M series (computer)

M-20, M-220 and M222 were a range of general-purpose computers designed and manufactured in the USSR.
These computers were developed by the Scientific Research Institute of Electronic Machines (NIIEM) and built
at Moscow Plant of Calculating and Analyzing Machines (SAM) and 
the Kazan Plant of Computing Machines (under the Ministry of Radio Industry of the USSR).
Operating systems.
The operating system provided batch processing and simultaneous execution, subsequently enhanced to provide a multitasking mode.