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'''Pascal MicroEngine''' is a series of [[microcomputer]] products manufactured by [[Western Digital]] from 1979 through the mid-1980s, designed specifically to run the [[UCSD p-System]] efficiently.<ref>[https://books.google.com/books?id=IT4EAAAAMBAJ&dq=Pascal+MicroEngine&pg=PA2 Pascal "Cast in silicon" By Western Digital], InfoWorld, 11 Dec 1978, Page 2, ''...under the trademarked name "Pascal Microengine," will be priced at $2995...First units are expected to be available in January, 1979...''</ref> Compared to other microcomputers, which use a [[machine language]] [[p-code machine|p-code]] [[Interpreter (computing)|interpreter]], the Pascal MicroEngine has its interpreter implemented in [[microcode]]; p-code is its machine language. The most common [[programming language]] used on the p-System is [[Pascal (programming language)|Pascal]].

The MicroEngine runs a special release III p-System. The enhancements of release III were incorporated into release IV which was made publicly available for other platforms but not for the MicroEngine.


==Products==
The MicroEngine series of products was offered at various levels of integration:

* WD-9000 five chip [[microprocessor]] chip set<ref>[https://books.google.com/books?id=mT4EAAAAMBAJ&dq=western+digital+MicroEngine&pg=PT33 Advert: ACI-90(tm) Pascal Computer System], InfoWorld, 24 Nov 1980, Page 34, ''...Microengine(tm) Equipped..the Western Digital's WD/9000 Pascal Microengine(tm)...''</ref><ref>[https://books.google.com/books?id=LD4EAAAAMBAJ&dq=Pascal+MicroEngine&pg=PA15 Turnkey Pascal Business System], InfoWorld, 21 Nov 1979, Page 15, ''...The ACI-90(tm), a 16-bit Pascal computer system equipped with Western Digital's Microengine(tm)...''</ref>
* WD-900 single board computer
* WD-90 packaged system
* SB-1600 MicroEngine single board computer
* ME-1600 Modular MicroEngine packaged system

The MicroEngine chipset was based on the [[MCP-1600]] chipset, which formed the basis of the [[Digital Equipment Corporation|DEC]] [[LSI-11]] low-end [[minicomputer]] and the [[Western Digital WD16|WD16]] processor used by [[Alpha Microsystems]] (each using different microcode).

One of the well regarded systems was the [[S-100 bus]] based dual processor cards developed by Digicomp Research of Ithaca, NY.<ref>[https://books.google.com/books?id=Tz4EAAAAMBAJ&dq=Pascal+MicroEngine&pg=PT18 Hardware/Briefs], InfoWorld, 7 Jul 1980, Page 19, ''...Digicomp Research Corporation has announced '''Pascal-100''', a '''Pascal CPU for the S-100 bus'''. Based on the Western Digital Pascal Microengine..''</ref> These cards deserve an entry on their own, as they survived the demise of the WD single-board system and delivered reliable performance at up to 2.5[[Mhz]]. A typical configuration was a Digicomp [[Central processing unit|dual processor]] board set, containing a [[Zilog Z80]] and a [[Bipolar junction transistor|bipolar]] memory mapper harnessed to a microengine chipset on the second board, linked by a direct cable. The sole configuration known to be still running in 2018 and documented on the web is described by Marcus Wigan<ref name="mwigan.7">{{cite web | url = http://mwigan.com/mrw/8-wd-microengine.html | title = Western Digital Pascal Microengine-Based Systems | author = Marcus Wigan | date = 2015-02-02 | accessdate = 2016-10-09 }}</ref> and contains 312 [[kilobyte|kB]] of memory, [[RAM disk|RAM disc]] support through a modified Z80 BIOS (written by Tom Evans) taking advantage of the [[virtual memory|memory mapping]] chip on the Z80 board, and using the UCSD Pascal III version of the [[operating system]] tuned specifically for the WD chipset - once the Microengine had booted the ram-disc was available. A software facility within UCSD Pascal allowed the system to copy the entire operating system to the ram disc and transfer control to it. This sped it up remarkably. This use of a Z80 [[BIOS]] to handle all the devices, allowed the use of a range of [[floppy discs]], I/O boards and [[Disk controller|hard disk controllers]].

The performance of this Microengine on a series of simply Interface Age benchmarks (originally designed for BASIC programs) is documented in an [[Australia]]n Computer Society, MICSIG, paper presented at the National Conference on Microcomputer Software, [[Canberra]], ACT presented in June 1982, <ref>{{cite journal |last1=Wigan |first1=M. R. |title=BASIC, FORTRAN, S-ALGOL, and Pascal Benchmarks on microcomputers, including the effects of floating point processor support |journal=Proceedings: National Conference on microcomputer software, Microprocessor Special Interest Group, Australian Computer Society. MICSIG, Canberra |date=August 1982 |url=https://web.archive.org/web/20120328125527if_/http://www.mwigan.com/mrw/WD_MicroEngine_files/82%20MICSIG%20ACS1-25.pdf |access-date=29 May 2025}}</ref> along with a wide range of other contemporary machines and compilers, including Z80 systems supported by the 9511 APU chip hosted in the Digicomp S-100 Microengine system that he used.

==Reception==
At the time of introduction, the only competitors were 8-bit processors (mainly [[Intel 8080]], Z80, and [[MOS Technology 6502]] based systems).{{vague|date=October 2010}} The MicroEngine could [[Compiler|compile]] Pascal [[source code]] in a fraction of the time (typically about 1/10) required by contemporaries. Fast compilation made the MicroEngine especially nice as a developer's machine, and the inclusion of a [[Semaphore (programming)|semaphore]] primitive in the microcode was particularly useful for multi user enhancements, which were developed in [[Melbourne]] for the Canberra Australia-based Ortex Company, extended to be a multiuser system and often sold with a bundled pharmacy management system, also delivered on the Sage IV computers under UCSD Pascal IV and enabled as a multiuser system using the Sage multiuser BIOS rather than by extending UCSD Pascal IV to add a semaphore. This performance advantage was eroded by the later availability of p-code to native machine code translators, and mainstream 16-bit microprocessors such as the [[Intel 8086]] and [[Motorola 68000]].

When details of the MicroEngine were first released, the system accumulated a very large number of pre-orders (for the time). The first boards shipped were poorly designed (power and ground traces the same size as [[signal trace]]s, very few [[capacitors]]), required a large number of modifications, and even then did not work reliably.{{Citation needed|date=December 2007}} A couple of years would pass after introduction before a well-engineered MicroEngine was available. Between a damaged reputation and the introduction of the [[IBM Personal Computer|IBM PC]], in the end the MicroEngine was only modestly successful.

A further example of a commercial product based on the MicroEngine was the AVAB Viking lighting control system, which used the Modular MicroEngine boards along with some custom hardware.

==Other languages==
A group led by David A. Fisher developed the third validated [[Ada (programming language)|Ada]] compiler using the Modular MicroEngine.
for version 17.1 of the Ada verification system then in use.
This compiler was later transferred to mainframe/minicomputers under the name of GenSoft Ada, and ran in an emulator of the Microengine under the MicroEngine-specific UCSD 3 operating system. Copies of the Prime computer version are known to be held by M R Wigan, who also holds a zero price licence for the full MicroEngine Ada system and UCSD 3 Operating system used for the Modular Microengine, as well as the three Modular MicroEngines used to create the 17.1 Ada, and all the development 8" floppy discs.

Ada was the only other full programming language available.<ref name="refman">. The March 1979 Preliminary Edition of the reference manual stated that a [[BASIC]] compiler was available for the system, but it is unknown if this compiler ever actually shipped.</ref>
John Lloyd of the University of Melbourne created an early version of his Prolog for this system and both Basic and Fortran 77 compilers were ported from other UCSD P-system implementations at various times, but not widely distributed.

Due to limited memory (62K 16-bit [[word (computer architecture)|words]], the last 2K words being reserved for [[memory-mapped I/O]] and [[Programmable read-only memory|PROM]] for the hard disk [[Bootstrapping (computing)|bootstrap]] code) only very small Ada programs could be compiled. At one point in the compilation the compiler [[memory paging|swapped]] the operating system out to disk, to gain just a little more room.

"A(da" replaced "A(ssmble" 
on the main command menu. No native assembler was available or needed. This UCSD-based Ada was later redeveloped for the Sage 4 by [[TeleSoft]] in San Diego.


==See also==
*[[p-code machine]]

==References==
{{Reflist|30em}}
* [https://books.google.com/books?id=s4Po-oIhNpsC&dq=Pascal+MicroEngine&pg=RA1-PA76 Based on Pascal Microengine: Desktop Graphics System Debuts], Computerworld, 14 Jul 1980, Page 76, ''...The self-contained Ensemble 120GX graphics system from Integrated Research and Information Systems is based on the Western Digital Corp. Pascal Microengine...''

==External links==
*[https://web.archive.org/web/20140725075118/http://machine-room.bedroomlan.org/computers/companies/303/ Western Digital Pascal MicroEngine]
*[http://www.bitsavers.org/pdf/westernDigital/WD90_Pascal_Microengine/ Pascal Microengine documentation] at bitsavers.org
*[https://web.archive.org/web/20120328125418/http://www.mwigan.com/mrw/WD_MicroEngine.html Western Digital Pascal Microengine-Based Systems] at www.mwigan.com

{{Pascal programming language family}}
{{Western Digital}}

{{DEFAULTSORT:Pascal Microengine}}
[[Category:Microcomputers]]
[[Category:Computer-related introductions in 1979]]
[[Category:High-level language computer architecture]]
[[Category:16-bit computers]]
[[Category:Western Digital products]]

Pascal MicroEngine - Revision history

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