KR1858VM1 - Rare plastic clone of famous 8-bit CPU ZILOG Z80.
MADE IN USSR by scientific production association "Electronika" (USSR, Voronezh city) in 1991.

Great item for chip collectors !!!

For more information, please visit -
cpu-world.com/CPUs/Z80/MANUF-USSR.html
or here - speccy.info/Zilog_Z80
 

Some history:

Development of Zilog Z80 microprocessor was based on Intel 8080/8085 series, 
therefore Z80 is backward 8085 compatible by command set and machine code, 
it can execute any programs written for 8085. 
For example, CP/M-80 OS can be run on 8080, 8085, Z80. 
But forward compatibility is not always achieved, mainly because of additional commands, 
registers, and other new features that are present in Z80.

As 8080/8085 processors, Z80 was manufactured in 40-pin dual inline package. 
There are modifications that differ by clock frequency. 
Address lines, in contrast to 8085 are not multiplexed, 
so the number of management lines and types of interrupts is reduced. Interrupts can be masked and non-masked.

Command set of Z80 is compatible with 8085, though command mnemonics are different. 
There are additional commands for block transfer, checking/setting of separate operand bits, 
working with packed binary-decimal code, organising cycles, performing relative transitions.

Z80 microprocessor does not have clock generator as 8085 does and needs an external chip to do this. 
Having only one input for masked interrupt requests it causes all devices connected to processor to form one priority chain. 
All support chips released by Zilog are called “Z80 - chip type”, for example Z80-PIO, Z80-UART and others. 
 
This processor was used in Tandy Radio Shack TRS-80 PC. TRS-80 computer, created by Steven Leyninger, 
was sold together with monitor, keyboard, tape recorder, and tapes that contained CP/M-80 OS and additional software. 
In September 1977 the computer hit the market and had sales of 10 thousand a month during the whole next year. 
Later, selling a computer assembled and with all needed components preincluded became essential.

Besides TRS-80, Z80 processor was used in ZX80/81 and ZX-Spectrum computers made by Sinclair Radions Inc. 
They were spreading at such fast pace that in fact became the standard for 8-bit personal computer systems, 
as IBM PC/XT/AT for 16-bit ones. 
ZX81 computer had been manufactured until 1983 when it's price in USA reached $50 and it became unprofitable. 
Spectrum and it's clones are still popular between radio-amateurs

CPU from the Old Stock, in working order.