Thoth is areal-time,message passingoperating system (OS) developed at theUniversity of Waterloo inWaterloo, OntarioCanada.

Thoth was developed at theUniversity of Waterloo inWaterloo, Ontario,Canada. The curriculum at Waterloo includes aReal Time Operating Systems course and an associated "Train lab", where students must develop areal-time operating system (RTOS) to control a model track with multiple trains.^[1][2][3]

In 1972, theB programming language, a derivative ofBCPL, was brought to Waterloo byStephen C. Johnson while on sabbatical fromBell Labs.^[4] A new language derived from B, namedEh, was developed at Waterloo. Thoth was written originally in Eh with someassembly language.^[5][6]

Initial development of Thoth occurred on aHoneywell 6050 computer.^[7] It was first run on aData General Nova 2 in May 1976, and was nextported to aTexas Instruments TI990/10 in August 1976.^[7][5]

In October 1976, the University of Waterloo published Laurence S. Melen's Master's Thesis, titled "A Portable Real-Time Executive, Thoth".^[8]

Eh was later upgraded, in part with the addition ofdata types, and renamedZed. Thoth was then rewritten in Zed.^{[9][10][11][12][13]}

One of the early principal developers of Thoth wasDavid Cheriton. Cheriton would go on to develop the Verexkernel, and theV-System OS; both influenced by Thoth. Another early developer was Michael Malcolm, who would later found Waterloo Microsystems,Network Appliances, Inc.,Blue Coat Systems, and Kaliedescape, several of whose operating systems are believed to have been derived from or influenced by Thoth.

Certain papers describe DEMOS as the inspiration for Thoth.^[14] As prior art Cheriton citedPer Brinch Hansen'sRC 4000, then listed Thoth, DEMOS, and Accent together as later developments.^[15] Other influences on the development of Thoth includedMultics,Data General's RTOS,Honeywell GCLS, andUnix.^[5] Later references cite Thoth as the original implementation of its particular use of synchronous message passing and multiprocess program structure, which were subsequently applied by other projects.^[16]: 2

Work on Thoth ended around 1982.^[17]

Thoth was developed to meet four goals:^[7]

1. Easily portable to other hardware^[3]
2. Programs run as a set of inexpensive, cooperatingconcurrent processes with efficientinter-process communications (IPC)^[5]
3. Suitable for real-time uses as to system response to external events
4. Adaptable and scalable to a wide range of real-time uses

Thoth exposes the sameabstract machine toapplication software, regardless of the underlyingphysical machine.^[5][18] This abstract machine was defined with certain minimal requirements, such that meeting these requirements allowed a given computer to be included in theThoth Domain of potential Thoth port targets.

Processes running under Thoth can be grouped into "Teams". All processes within a team share a common address space and can share data.^[19][7] This is similar to other systems' concepts of "lightweight processes" or threads.^[20] Processes not members of the same team communicate using Thoth's IPC.

Inter Process Communication in Thoth is primarily accomplished by means of synchronous message passing.^[7] This approach greatly simplified message queueing.^[21]

Although the term was not current when the original papers were written, Thoth has been called amicrokernel.^[22][20][23]

Thoth's synchronous message passing IPC lent itself to the application of an anthropomorphic programming model, building on the work ofCarl Hewitt'sactor model, and ofSmalltalk.^[17]

The Thoth operating system provided either the basis or the inspiration for several later projects, some of which are listed below.

• The microNet distributedfile server system at the University of Waterloo ran on an operating system named WatSys that was similar to Thoth, and Port.^[24] WatSys debuted in 1981.^[25]
• TheNational Research Council of Canada was the development home of theHarmony operating system, a derivative of Thoth oriented towards real-time robot control.^[26]
• Cheriton took a position at theUniversity of British Columbia, where he was involved in developing Verex, and Distributed Verex, using many of the ideas he had earlier explored in Thoth.^[12][27]
• Cheriton later moved toStanford University in the US, where he developed theV-System, which continued to build on earlier work with Thoth.^{[15][28][29][30]}
• The Sylvan Multiprocessing system's architecture included a coprocessor that implemented Thoth's synchronous message passing primitives (and Ada's extended rendezvous) in hardware.^[16][31]
• Thoth and its message passing IPC were used to underpin a multi-process paint program that employed the anthropomorphic programming model.^[32][33]
• Thoth's message passing semantics were part of an experimental parallel-processing version of thecomputer algebra system (CAS)Maple.^[34]
• The distributed Process Execution And Communication Environment (PEACE) was developed for high-performance applications. The paper cites Thoth as a "major foundation" for the project.^[35]
• The Eindhoven Multi-Processor System (EMPS) executive put an emphasis on efficiency. Thoth provided the inspiration for the design of the EMPS kernel.^[36]
• An experimental human-computer interface environment named the Room system was built on Waterloo Port, which was derived from Thoth and which used its IPC techniques. The Room paper references earlier Thoth papers.^[37]
• The Flash web server, a research project with an emphasis on efficiency and portability, was said to resemble Thoth in its method of multi-process structuring and concept of process teams communicating via message passing.^[38]

• Gordon Bell andDan Dodge, developers of theQNX message passing realtime operating system, both worked with Thoth while they were students at Waterloo.^{[39][40][41][42]}
• AT&T'sSystem 75 Office Communication System was controlled by theOryx kernel and thePecos set of essential system processes, jointly referred to asOryx/Pecos. It used ideas from Thoth, DEMOS, and an internal AT&T project.^[43]
• The commercialWaterloo Port network operating system was derived from Thoth.^[44] The associated Zed language was upgraded to become the PORT language for Waterloo Port.^[45][46]
• Hayes Microcomputer Products acquired Waterloo Microsystems, and rebranded and upgraded the Waterloo Port product to createLANstep.^[47][48]
• TheAuspex storage company produced theFunctional Multiprocessing Kernel (FMK), which employed concepts identified as having been first developed in Thoth.^[49] Unlike the V-System and Waterloo Port, FMK had no memory management.
• Early versions ofNetwork Appliance, Inc.'s storage appliance operating system have been described as being very similar to Thoth.^[50] NetApp's OS was written byDavid Hitz, who had previously been at Auspex.
• In 1996 the CacheFlow web acceleration appliance company released theirCacheOS, which was based on Thoth.^[51] In 2001 CacheFlow was renamedBlue Coat Systems and, with the addition of a policy engine, CacheOS became theSecure Gateway Operating System (SGOS).

• Malcolm, Michael A.; Stafford, Gary J. (September 1977).The Thoth Assembler Writing Kit(PDF). University of Waterloo Computer Science Department (Technical report).
• Cheriton, D. R.; Murphy, W. (September 1979).Verex System Programmer's Manual (Technical report). University of British Columbia.
• Cheriton, David R. (1979).Designing an Operating System to be Verifiable (Technical report).
• Cheriton, D. R. (September 1980).The Verex Kernel (Technical report). University of British Columbia.
• Cheriton, D. R. (November 1981). "The Design of a Distributed Kernel".Proceedings of ACM National Conference.
• Wallis, Peter J. L. (1982).Portable programming. Macmillan.ISBN 0333310365.
• Cheriton, David R. (1982).The Thoth system: multi-process structuring and portability. North-Holland.ISBN 0-444-00701-6.
• Malcolm, Michael Alexander; Dyment, Doug (December 1983). "Experience designing the waterloo port user interface".Proceedings of the 1983 ACM SIGSMALL symposium on Personal and small computers - SIGSMALL '83. pp. 168–175.doi:10.1145/800219.806664.ISBN 0897911237.S2CID 14736242.

• Real-time operating systems
• Microkernel-based operating systems
• University of Waterloo
• Operating system families

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