Shared Memory MIMD machines
- All the PEs are connected to a single global memory and they all have access to it.
- Systems based on this model are also called tightly coupled multi processor systems.
- The communication between PEs in this model takes place through the shared memory.
- Modification of the data stored in the global memory by one PE is visible to all other PEs.
- The dominant representative shared memory MIMD systems are silicon graphics machines and Sun/IBM SMP ( Symmetric Multi-Processing).
Distributed Memory MIMD machines
- All PEs have a local memory. Systems based on this model are also called loosely coupled multi-processor systems.
- The communication between PEs in this model takes place through the interconnection network, the inter-process communication channel, or IPC.
- The network connecting PEs can be configured to tree, mesh, cube, and so on.
- Each PE operates asynchronously, and if communication/synchronization among tasks is necessary, they can do so by exchanging messages between them.
Shared Vs Distributed MIMD model
- The shared memory MIMD architecture is easier to program but is less tolerant to failures and harder to extend with respect to the distributed memory MIMD model.
- Failures, in a shared memory MIMD affect the entire system, whereas this is not the case of the distributed model, in which each of the PEs can be easily isolated.
- Moreover, shared memory MIMD architectures are less likely to scale because the addition of more PEs leads to memory contention.
- This is a situation that does not happen in the case of distributed memory, in which each PE has its own memory.
As a result, distributed memory MIMD architectures are most popular today
