(acronym for Russian bystrodeistvuiushchaia elektronnaia schetnaia mashina, “high-speed electronic calculator”), the name of a series of digital computers developed at the Institute of Precise Mechanics and Computer Technology of the Academy of Sciences of the USSR. The BESM was one of the first modern general-purpose digital computers built with vacuum tubes and designed to solve scientific and engineering problems. One BESM was built and has been in operation since 1953.

The BESM has been improved: the electroacoustic mercury lines used as direct-access storage were replaced with cathode-ray tubes (1954) and then with ferrite cores (1956). In this form the machine is known as the BESM-1. (See Table 1 for main parameters of BESM computers.)

Thanks to modernization, the speed and operating reliability of the BESM (72 percent usable time with 8 percent downtime and 20 percent under maintenance) have increased. Various problems were solved on the BESM-1—for example, the orbits of 700 small planets of the solar system were calculated and cumbersome geodesic calculations were made. The design of the BESM-1 was revised for application to industrial technology, and in 1958 lot production of the tube-based BESM-2 was begun. It was already supplied with

a set of standard programs and with compiling and interpreting systems that made the programming process easier.

The BESM-3M and BESM-4 computers are semiconductor machines with a developed instruction repertoire (coinciding with that of the M-20 machine), a set of devices that ensure the solution of complex problems of mathematics, statistics, and accounting, and software for the programming process (set of subroutines, translators, and so on). The BESM-4, a modification of the BESM-3M, has a great capacity for solving economic planning problems.

The BESM-6, a semiconductor machine with an average operating speed of 1 million operations per second, a large memory capacity, and a developed system of input-output devices, was built for problems requiring a large number of computations. In its logic, diagram, and design execution, the BESM-6 reflects leading trends in the development of current computer technology and the automation of programming. The machine combines the work of individual units and exchange of information with external units. A multiprogram mode is envisioned which will increase the use efficiency of all units of the machine during the simultaneous solving of several problems. There is a hardware interrupt system, a “memory protection” circuit, and automatic address assignment. The control program, using these circuits, excludes the influence of some problems on others while they are being solved simultaneously, automatically distributes direct-access and external storage among the problems, and coordinates the work of external devices. A super high-speed memory, which is automatically controlled by a special circuit and which keeps the most frequently encountered statements in it, is a particular feature of the BESM-6. It is possible for operators at several control consoles equipped with alphanumeric printers to work simultaneously and independently, and they can be located at a distance and transmit information along communications channels.