Loosely Coupled Systems
These systems do not distribute the global memory because shared memory concept gives rise to the difficulty of memory conflicts, which in turn slows down the implementation of instructions. Thus, to ease this problem, every processor in loosely coupled systems is having a great local memory (LM), which is not joint by any other processor. Therefore, such systems has multiple processors with their set of I/O devices and own local memory. This set of memory, processor and I/O devices makes a computer system. Thus, these systems are also known as multi-computer systems. These computer systems are related together via message passing interconnection network by which processes communicate by transient messages to one another. Hence every computer system or node in multicomputer systems have a separate memory, they are called as distributed multicomputer systems. These are also name as loosely coupled systems, meaning thatnodes have little coupling among them as shown in Figure .
Since local memories are accessible to the attached processor only, here no processor can access remote memory. Thus, these systems are also calles as no-remote memory access (NORMA) systems. Meaning passing interconnection network gives connection to each node and inter-node communication with message depends on the kind of interconnection network. For illustration, interconnection network for a non-hierarchical system can be common bus.