Introduction Distributed System (2)

Introduction Part 2 .. (English edition)

Reasons and Properties  for Distributing Systems,

Distributing Systems is A collection of processors executing independent instruction streams that communicate and synchronize their actions. Communication may be done via messages or shared memory. and  includes multi-process and multithreaded programs running on a monolithic multiprocessor hardware.

Reasons for Distributing Systems

• The need to share data across remote geographies
• Online Encyclopedia Britannica is accessed by users all over the world
• Computer users in different geographies send messages to each other
• Replication of processing power
• Independent processors working on the same task
• Distributed systems consisting of collections of microcomputers may have processing power of a large supercomputer 
• Use of heterogeneous components
• Compute-intensive sub-tasks of a problem are run on powerful computers
• Less resource-demanding sub-tasks run on less powerful computers
• More efficient use of resources
• Cost of hardware and management
• A collection of cheap computers may be less expensive than one large supercomputer
• Small simple computers may be easier to manage than one large one
• Administrative/functional issues
• Payroll database is separate from registrar’s database
• Each is managed according to the needs of the organization
• Each is equipped with hardware that answers the needs of an organization
• Resilience to failures
• If one component fails, others can proceed with work on the task
• Scalability
• The system can be extended by adding more components (i.e., WWW)

Properties for Distributing Systems

• Heterogeneity : Systems consist of heterogeneous hardware and software components
• Concurrency : Multiple programs run together
• Shared data  : Data is accessed simultaneously by multiple entities
• No global clock : Each component has a local notion of time
• Interdependencies : Independent components depend on each other