Gamma 3


The first electronic computer produced by Compagnie des Machines Bull was developed in the 1950s as a complement to the Series 150 punched card equipment.

What was initially a simple calculator evolved progressively into a general purpose computer using the Series 150 punched card equipment as peripherals.

The Compagnie des Machines Bull electronic calculators, and subsequently its computers, were named Gamma xx sometimes abbreviated as Γxx.

Gamma 2

A preliminary version of electronic calculators was introduced in October 1951 as Gamma 2 connected to E-120 tabulator.

Gamma 3

The design of that computer started in the recently electronic lab of avenue Gambetta in Paris. The key designers were Bruno Leclerc, Pierre Chenus and Henri Feissel. It was announced in 1952. The first shipment was in March 1953 for Crédit Lyonnais at Saint-Etienne (France).

The Gamma 3 has functions quite similar to IBM 604.


The Gamma 3 cannot be considered as a Von Neumann machine. The commands were stored in a wired down  "connection panel". Gamma 3's connection panel might store a maximum of 64 commands called "program steps".

The "data memory" of the Gamma 3 was limited to registers (including accumulator) each containing a word of 12 decimal digits.

The clock of the Gamma 3 calculator is synchronized with the frequency of the motor of the connected electromechanical equipment. Generally, that machine was a tabulator, sometimes a PRD (card reader punch). Series 150 base frequency was 2.5 Hz. The corresponding was 400ms. With tabulators, only 40ms of inter-cycle time were available for computations, with the PRD, the inter-cards time gave 107ms.

Data handled by the Gamma 3 were BCD 4-bits numeric digits.



this photograph of a Gamma 3 preserved at Aconit, presented at the exhibition of 6th Colloque de l'histoire de l'inforamatique et des Réseaux in 2002 shows at the left an additional programming panel, in the middle the electronic racks and their tubes, on  the right the set of electromechanical relays for interconnection with the tabulator and on the bottom the cables (nicknamed "boas") interconnecting cabinets. 

The main memory of the Gamma 3 was built from 15 shift registers (containing 48 bits) on a magnetostrictive technology. The basic clock time (time to shift one bit in the register) is 172 microseconds (µs).

Registers M1 and M2 are also accumulators for fixed point decimal operations. The arithmetic operator (adder-subtractor) is bit-serial.

The processor clock is 281 KHz.

Loading a 16-bits instruction took 520 µs . The duration of instructions execution varied from 0.6 ms to 10 ms (mean time 2 ms).

The processor used around 400 vacuum tubes and germanium diodes that help to improve the reliability, compared to a valve only machine .

The connection with the electromechanical elements was made 48-bits parallel using big "boa" cables.


The Gamma 3 basic "standard" model had a memory limited to 4 words and 32 instructions steps. The design point model includes an extension called AEP "Armoire d'Extension Programme" (Program Extension Cabinet).

Gamma 3A

Gamma 3M

A first extension was to allow the overlap of computations and electro-mechanical operations.

Gamma 3M included additionally had a "sign" register. The memory could be extended up to 31 words by adding 1 to 3 additional cabinets (AMS "armoires de mémoires supplémentaires")

Another optional feature of Gamma 3M was the Cards Programming Feature (PPC "Programme par cartes"). That feature allowed the fetching of instructions from punched cards as well as connection panel.

Gamma 3B

This model replaced the earlier models. The AEP feature was extended to 128 instructions (from connection panel) when the data memory is limited to 24 words.

gamma3_cab.jpg (20620 octets)

Gamma AET

This model was announced in 1955 and is also known as Gamma 3BT.

One of the problem encountered in previous models was the constraint of manually swapping connection panels in the different phases of operation. Adding a magnetic drum meant that the equivalent of many panels could be selected under program control.

As well, it became possible to store data on the drum.

Gamma AET (AET for "Armoire d'extension Tambour" ) that included the capacity of storing data and programs was introduced in 1956.

Gamma AET was including 4 sets of 16 words.

The drum capacity was 8192 48-bits words and had an access time of 12 ms.

The "wired" connection panels remained used for standard subroutines (noticeably the floating point operations), because their faster access time.

Gamma AET was a major point of evolution towards the general purpose computer, however, it was still synchronized and slave of the electromechanical equipments.


An extension was introduced to Gamma AET, ACIE "Armoire Complémentaire et d'extracteurs", allowed the Gamma AET to address the full contents of cards and not only the colons selected for tabulator own usage.


Gamma ET

This model was also called "Ordonnateur" , an answer to the use of IBM France to use the, now accepted, term "ordinateur" for naming an electronic computer in French. This model was also known as Gamma 3B2T.

It was announced in 1956.

The Gamma ET's processor was now the center of the system and uses the card equipment. The peripherals devices (maximum of two) were tabulators, PRD or ULP -two kinds of reader/punches. The input-output operations became asynchronous.

The capacity of the magnetic drum was extended to 16K (16384) words. The main memory was 128 words, 64 of them can contains instructions.

An entry model of Gamma ET included 64 words of main memory.

Gamma ET took an important position on the French scientific market in the second part of the 1950s. A scientific center, CNCE Centre National de Calcul Electronique, had been established by Bull from 1951 and was used by French and European labs that had not computers on their own. CNCE became very important with Gamma ET.

The total park of Gamma 3 can be estimated at 1200 in Europe, the large majority of them being leased , not sold, to customers. The competition was essentially IBM 604 for Gamma 3, IBM 650 for Gamma ET.


The evolution from Gamma 3 to Gamma ET  did not imply changes in the technology and Gamma ET could be manufactured with parts of recycled Gamma 3. During the 1950s, Bull could entertain its customers with a single line of hardware, centered on its electro-mechanical equipment.

The success of Gamma ET somewhat eroded the IBM domination in Europe. But, IBM,  with the 1401 computer, caused its own park to be replaced my new equipment. Bull attempted to follow suit with a brand new set of card equipments, the Series 300. Renewing the leased park represented the write-off of a marge quantity of equipments that were, added to the cost of Gamma 60, a fast deterioration of Bull's financial position in the early 1960s.

Gamma 3 contributors


Revision : 06 décembre 2002.