The Radio-86RK was the second DIY computer featured in Radio magazine, in an edition published in 1986. It was more popular than the Micro-80 because it was much simpler (29 IC's, i8080 @1.78 MHz with i8257 and i8275 based CRT terminal). Many factories started production of home computers based on this design (such as the Apogey BK-01, Mikrosha, Krista, Partner 01.01, and the Spektr-001). These computers had limited compatibility with the original software, although their schematics were very close to the original.
The Radio-86RK was the successor of the "Micro-80" - the electric scheme and BIOS code were published in the local radio electronics-fans magazine “Radio” in June 1986. The name seems to be derived from the name of the magazin and the year. RK may be a short form of Do It Yourself Kit. The circuit count was reduced from 200 to about 29 - so it was easier to built. That might be the reason why the Radio-86RK became so very popular that a lot of clones (some even industrial manufactured) were built. It looks like the whole computer family could be called "RK-86" compatible.
According to Kirill Kukarkin the 8-bit CPU K580VM80 used for the Radio-86 is a clone of Intel 8080A. It has 16/32 Kb RAM, 4Kb ROM, 25x80 monochrome display (TV) and used tape recorder as external ROM. Based on Radio-RK schematic the following PCs were industry produced: Microsha, Krista, Electronica KR01…04 with a insignificant modification in electric scheme and BIOS. The additional adapters designed in 1987 – 1992 allowed to produce sound, add color display, attach FDD, attach ROM modules.
The computer was not produced commercially. For the assembly of the computer required to acquire the necessary electronic components, to produce two printed circuit boards and mount them on all components. Furthermore, it was necessary to help the programmer write firmware into two chip erasable ROM , and make power supply unit, a keyboard and the computer case. Computer to use as a monitor household television connected via the video input. Many domestic TVs do not have a video input and require the installation of special module  or revised scheme  .
"Radio-86RK" was not the first amateur computer design. In the early 80's magazine "Radio" has published a description of amateur computer processor KR580IK80. It was a "Micro-80" , consisting of several modules and employs about 200 chips. The computer was difficult in assembling and adjusting. Because of its complexity, but also because of the almost complete absence of chips in the free market, "Micro-80" were collected only a few enthusiasts. "Radio-86RK" partially compatible with the "Micro-80", so that the program as adapted from the old to the new model, and vice versa.
Scheme "Radio-86RK" included only 29 chips, so it was easier to repeat. However, in the retail chips were a scarce commodity and are only available in limited Moscow and major cities of the USSR  . Unavailability of the video chip KR580VG75 produced in very limited numbers, led to the development of the scheme replaces it with 19 more chips available  constructed similarly display unit "Micro-80".
Because almost all letters addressed to the Editor of "Radio" in response to the publication of a series of articles about the "Radio-86RK 'amateurs drawn attention to the difficulty of completing the acquisition, the editors turned to the industry with a proposal to start producing sets-radiokonstruktorov  . By the end of the 80 manufacturing enclosures, keyboards and motherboards for "Radio-86RK", as well as trade in components implemented numerous cooperatives.
Processor: K580IK80A (in the late Soviet nomenclature - KR580VM80A ) - Soviet analogue i8080A or more perfect KR580VM1 , clocked at 1.78 MHz . To simplify the scheme used one clock source for the CPU and the video. Since your video demanded a strictly defined frequency, CPU clock speed has been lowered from the nominal 2.5 MHz processor. Later in the magazine was published to finalize the details of the seven that make up a separate clock for the video, allowing the processor to raise the frequency of the nominal value. 
RAM : in the original version - 16 KB on chips DRAM K565RU3 . Could also be applied K581RU4, K565RU6 (4116) or rejection, "half" and "quarters" K565RU5 (4164). The design allows to increase the memory up to 32 KB, installing additional memory chips "second floor." There are two versions of "The Monitor" - the amount of memory and 16KB 32KB. The upper half of the address space is used to control internal computer devices (IO team VM80 not used).
ROM : 2 KB - erasable ROM or K573RF2 K573RF5 (2716) which placed the "Monitor".
Video: text mode only 25 lines by 64 characters. Used "controller alphanumeric terminal" KR580VG75 together with "controller direct memory access" KR580VT57 (i8257). The latter is also used for regeneration of the dynamic memory. CG characters for the ROM (K573RF1, 1 KB). Hardware cursor formed KR580VG75.
All Very kindly donated by Alexander Demin. His blog and details of his projects can be seen at http://demin.ws/english/
An emulator from Alender Demin is on line so that you can play with it, it is in Russian but you can soon sort it out at http://rk86.ru/ and a Catalog of programs for Radio-86RK can be found at http://rk86.ru/catalog/
Manufacturer: Soviet Bloc
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