THE multiprogramming system: It was a layered multiprogramming system built by E. W. Dijkstra in 1968 at Technische Hogeschool Eindhoven in the Netherlands. It was a batch system for a computer Electrologica X8 having 32K of 27 bit words.
Here are the different layers of THE multiprogramming layered system:
Layer 0: Layer 0 was for handling processor allocation, multiprogramming of CPU, and to switch between processes.
Layer 1: Layer 1 was used for memory management and allocating space for processes.
Layer 2: Layer 2 was used for inter process communication and user-process communication.
Layer 3: Layer 3 was used for management of I/O devices.
Layer 4: Layer 4 was used for user programs.
Layer 5: Layer 5 was used for the user.
MULTICS (Multiplexed Information and Computing Service): Instead of layers, MULTICS used concept of concentric rings. A system call needs to be made by the procedure of an outer ring to a procedure in an inner ring. IN MULTICS, procedures are referred to as segments. The whole operating system is a part of address space of each user process.