The picture shows Gamma 3 with the front panels removed. On the right hand side we see the vacuum tube stands (Rörstativ) opened. Gamma 3 had about 400 vacuum tubes (also called radio tubes or electronic tubes — Elektronrör in Swedish). Modern computers often have billions of transistor functions (where every transistor has the same function as the radio tubes above (sometimes the expression radio valves is used). One of the main problems with electronic tubes was their limited life time, about 500 hours. This leads to insurmountable problems if you have tens of thousands of tubes (Gamma had only 400 so for this particular machine the limited life span of vacuum tubes was not a problem). One or several tubes will always be non-funtional. And as soon as you have replaced those faulty tubes another tube has already broken down. The life span for transistors and chips (integrated circuits) are tens of years and in practice it is extremely rare that a transistor or a chip has to be replaced. Thus, under normal circumstances, transistors and chips have the same life span as the apparatus they are parts of. Vacuum tubes are therefore easily accessable (as can be seen in the picture above) och are mounted in special sockets. When replacing a tube the old tube is pulled out and the new tube is pressed down into the socket. The whole process will only take a few seconds. The sockets, unfortunately, cost a lot of money and are bulky. Transistors and chips are soldered and can be difficult to replace. Which, as has been explained above, is not a problem, as they almost never need to be replaced.

Vacuum tubes demand a lot of energy and although there were rather few vacuum tubes in Gamma 3, a large power unit was needed. About half the volume of the Gamma 3 (the left half of the cabinet) was used for the Gamma 3 power supply (Nätaggregat).

Dear reader, contemplate for a while that in your smartphone there are billions of transistors (transistor functions), which are functionally equivalent to vacuum tubes (1 transistor equals 1 vacuum tube) in the technology contemporary to Gamma 3. The picture above gives the reader an ideia of the size of a vacuum tube (length about 5 cm) which should create in the reader the appropriate feeling of awe and wonder over the almost miraculous development of electronics during the period from 1940s up to today. Had anyone 1953 suggested that within 60 years a volume of a few cubic centimeters will accomodate billions of vacuum tubes (or its equvivalent) this person would have been regarded as a fool or an utterly idiot.

Gamma 3 was not an autonomous computer but an extension to the tabulator Series 150, described in the main article (see figure 3). Initially it was programmed in the same way as the tabulator (by wires on a plugwires panel — see figure 4 in the main article). Gamma 3 replaced the slow tabulator calculations by relays with thousands of times faster electronic calculations by vacuum tubes. Eventually Gamma 3 was improved to be programmed via punched cards which made it possible to use modern programming languages. This was a giant step forward. The former director of the BULL company, Pierre Letort, described in the magazine Arts et Manufactures, No. 22, dated June 1953, the operation of the GAMMA 3:

In its current configuration, the computer [Gamma 3] acts as an extension unit for the punched card machine it is connected to [Series 150]. The cards are read in the reader station [on the punch card machine] which transmits data to the computer.[Gamma 3]
The computer in turn performs all necessary calculations and transmits the results back to the punched card machine [Series 150] which will print [on paper] or punch these values [on punch cards]. Regardless of the task, the computer [Gamma 3] is so fast that there is no visible delay caused by the calculations

Almost all computers today have von Neumann architecture. John von Neumann (1903-1957), sometimes called Einstein's equal, was a brilliant mathematician and theoretical physicist of Hungarian ancestry. He made decisive contributions to many fields of mathematics and physics, e.g. quantum physics, economy (game theory), topology, numerical analysis and last but not least computer science. He, more than anyone else, laid the foundation for the modern computer by specifying what different functions a programmable computer must have. Thence the expression "von Neumann architecture". The first generations of computers used in business, economy and similar areas (like Bull Series 150 and Gamma 3 and IBM's corresponding machines) were not "von Neumann computers" in the true sense. But they worked in a similar way and were programmable (within certain limits). And they are undoubtedly an important part of the development of the modern computer.

Here you can read more about Bull's machines and their history:
Bull's different machines (history)
A short summary of Bull Gamma 3

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