KY11-A front panel, were mounted in a BA11-C Mounting Box.

Extensions

The -11/20 did not have, as standard capabilities, many things that eventually became included on later models, such as hardware multiply and divide, floating point, and memory management. DEC provided a series of optional accessories that provided some of these capabilities.

One was a co-processor for the multiply/divide functions, the KE11-A Extended Arithmetic Element; rather than additional instructions in the CPU, it was implemented as a device on the bus, making this model somewhat incompatible with the rest of the PDP-11's.

The KS11 was apparently DEC's first attempt at an add-on to provide memory management to the -11/20. Other than a funny story, little is known of it. The extremely rare KT11-B Paging Option was logically an addition to the CPU, interposed between the KA11 and the UNIBUS (but also having a few ties into the CPU); it allowed hardware-based time-sharing, and use of up to the full 248 KBytes of memory addressable by the UNIBUS.

Software

The -11/20 was the machine that RSTS (called 'RSTS-11' when it was on the -11/20) ran on. Many other DEC PDP-11 operating systemd (e.g. DOS-11) started out on the -11/20.

It was the first PDP-11 to run UNIX, albeit a very early version.

hampage.hu

Quoted: The first of the -11's, born in June 1970, featuring the KA11 processor.

The PDP-11/20 is a general-purpose computer with a wordlength of 16 bits. It features 8 general registers, and one interconnect for all system components (CPU, memory, peripheral devices), the UNIBUS (which is not the successor of the PDP8 OMNIBUS).

This bus had an addressing range of 18 bits, but only 16 were used, which led to the 32 Kword (as mentioned, one word was 16 bits, so this is equal 64 Kbyte) memory limit. As with the other members of the -11 family, the top 4 KW of the memory is reserved to the system (the upper memory addresses refer to devices connected to the CPU). It is also interesting to know that most machines were shipped with only 12 KW of magnetic core memory.

On the picture above we can see some typical I/O devices: 4 ASR33 teletype terminals and DECtape drives over the fan-fold papertape puncher/reader. The front panel had lights and switches for address and data (the lights were not LED's).

The original operating system was DOS/BATCH, but one of the early versions of UNIX was also developed on the /20.

Interesting options: MX11 - Memory Extension Option: this enabled the usage of 128 KW memory (18-bit addressing range); KS11: this option provided hardware memory protection, which the plain /20 lacked. Both options were developed by the Digital CSS (Computer Special Systems).

Trivia: The machine was set to be named "PDP-11/30" originally, but it was renamed to 11/20 because of the similar designation of the IBM 1130.

See also

External links


v • d • e PDP-11 Computers and Peripherals
UNIBUS PDP-11s - PDP-11/20 • PDP-11/15 • PDP-11/35 • PDP-11/40 • PDP-11/45 • PDP-11/50 • PDP-11/55 • PDP-11/70
PDP-11/05 • PDP-11/10 • PDP-11/04 • PDP-11/34 • PDP-11/60 • PDP-11/44 • PDP-11/24 • PDP-11/84 • PDP-11/94

QBUS PDP-11s - PDP-11/03 • PDP-11/23 • PDP-11/23+ • MicroPDP-11/73 • MicroPDP-11/53 • MicroPDP-11/83 • MicroPDP-11/93

QBUS CPUs: LSI-11 • LSI-11/2 • KDF11-A • KDF11-B • KDJ11-A • KDJ11-B • KDJ11-D • KDJ11-E

Buses: UNIBUS • UNIBUS map • SPC • MUD • EUB • QBUS • CD interconnect • PMI

Also: PDP-11 architecture • PDP-11 Extended Instruction Set • FP11 floating point • PDP-11 Memory Management

UNIBUS CPUs: KA11 • KC11 • KB11-A • KB11-B • KB11-C • KB11-D • KD11-A • KD11-B • KD11-D • KD11-E • KD11-EA • KD11-K • KD11-Z • KDF11-U

Co-processors: FP11-A • FP11-B • FP11-C • FP11-E • FP11-F • KE44-A • FPF11

Chips: LSI-11 • KEV11-A • KEV11-B • KEV11-C • F-11 • KEF11-A • KTF11-A • T-11 • J-11 • FPJ11

CPU options: KE11-E • KE11-F • KJ11-A • KT11-C • KT11-D • KK11-A • KK11-B • KT24 • KTJ11-B

Rare CPU options: KS11 Memory Protection and Relocation option • KT11-B Paging Option • KUV11 Writeable Control Store

Front panels: KY11-A • KY11-D • KY11-J • KY11-LA • KY11-LB • KY11-P

More on buses: UNIBUS and QBUS termination • Bus Arbitration on the Unibus and QBUS • CTI BUS

PDT-11s - PDT-11/110 • PDT-11/130 • PDT-11/150   CTI PDP-11s - PRO-325 • PRO-350 • PRO-380

Clones: CM 1420 • SM 1420

Other: FIS floating point • PDP-11 Commercial Instruction Set • PDP-11 stacks • PDP-11 family differences

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