General Electric Mainframe Computers

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GE-600 series

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The GE-600 series was a family of 36-bit mainframe computers originating in the 1960s, built by General Electric (GE). When GE left the mainframe business the line was sold to Honeywell, which built similar systems into the 1990s as the division moved to Groupe Bull and then NEC.

The system is perhaps best known as the platform on which the Dartmouth Time Sharing System (DTSS) spent most of its life, and the base machine for the Multics operating system as well. Multics was supported by virtual memory additions made to later versions of the series.



The 600 series used 36-bit words and 18-bit addresses. They had two 36-bit accumulators, eight 18-bit index registers, and one 8-bit exponent register. It supported floating point in both 36-bit single-precision and 2 x 36-bit double precision, the exponent being stored separately, allowing up to 71 bits of precision (one bit being used for the sign). It had an elaborate set of addressing modes, many of which used indirect words, some of which were auto-incrementing or auto-decrementing. It supported 6-bit and 9-bit bytes through addressing modes; these supported extracting specific bytes, and incrementing the byte pointer, but not random access to bytes.

It also included a number of channel controllers for handling I/O. The CPU could hand off short programs written in the channel controller's own machine language, which would then process the data, move it to or from the memory, and raise an interrupt when they completed. This allowed the main CPU to move on to other tasks while waiting for the slow I/O to complete, a primary feature of time sharing systems.

Operating systems[edit]

Originally the operating system for the 600-series computers was GECOS, developed by GE beginning in 1962. Between 1963 and 1964, the first version of the Dartmouth Time Sharing System (DTSS) was developed on the GE-235. DTSS was the first truly useful time sharing system and was very influential in the market. It is also the platform where the BASIC programming language was first developed. The Computer History Museum's Corporate Histories Collection describes GE's Mark I history this way[1]:

The precursor of General Electric Information Services began as a business unit within General Electric formed to sell excess computer time on the computers used to give customer demos. In 1965, Warner Sinback recommended that they begin to sell time-sharing services using the time-sharing system (Mark 1) developed at Dartmouth on a General Electric 265 computer. The service was an instant success and by 1968, GEIS had 40% of the $ 70 million time-sharing market. The service continued to grow, and over time migrated to the GE developed Mark II and Mark III operating systems running on large mainframe computers.

The GE Mark II operating system (later Mark III) was used by GE Information Services as the basis for its timesharing and networked computing business. Although Mark II / Mark III was originally based on the Dartmouth system, the systems quickly diverged. Mark II/III incorporated many features normally associated with on-line transaction-processing systems, such as journalization and granular file locking. In the early-to-mid-1970s, Mark III adopted a high-reliability cluster technology, in which up to eight processing systems (each with its own copy of the operating system) had access to multiple file systems.

The Multics operating system was begun in 1964 as an advanced new operating system for the 600 series, though it was not production-ready until 1969. GE was hardware supplier to the project and one of development partners (the others were Massachusetts Institute of Technology and Bell Labs). GE saw this project as an opportunity to clearly separate themselves from other vendors by offering this advanced OS which would run best only on their machines. Multics required a number of additional features in the CPU to be truly effective, and John Couleur was joined by Edward Glaser at MIT to make the required modifications. The result was the GE-645, which included support for virtual memory. Addressing was modified to use an 18-bit segment in addition to the 18-bit address, dramatically increasing the theoretical memory size and making virtual memory much easier to support.


The GE-600 line of computers was developed by a team led by John Couleur out of work they had done for the military MISTRAM project in 1959. MISTRAM was a radar tracking system that was used on a number of projects, including Project Apollo. The Air Force required a data-collection computer to be installed in a tracking station downrange from Cape Canaveral. The data would eventually be shared with the 36-bit IBM 7094 machine at the Cape, so the computer would likely have to be 36-bits as well. GE built a machine called the M236 for the task, and as a result of the 36-bit needs, it ended up acting much like the 7094.

GE originally had not intended to enter the commercial computer market with their own machine. However, by the early 1960s GE was the largest user of IBM mainframes,[citation needed] and producing their own machines seemed like an excellent way to lower the costs of their computing department. In one estimate, the cost of development would be paid for in a single year free of IBM rental fees. Many remained skeptical, but after a year of internal wrangling, the project to commercialize the M236 eventually got the go-ahead in February 1963.

The machine was originally offered as the main GE-635, and the slower but compatible GE-625 and GE-615. While most were single-processor systems, the 635 could be configured with four CPUs and up to four input/output controllers (IOC's) each with up to 16 Common Peripheral Interface Channels. The 635 was likely the first example of a general purpose SMP system, though the GECOS/GCOS software treated the processors as a master and up to three slaves.

In August 1964, IBM considered the GE 600 series to be "severe competition in the medium and large-scale scientific areas".[2] In May 1965 the first GE-625 computer was delivered to the GE Schenectady plant to replace five other computers of various sizes and makes.[3] A number of GE 635's were shipped during 1965 including two to Martin Marietta in November.[4]

The 600 line consisted of six models: the 605, 615, 625, 635, 645, and 655. GE offered a box to connect to the 635 called a 9SA that allowed the 635 to run 7094 programs.

The 615 was a 635 with Control Unit (CU) and Operations Unit (OU) overlap disabled, and a 36-bit-wide memory path. The 625 was a 635 with Control Unit and Operations Unit overlap disabled and 72-bit-wide memory path. The 635 had a 72-bit-wide memory path and CU/OU overlap enabled. The difference between these models was fewer than 10 wires on the backplane. Field service could convert a 615 to a 635 or 625 or vice versa in a couple of hours if necessary; other than those few wires, the 615, 625 and 635 were identical. The 605 was used in some realtime/military applications and was essentially a 615 without the floating point hardware. Programs coded for a 605 would run without any modification on any other 600 line processor. The 645 was a modified 635 processor that provided hardware support for the Multics operating system developed at MIT.

The 605/615/625/635 and 645 were essentially second generation computers[citation needed] with discrete transistor TTL logic and a handful of integrated circuits. Memory consisted of a two-microsecond ferrite core, which could be interleaved. GE bought core memory from Fabri-Tek, Ampex and Lockheed. The Lockheed memory tended to be the most reliable.[citation needed]

Continuing problems with the reliability of the magnetic tape systems used with the system cast a pall over the entire project. In 1966 GE froze many orders while others were cancelled outright. By 1967 these problems were cleared up, and the machines were re-launched along with an upgraded version of the GECOS operating system.

A follow-on project to create a next-generation 635 started in 1967. The new GE-655 replaced the individual transistors from the earlier models with integrated circuits, which doubled the performance of the machine while also greatly reducing assembly costs. However, the machine was still in development in 1969, and was announced but probably never delivered under that name.

By that time the Multics project had finally produced an operating system usable by end-users. Besides MIT, Bell Labs, and GE, GE-645 systems running Multics were installed at the US Air Force Rome Development Center, Honeywell Billerica, and Machines Bull in Paris. These last two systems were used as a "software factory" by a Honeywell/Bull project to design the Honeywell Level 64 computer.

GE sold its computer division to Honeywell in 1970, who renamed the GE-600 series as the Honeywell 6000 series. The 655 was officially released in 1973 as the Honeywell 6070 (with reduced performance versions, the 6030 and 6050). An optional Decimal/Business instruction set was added to improve COBOL performance. This was the Extended Instruction Set, aka EIS and the Decimal Unit or DU. The machines with EIS were the 'even' series, the 6040, 6060, 6080 and later the 6025. Several hundred of these processors were sold. Memory was initially 600 ns ferrite core made by Lockheed. Later versions used 750 ns MOS memory. The two could co-exist within a system, but not within a memory controller.

A version of the 6080 with the various Multics-related changes similar to the 645 was released as the 6180. A few dozen 6180-architecture CPUs were shipped. Later members of the 6000 series were released under various names, including Level 66, Level 68, DPS-8, DPS-88, DPS-90, DPS-9000 by Honeywell, Groupe Bull, and NEC.

See also[edit]



from GECOS to GCOS8

an history of Large Systems in GE, Honeywell, NEC and Bull

a view by Jean Bellec (FEB), from the other side of the Atlantic

Part I- General Electric

General Electric was in the early 60s the largest private user of IBM computers. GE had no intent of considering electronic computers as one of its strategic segments. However a decentralized management structure allowed the hyper frequencies lab to enter the computer field through a bid for the checks sorter shop at Bank of America. (ERMA project). That was the beginning of the Computer Department established at Phoenix AZ.

GE also embarked in the process control computer business through the GE-312 that evolve later into GE-225 and into GE-265 (Dartmouth Time-Sharing System). The first direct entry of GE in the general purpose computer business was a 24-bits machine code-named Mosaic that was introduced in 1963 as GE-400. However, the upper model planned for GE-400 was hardly competitive with the just announced IBM/360.

Origin of GE-600

A solution to the performance problem of the "Y" model of the GE-400 came from a project initiated outside the Computer Department , in the Military Department that had developed a computer for the US Air Force Cape Canaveral Missile Range, called M236 and installed at Eleuthera (Bahamas). That computer was a 36-bits computer due to the computation requirements of radar tracking and to the required exchange of data with IBM 7094 located at the Cape. The chief architect of the M-236 was John Couleur who will become later a technical leader of the GE Large Systems.

The debate in favor or against a M236-derived general purpose computer took more than one year and concluded finally with the victory of the M2360 project proponents in February 1963. The GE upper management was impressed by the perspective of saving the rental fees from IBM leased equipment used internally by GE (the cost of development of the new project was estimated to be offset by only one year of rentals). The other GE departments were not very impressed and were reluctant to jettison their IBM machines.


According to the initial plan, the central processor was to be designed at Syracuse, NY and the Input-Output Controller in Phoenix, with peripheral subsystems common to the GE-400 line. The product line took the name of GE-600 initially with two system versions with different clock values, the GE-625 and the GE-635. The software would have been developed in Phoenix with people brought from various user departments. Eventually, the processor's team migrate from Syracuse to Phoenix, while the technology team remained for a while in Syracuse.

The main innovation of GE-600 was the creation of a SMP Symmetric Multi-Processing platform, probably the first actually built in the world. While, at that time, much talk was about the reliability of a redundant system, the main advantage was different: SMP was limiting the development cost to a single design for building a line covering a range of power that would had needed probably three designs (as IBM did at that time).

In 1964, GE decided to take over Olivetti computer assets and the majority of Compagnie des Machines Bull of France. The expected value of those acquisitions was to establish an international European base for the general purpose computers. Both the GE-400 and the GE-600 were to be sold by the two European subsidiaries of General Electric.

The first GE-600 introduced in Europe was a GE-635 sold to ASEA in Sweden before the Bull-GE merger. ASEA (now part of ABB) was a General Electric licensee and used the GE-600 for scientific applications.

After jettisoning its RCA licenses, Bull was selling many GE-400 systems and started to market the GE-600 over its original market. It got a contract for the billing of Electricité de France , the largest power utility in the world, that required COBOL, while the compiler was still in its infancy in Phoenix. It required far more reliability from magnetic tapes than GE was then providing. GECOS II was an operating system that was optimizing batch processing (without an attached processor, as were at that time organized many IBM shops) and remote-batch (using Univac 1004 or GE-115 small computers as terminals). It supported multiprogramming but not very efficiently.

In 1964-1966, But obtained contracts for around a dozen of GE-600. But eventually, the EDF contract collapsed and Bull-GE froze its ordering of GE-600, waiting the solution of the technical problems that finally were sorted out in 1968.

During that period, Bull-GE made studies, in conjunction with Phoenix, of a small version de GE-600, code-named Q2, that proposed a micro-programmed version of the 600. The project was cancelled when GE was no more sure of pursuing the GE-600 line.


The initial GE-600 systems were using GECOS-II operating system, a multiprogramming batch oriented system, based upon large (specifically IBM 7090) users requirements of that time. Thanks to the multiprogramming facilities of the OS, there was requirements for supplemental I/O converters (à la 1401) and remote batch was supported with initially Univac 1004 as terminals.

Programming Languages were:

  • GMAP macro assembler


  • COBOL 61

  • that was announced and "delivered" far before being qualified. in 1965


  • for an USAF contract

Files on tape and discs supported sequential and random organizations (GEFRC) and IDS was being announced.

The insufficient quality of GECOS-II associated to the poor reliability of the magnetic tapes lead, in October 1966, to as suspension of the promotion of GE-600 in the United States and of is sales by General Electric, some orders were cancelled, other delayed and the future of GE-600 was somber.


The operating system kernel was redesigned, adding also a time-sharing system (TSS) extending the functions of the Dartmouth Time Sharing System on the GE-265. It became GECOS III and was well accepted by existing customers. Introduced in 1968, while MULTICS was still in its infancy, no commonality was envisioned between GECOSIII and MULTICS.

GECOS III was advertised as a multidimensional system, adding to batch and remote-batch, the time-sharing and direct-access "dimensions". The architecture of GECOS III will not be significantly altered in the future versions of GCOS.

The new operating system, announced in 1967, gave the opportunity to re-launch the marketing of the 635 line and in Europe several new large orders were secured (Credito Italiano, l'Union) specially for large business applications. Bull lost the scientific market to Control Data, Univac and IBM but succeeded to make an honorable stand in the non-scientific market.

In the US, GE succeeded to secure a large order from US Air Force for its Worldwide control & command system (WWMCCS). Some modifications to improve the security of GECOS III were developed as specials for that order, but the existence of this multi-year contract was securing the durability of the product line. A few WWMCCS systems were installed in Germany.


The technology of the GE-635 was based on discrete transistors (Sylvania SUHL). Printed circuits were not fully used and the manufacturing cost of a system was high. A single processor system represented three large cabinets not including peripherals.

A first improvement was brought in 1967, when a new model with an integrated circuits technology was designed by the Syracuse team of GE. Its performances were better than those of the 635 and the manufacturing cost lower. It was introduced as the GE-655 at a price significantly higher than that of the 635.


GECOS-IV was a project developed in Central research Laboratory in Schenectady in 1967 under the direction of Robin Kerr. Their goal was to integrate GECOS, the work at Dartmouth and the their DESKSIDE project. GECOS-IV required a modified CPU to provide a "virtual machine" capability. It also challenged a strength of GECOS-III, its time-sharing capability.

Mark-III and General Electric Information System

In 1964, GE had helped the Dartmouth College NH to develop an interactive system for teaching programming. The hardware was a GE-200 front-ended by a communication processor developed initially for store and forward communication messages the GE Datanet-30. The terminals were AT&T Teletype 33 ASCII typewriters connected through 300 bauds Bell modems.

The Dartmouth College, perhaps inspired from MIT CTSS, had developed a special purpose operating-system including an interpretive processor of the BASIC (Beginner's All Symbolic Instruction Code) language also created for this system, christened GE-265.

General Electric started to market the BASIC service, through a special division that took over the maintenance of the Dartmouth College software. As the hardware perspective of the GE-200 was limited, the Dartmouth College accepted the GE offer of porting the DTSS (Dartmouth Time-Sharing System) to the GE-600. GE started to replace its GE-265 by GE-635 as Mark-III systems.

The hardware of Mark-III system was originally completely standard, but the software was developed and maintained independently from Phoenix. General Electric Computer Division and its affiliates (e.g., Bull General-Electric) were not entitled to license their customers with Mark-III software.

Mark-III systems main center was concentrated in Cleveland OH, but expanded with a center in Amsterdam, the Netherlands. The customers of the timesharing service were connected transparently to the computer centers.

With Mark-III, the applications were expanded to email and batch applications. Eventually, GE added to the base systems several IBM 370 computers to provide batch services without recompiling applications to the peculiarities of GE-600 code (differences in scientific operations precision in particular.

GE ISD was later instrumental in the evolution of Honeywell Large Systems by pushing Phoenix to use IBM and IBM compatible peripheral subsystems on the DPS-8 product line. GEISD had developed since the early 70s their own versions of peripheral subsystems shared between Honeywell and IBM computers and pressured Honeywell to introduce a standard facility.

After acquisition of the GE computer business by Honeywell in 1970, General Electric kept the timesharing business in an Information Services Division that is still alive. The ISD European Operation was momentarily kept inside Honeywell-Bull, but was retroceded to GE circa 1975.


Toshiba Corporation was a licensee of General Electric in Japan and also using the computer licenses of the GE-600. The Japanese , at the end of the 1960s, started to design their low-end version of the GE-600. They used obviously integrated circuits and designed a micro-programmed execution unit. Under the provisions of cross-licensing, Toshiba's design was later brought back in Phoenix under the ELS (entry level system) code name.

In 1973, Datamation reported, from information apparently collected from Richard Bloch that In 1969, John Haanstra, somewhat skeptical about the results of the Shangri-La task force attempted to establish as a parallel effort or as a back-up effort a project, to be done in cooperation with Toshiba that would have closed the gap between the GE-400 and the GE-600 product lines. It would have been a dual-personality machine operating in GE-400 as a 3xGE-435. The death of John Haanstra in August 1969 would have suspended the project.

[I have been unable to find a person who in Phoenix or in Bull had the knowledge of the Pi project, so I would be interesting to know more about it. For the time being, I am unable to confirm or to infirm its existence. JB]

GE APL advanced product line

Around the end of 1967, however, IBM S/360 was starting to submerge its competitors and GE had to recognized that its set of product lines covered few segments with a competitive edge.

John Haanstra (who headed several IBM technical departments) was hired by GE to design a plan to replaces current product lines by a new Advanced Product Line (APL). Forces from Paris, Milano and Phoenix started to work together on that project. The revival of the GE-600 did not materialize before 1969 and the APL did not target the still embryonic park.

GE choose a new (CML) technology for APL, what was somewhat premature .

John Haanstra left APL to head the Phoenix computer department, were he brought impulses from the APL project, such as 9-bits PSI channels, microprogrammed peripheral subsystems that improved the GECOS offering for many years to come.

After a new attempt by GE to redefine a new product line (in a 4 months meeting named Shangri-La in summer of 1969), the GE management finally decided in April 1970 to sell its Computer Department. Honeywell was the buyer of all the assets (including Phoenix as well as the European subsidiaries)

[part II Honeywell [part III NEC and Bull]


Revision : 20 février 2003.