Concurrent Systems

;SPM_quot;What is Concurrency?;SPM_quot; Concurrency is the property of a system that more than one thing is (apparently) happening at the same time. In the software world, we commonly find 3 types of concurrency: There are three challenges with concurrent systems: What distinguishes distributed systems from parallel systems? Firstly, communication is characteristically much more expensive between distributed processes that between parallel ones. This usually rules out models based on simulated shared memory. Secondly, hardware in a distributed system is generally fault tolerant. The network may partition, processing nodes fail, and yet a distributed algorithm may successfully complete. Note that this is only a potential for greater reliability. The economics of disk prices versus processor and network proces meant that many so-called distributed filesystems evolved in the 1980s that were less relaible than centralised ones, since the separation of application/client from server/disk via a network simply introduced more points of failure than a centralized system would have.