BESK (Binär Elektronisk SekvensKalkylator, Swedish for "Binary Electronic Sequence Calculator") was Sweden's first electronic computer, using vacuum tubes instead of relays. It was developed by Matematikmaskinnämnden (Swedish Board for Computing Machinery) and during a short time it was the fastest computer in the world. The computer was completed in 1953 and in use until 1966. The technology behind BESK was later continued with the transistorized FACIT EDB and FACIT EDB-3 machines, both software compatible with BESK. Non-compatible machines highly inspired by BESK were SMIL made for the University of Lund, and DASK made in Denmark.
BESK was developed by the Swedish Board for Computing Machinery (Matematikmaskinnämnden) a few years after the mechanical relay computer BARK (Binär Aritmetisk Relä-Kalkylator, Swedish for "Binary Arithmetic Relay Calculator"). The team was initially led by Conny Palm, who died in December 1951, after which Stig Comét took over. The hardware was developed by Erik Stemme. Gösta Neovius and Olle Karlqvist were responsible for architecture and instruction set. It was closely modeled on the IAS machine for which the design team had retrieved drawings during a scholarship to Institute for Advanced Study (IAS) and Massachusetts Institute of Technology, U.S.
One spin off effect from the BESK works is still the design of the magnetic Drum memory. At this time Olle Karlqvist discover a magnetic phenomenon, which has been called Karlqvist gap.
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BESK was a 40-bit machine; it could perform an addition in 56 μs and a multiplication took 350 μs. The electrostatic memory could store 512 words. The instruction length was 20 bits, so each word could store two instructions. BESK contained 2400 "radio tubes" (vacuum tubes) and 400 germanium diodes (so it was partly solid state). The power consumption was 15 kVA.
Initially an average runtime of 5 minutes was achieved before hardware problems appeared. In 1954 the system became more stable. Breakpoints were introduced to allow software restart after hardware failures.
Originally BESK had a British Williams tube 40 bit memory with 40 cathode tubes, and 8 spare tubes. The memory was from the beginning found to be insufficient and Carl-Ivar Bergman was given just a few weeks to build and install a ferrite core memory in 1956. To get finished before the deadline they hired housewives with knitting experience to make the memory. One of the new memory bits did not work at first, but it was easily cut out and replaced.
The first calculations were done on April 1, 1954 and BESK handled weather data for Carl-Gustaf Rossby and the SMHI meteorological agency, statistics for the telecommunications service provider Televerket, wing profiles for the attack aircraft Saab Lansen, and road profiles for the road authority Vägverket. During the nights Swedish National Defence Radio Establishment (FRA) used BESK for decryption of radio messages. BESK was also used for calculations for the Swedish nuclear energy industry, for example Monte Carlo simulations of neutron spectrum, and for the Swedish nuclear weapon program, but most of those calculations were done by SMIL. In 1957 Hans Riesel used BESK to discover a Mersenne prime with 969 digits - the largest prime known at the time.
SAAB rented computer time on the BESK to (probably, much was secret) make calculations of the strength of the Saab Lansen attack aircraft. In the fall of 1955 SAAB thought the capacity was insufficient and started working on SAABs räkneautomat SARA, "SAAB's calculating machine", which was going to be twice as fast as BESK. Some former SARA employees went to Facit and worked with the Facit EDB.
"Besk" is Swedish for the taste "bitter". It is also the name of a traditional bitter made from distilled alcohol seasoned with the herb Artemisia absinthium L. local to the province of Skåne, in which Lund is located. Reportedly this was an intentional and unnoticed pun after officials denied usage of the name CONIAC (Conny [Palm] Integrator And Calculator, compare Cognac and ENIAC) for the predecessor BARK.