Wikipedia
MINIMOP was an operating system which ran on the International Computers Limited (ICL) 1900 series of computers. MINIMOP provided an on-line, time-sharing environment (Multiple Online Programming, or MOP in ICL terminology). MINIMOP was named to reflect its role as an alternative to the MOP facilities of George 3, which required a more powerful machine.
MINIMOP would run on all 1900 processors apart from the low-end 1901 and 1902 and required only 16K words of memory and two 4 or 8 million character magnetic disks.
Each user was provided with a fixed size file to hold his data, which was subdivided into a number of variable sized subfiles. The command language could be extended with simple macros.
Batch facilities could be provided by simultaneously running George 2 on the same machine.