Bull Small Systems

Line 50, GE-55, Level 61...

Summary of a family of products designed by Bull and conveyed through the different avatars of Bull-General Electric, and Honeywell-Bull during 1960s and 1970s.

The line of products was targeted towards new customers, unable to cope with the cost of a card equipment shop but that wanted a better business automation than classic accounting machines were able to provide.

The main architect of that line was Claude Bouvier and the first machine was commonly surnamed the " Machine Bouvier ". More officially, the line was known as "Petite Machine". The design started in 1960-1961 just after the termination of the realization of Gamma 60.

Among the basic ideas around the Line 50 architecture, was that small systems customers could not afford the cost of learning the software (such as the one needed for Gamma 60 or even Gamma 30). That lead to the design of a "high level machine language" and of processor hardware to support it.
The architecture did not challenge the acceptance of fixed length punched cards   paradigm for representing the business data, but assumed a direct entry of data by the operator and mot requiring auxiliary punched card equipment.


Part of the main memory was used for dedicated peripheral buffering.

The memory was originally visible as 100 registers, 10 of them being area pointers ("adresse de zone"). Variable length data fields are stored in memory delimited by flags.  Addressing was decimal to simplify programming. Later the architecture evolve towards a more standard visibility.

Alphanumeric data are stored as 6-bits characters

Instructions were performing the following functions

  • Move  between peripheral buffers and registers

  • Arithmetic computation between registers (operating on 2 operands and with automatic normalization)

  • Peripheral operations (asynchronous or synchronous)

The central processor included a control store used to store the microprograms interpreting the architecture.


The system was based on a  ROM control store, made from magnetic rods (developed by Yves Brette and also used in the Gamma M-40).

The R/W memories were using magnetic cores and were addressed through an "incrementer" memory controller (a Claude Bouvier and Yves Brette  invention)

Models History

The first design of "Petite Machine" , also called Gamma 5, had the following characteristics

  • Data storage was limited in the first version to 160 or 320 characters .
  • The program was stored either on a loop of punched paper tape (entry level) or on a magnetic drum. It was buffered in a separate program cache storage.
  • The minimum I/O devices were a "Flexowriter" typewriter and a card reader/punch.

A few prototypes were built and used internally (e.g. by customer support inventory management) , but had  a cold reception by the Bull sales network, that estimated "not to be in the accounting business". The competition was IBM 632, a machine supported by IBM Office division.


A redesign lead to the introduction of GE-55, a derivative of the "Petite Machine", but a higher model that may be offered as a substitute to the electromechanical card equipments in the Series 150. Batch processing was a goal and the interactive mode, only an option.

GE-55 control store used the same ferrite rods technology. Data and programs were stored in an extended size memory 2,500 or 5,000 characters. The character size was extended to 8-bits (as in GE-100). The typewriter was replaced by  separate keyboards (alphanumeric and numeric) and  printer. The card reader was extended to reading optical marks and the card punch was separate.
Optional external storage was provided by a 89,600 bytes magnetic drum and/or cheap magnetic tapes (MTU 050, using a 35mm format tape). Printer was either serial (MB 50, then MB-40) or medium-speed line printer (I41)

The GE-55 programming system was intended to be based on a library of modular applications to be parameterized and generated (on Gamma 60, then on GE-400). That system was known as PROSPER ("Programme Standard PERsonnalisable")
There was a small operating system BOS provided in two versions Card  (BOS-C) an drum (BOS-MD) that was partially implemented in ROM.

The development of a symbolic assembler (GESAL) and of an extended operating system was made on GE-55 but was exploited on the next models.

The GE-55 was introduced by Bull-General Electric and was the first mass production of Bull.


It was succeeded by GE-58, introduced early in 1970, to benefit from technology improvements and from software new developments.

GE-58 technology was updated. The logic used TL integrated circuits. ROM control store abandoned magnetic rods to resistors. Main memory was extended to 10,000 characters (still magnetic cores). Peripherals of the card version of GE-58 were unchanged from GE-55.

GESAL was extended to allow symbolic names for program labels and data. The operating system become EOS-C that provided a multi-tasking support to GESAL programs. A Mini-COBOL, actually a COBOL -look alike language- was developed. Mini-COBOL programs were partially interpreted.

The control store technology changed again in the disc GE-58 , using successively ROM and PROM. The main memory introduced DRAM in 1973.
Two types of discs were used DSU-110 and DSU-160 (2.5 MB or 5 MB capacity).
An optional SLC single line controller allowed the GE-58 to be used for remote batch.

The operating system was DOS (Disc Operating System) and the software evolve towards the standards of the industry with a COBOL and a FORTRAN compilers.

In 1973, it was decided to supplement the single-user GE-58 by providing a multi-user (4) version of that system. It was introduced as part of the Honeywell Series 60 as the Level 61 system.

The 61-58 was identical to the disc GE-58, but received a MLC-050 multi-line controller supporting 4 asynchronous lines.

The DOS operating system was complemented with a Multi-users supervisor, providing a swapping storage for each user program and a message processing program. The normal mode of operation was to update files in batch mode.

In 1974, the responsible managers of Honeywell-Bull Small Systems Department observed that the main drawback of their system architecture was the limited size of main memory and went shopping for a front-end processor. Honeywell provided FEPs were too expensive and it was decided to import the Datapoint 2200 as the Level 61 front-end.

The FEP of 61-60 included a Datapoint processing unit, 16 KB of main memory, up to 16 serial interfaces, tape cassettes (2) and an alphanumeric CRT display (12 x 80 char). It also had an optional synchronous communication line to work in "distributed network".

Apart from the communication lines buffering and assembly the FEP software had a message-passing interface with the Level 61 operating system. The job scheduling was also moved to the FEP.

The addressing limitations of the processing unit was not sufficiently removed by the introduction of the FEP, specially with up 16 different users. So, a new model of the 61/60, the 61/60-2 was introduced in 1977

The 61/60-2 main processor was redesigned in a fully upward compatible version. The main differences was the extension of the main memory in 4 or 8 partitions of 16 KB. The decimal mode of addressing was kept (partitions limited to 10KB) in addition to a new binary mode (for 16KB partitions). New instructions were added moving some standard subroutines to PROM.

The operating system was altered by the new memory scheme. Partitions were allocated on a dedicated manner (one to FEP triggered programs, one to user batch applications, other to system tasks).

Very few efforts were made on Level 61 towards Level 62 compatibility. A GE-58 emulator was provided by Honeywell Italia on Level 62/DPS-4 for trying to upgrade users that remain in batch mode. In 1978, Level 6 emerged as   another contender for the low end business market. CII-Honeywell Bull attempted to focus its effort on level 6 (even at the price of a duplication with Boston's ones). The Small System Department started the development of conversion programs from 61 to Mini 6 (a French name for Level-6) under the code name of 61FS. One of the few fallbacks of this effort was the development of the Level 61 database multi-index organization (MLDS) on GCOS 6 Mod 400 as it had also been  developed for GCOS 62/4 and as it will be eventually implemented on GCOS7.

In parallel, the Small System Department pursue its efforts to improve its products and succeeded to introduce the 61-DPS in 1979. 61-DPS was introduced simultaneously with other models of the Honeywell Series 60, in reaction to IBM lowering of prices with 43x0 models. SSD benefited from this grouped announcements to circumvent the objections of other department to the non-discontinuation of that product line.

The Datapoint 1800 , more powerful than original 2200,   was the new Distributed Resources Processor (DRP) and the back-end processor became the Centralized Resource Processor (CRP)?

The distributions of functions between DRP and CRP was somewhat altered and the programmer interface, initially based on a message  line interface was changed into  a form level interface (Autoform).

The 61-DPS was the last system of the Bull Small System Department. In 1980, the SSD hardware team started the design of an integrated microprocessor able to emulate the CRP and the DRP. This project was called 1500 or Epsilon. But the project was terminated after the implementation of the first prototype, essentially on a business basis. New internal  competitors emerged: in the late 1970s, CII-Honeywell-Bull acquired R2E that designed Bull Micral Intel-based systems using the multi-user Prologue operating system;  UNIX systems started to be introduced by Honeywell and Groupe Bull in the 1980s.

 Revision : 02 mars 2007 .

1998 Jean Bellec from documents prepared by Ren KOEBEL 1994 for FEB.