# BESM-2 Computer

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- BESM-2 – a general-purpose electronic computing machine.
- The chief designer was academician of AS USSR S.A. Lebedev; the development team: K.S. Nesloukhovsky, A.N. Zimarev, V.A. Mel'nikov, A.A. Pavlikov, A.V. Avayev, and others.
- Developing organizations: the Institute of Precise Mechanics and Computing Equipment, the Volodarsky Plant, Ulyanovsk.
- Producer: Volodarsky Plant, Ulyanovsk.
- Development was completed by 1957.
- Manufacturing started in 1958.
- Production stopped in 1962.
- Number of issued computers: several dozen.
- Applications: in computer centers and research organizations – for numerical solutions of a wide range of mathematical tasks.
- System architecture: 39-bit binary floating point notation (32 bits for mantissa; 1 bit for number sign, 5 bits for exponent, 1 bit for the exponent sign). Numeric range was 10
^{-9}–10^{9}. Calculation precision was approximately 9 decimal signs (it was also possible to perform double precision calculations).The instruction set comprised instructions using 3 addresses for operands. The instructions were 39-bit long (6 bits for operation code plus 3 pointers with 11 address lines each). The instruction set of the computer included arithmetic, logical, control and code transfer operations. The computer could perform operations with normalized and non-normalized numbers.

BESM-2 had a single arithmetic unit, which was universal. The system of code exchange between the arithmetic unit and the main memory device used a parallel scheme. The control for the standard instructions was centralized and those instructions whose execution time did not fit to the standard cycle of the central control were managed locally.

The BESM-2 RAM was based on ferromagnetic cores and held up to 2047 of 39-bit numbers. The RAM sampling rate for one number was 10 µs.

Magnetic drums and replaceable magnetic tapes served as external storage devices. The capacity of each magnetic drum was 5120 numbers or more. Read or write rate was 880 numbers per second. The impulse frequency of a magnetic drum was about 35 kHz. The maximum wait time before reading the first number was 80 ms, the average read wait time was 40 ms. There were four magnetic tapes that could be recorded in the group-by-group mode. Each group could comprise up to 2047 numbers. The capacity of each tape was not less than 40 000 codes. The speed of read or write operations reached 400 numbers per second. The impulse frequency of a magnetic tape was about 16 kHz. The magnetic tapes could wind either forward or backward, but data transfer occurred only during the forward move.

Programs and data were input from a punched tape with the speed of 20 codes per second. The results of calculations were printed directly to paper with the speed of 20 numbers per second. System faults were localized with the help of series of tests and switching the computer into the manual operation mode.

- System electronics: two-tube cells, into which various circuits were mounted (triggers, valves, amplifiers, etc). The BESM-2 computer contained about 4 thousand electronic tubes.
- System design: BESM-2 was assembled in three basic racks. There were also racks for the magnetic RAM (MRAM) and for the control panel that was used to start and stop the computer and to monitor its operation.
- System software: There was no system software on this computer.
- Characteristics:
- average performance – 8000–10,000 instructions per second
- total number of electronic tubes – 4000
- total number of semiconductor diodes – 5000
- total number of ferromagnetic cores – about 200,000
- consumed power (without cooling) – about 35 kW
- the area necessary for normal operation – 170 sq. m.

- Main features: the instruction set of BESM-2 differed from that of BESM-1: several rarely used commands (for example, the absolute number transmission) were eliminated and some new commands were added. The hexadecimal notation of command coding was abandoned. Whereas there was only one instance of the BESM-1 computer, BESM-2 was manufactured serially and was widely applied in a number of research institutes in the USSR and abroad (in China).
- The computer is patented. There are numerous publications on the subject.