ZIT-151 is the name of the first series of mainframe computers manufactured in Bulgaria. It was manufactored by the ZIT factory in Sofia under licensing agreement with the Japanese company Fudjitsu. The machine was based on Facom-230-30 designed by the same company. The integration of the manufacturing process started with training of specialists, handing-over of the complete manufacturing documentation and ready-for-assembly components and cabinets imported from Japan. The machines were assembled in ZIT by using wire wrapping connection technology. This technology replaced soldering, i.e. electrical wire wrap tool was used to make connection between wire and pin (cold-welding). The computer series was based on semiconductor elements (diodes and transistors). By 1969 compatible prototypes were successfully manufactured. The manufacturing process was fully established with the help of measuring, control and testing equipmented imported from Japan. The actual production machines were based on components fabricated in Bulgaria. They were fabricated by the Semiconductor Factory in Botevgrad and the actual magnetic materials were replaced by other fabricated in Bulgaria or imported from GDR.

Computer Configuration   

• Input/Output Control Panel (typewriter/printer)
• Peripheral Input Devices - punch card reader and punch tape reader
• Peripheral Output Devices - card reader punch, printer
• External data storage devices - tape writers
• Standard components - power supply, CPU cabinet, magnetic memory (RAM), peripheral devices controller
• Alternating-current stabilizer - 25 kW electrical power output limit.

The series of machines was manufactured between 1967 and 1971. They were integrated in the Regional Computing Centers in Bulgaria. The project was under the direct guidance of Ivan Marangozov.

Features

ZIT 151 has capabilities equivalent or better than Facom 230-30. It uses some improvements from Facom 231 increasing the capabilities of the initial machine. The following execution speed was achieved for 10-bit integer arithmetic operations:

addition – 58.3 μs
subtraction - 82.5 μs
multiplication – 850 μs

While the following processing speed was achieved for floating-point instructions:

addition – 150 μs
subtraction - 200 μs
multiplication – 1400 μs

The magnetic-core memory had 2.2 μs access cycle. The memory capacity was increased compared to Facom 231 two times to the maximum 64KChar [2], where har(hartley) is a unit of information equal to log210 = 3,323 bit.

production cooperation

Acquisition of EIM than the original parts supply lease was produced by ZIT made in metal structures of cabinets. In the factory we have developed tools for the production of printed circuit boards, connectors, connecting cables and machining. Chemical processing, drilling and installation of the boards is done in ZIT. PCB soldering is performed on specialized machine purchased "tin wave". The cabinet OU (operational storage) and the PM (permanent memory) is made based on ferrite cores in ZZU (Plant memory devices) -  Veliko Tarnovo. The production of memory devices on magnetic tape (ZUML) are incorporated under license in the eponymous factory in Plovdiv.. Electric typewriter for input and output of EIM is produced in the factory typewriters - Plovdiv. Japanese card reader and reader tape were replaced with such devices chess company "Arrhythmia". Wide printing is imported from the US production company "Hewlett Packard" (5 pieces) and Polish production TURBOSNACK • fastest wide print DW 21 produced an English license.

Origins and Development

Licensed production of ZIT 151 in Bulgaria launch production of large Electronic computers. The implementation of this system of production provide the market with a computer, but also create footage for production and maintenance of such equipment, implement technology to produce unknown until then in Bulgaria, create new industrial capacities and livelihood in other places with the construction of factories, cooperated with factory computing machinery. When switching to the production of Electronic computers from a single system (EU) for the socialist camp in zit produced CPU EU 2020 EU system 1020, and supplied all produced Electronic computers in the socialist camp by EU sub disk storage (management plus 6 pcs. storage devices on magnetic disk (ZUMD) - 7 Mb or 29 Mb) and subsystems for storage devices on magnetic tape (control devices plus 6 pcs. peripheral storage devices on magnetic tape ZUML)). In Blagoevgrad produce mechanical structures in the plant for mechanical structures (CEM) in Ruse produce printed items in factory PCB for the entire production of DSO IZOT. In the town. Stara Zagora began production of disk drives, completing all Electronic computers produced in the socialist camp. In Pazardjik Factory magnetic disks are produced precisely crafted media - disk packs ZUMD. Electronics factory in Sofia specializes in the production of power devices such Electronic computers. In Plovdiv two plants - Plant Typewriter Factory storage devices on magnetic tape (ZUML) produce products intended only to supplement leaf Bulgarian peripherals plug into computers from a single system in the USSR, Hungary (EU 1010), GDR (German democratic Republic) (EU 1040) and Bulgaria (EU 1020).

Sources
     ((En)) Computer Museum. ZUML Fujitsu Facom 603B
     ((En)) Computer Museum. Historically, computer Fujitsu Facom 230 (Fujitsu 230-30). Picture of Data Center with 230-30

   3. http://bg.wikipedia.org/wiki/%D0%97%D0%98%D0%A2-151