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"Carat" computer system MP4.21
The first "Carats". There were 15 modifications of computer "Carat". The unified modifications of "Carat" used at more than 60 system types.
The computers of the series "Carat" are designed for solving of tasks in composition of the systems for data processing, operation, and control. Vilen Nikolayevich Plotnikov is the General constructor of computers of the series "Carat". 1973

"...The "Carat" family of installed computers, developed under management of Vilen N.Plotnikov, was the first in the Soviet Union broadly used in Navy radio-electronic systems. The important indicator of computer perfection is mean-time-between-failures which consisted more than 2 000 hours (almost 100 days) for the first "Carats", and more than 10 000 hours (almost 5 years) for the next modifications. At the beginning of 1970-s, these figures seemed to be fantastic. Just such a very reliability is required for the computers, which are adjusted on ships and submarines and are operated under the conditions of high humidity, great temperature fluctuations, and weight overloading . "Carats" passed the exams: many computers had operated on board for 10-15 years without a single failure!
The first "Carats" were built in 1969-1972. In all, 15 computer modifications and over 5 mln. programm commands are developed. More than 1500 models are manufactured. The unified modifications "Carat KM" are installed in more than 60 systems. Within these years, more than 2 000 computers were manufactured at the plants of Ukraine and Russia! They were used in systems of sixty modifications..."