Bull Gamma 60
In 1960, Compagnie des Machines Bull, a flagship of French industry, unveiled an exceptional creation: the Gamma 60. This machine, designed to handle both commercial and scientific tasks, made its mark through bold technical innovations.
The Gamma 60 stood out through its radical approach to information processing. Its distinctive feature was its ability to manage functions or problems simultaneously without specific programming of this parallelism. A technical achievement that enabled maximum utilization of hardware resources.
The internal organization followed a forward-thinking modular logic. Its core operated around a main unit equipped with magnetic core memory, coupled with a superior control unit. The latter comprised two strategic elements: a program distributor and a data distributor. Various specialized units revolved around these: arithmetic, logic, comparison, translation, magnetic drum storage, not to mention input-output devices such as card and tape readers, punches, and printers.
The main memory utilized saturated magnetic core technology, with 32,768 “catenæ”—blocks of 24 bits representing approximately 786,432 bits. This capacity allowed storage of 196,608 decimal digits or 131,072 alphabetic characters, with each catena accessible in just 11 microseconds. The Latin term “catena” meaning “chain” was deliberately chosen by the engineers to distance themselves from Anglo-Saxon computing vocabulary. This evidently did not catch on.
The Gamma 60’s coding system demonstrated remarkable adaptability. Numerical data used a 4-bit decimal code, while alphanumeric data employed 6 bits. Instructions appeared in pure binary. This variety of formats aimed to save space, encode efficiently, simplify conversion between media, and maximize transfer rates.
The arithmetic unit performed operations on both fixed-point and floating-point numbers. The numerical representation utilized two catenæ, structured with a sign bit, 40 bits to encode 10 decimal digits, and 7 bits dedicated to the decimal exponent, covering a range from 0 to 79. Depending on their complexity, instructions required 2 to 4 catenæ. For example, a three-address floating-point addition took 150 microseconds, compared to 88 microseconds for a single-address version.
The system’s peripherals displayed solid performance. The magnetic tape units used half-inch media with 8 information channels. With a density of 200 bits per inch and a running speed of 50 inches per second, they achieved throughputs of 20,000 decimal digits or 13,333 alphabetic characters per second. The readers processed 300 punched cards per minute, while flywheel printers produced 300 lines per minute, each capable of containing 120 characters from a palette of 60.
The Gamma 60’s true breakthrough lay in its control organization. Each functional element had its own program and its own control unit. Once configured, these modules operated in complete autonomy. Only the main memory and transfer buses were shared among the different units. The program distributor orchestrated the distribution of instructions and established the necessary locks to prevent conflicts between concurrent programs. In parallel, the data distributor managed access priorities to the transfer buses.
This sophisticated architecture enabled the side-by-side execution of highly heterogeneous tasks: payroll calculation, matrix inversion, multiple conversions from tape to printer, from cards to magnetic tape, or from punched ribbons to magnetic tape. And this with virtually no performance loss: the time lost in this simultaneous execution almost never exceeded a few percent compared to sequential processing.
Emerging from the French computer industry of the 20th century, the Gamma 60 was marketed starting in 1960, but its trajectory was unfortunately cut short by Bull’s financial difficulties, which led to the company’s acquisition by General Electric in 1964. This acquisition ended the independent development of the machine, but its concepts regarding parallel processing and modularity were innovative.