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X - UWSpace - University of Waterloo

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apan. In mmy LAN's, communication is not very diable, for example, a message may be<br />

damaged, arrive out <strong>of</strong> order, or not amive at its destination at dl, so communication requires a<br />

lot <strong>of</strong> programming effort. ïherefore, some s<strong>of</strong>tware protocols for message passing systems such<br />

as Patallel Virtual Machine (PVM) and Message Passing Interface (MPT) are used to implement<br />

diable communication and sirnpler programming.<br />

PVM, which is more suitable for LAN based systems than MPI, provides an interface<br />

which links separate hosts. possibly <strong>of</strong> varying types. to create a single logicai host. so-called<br />

vinual machine. PVM allows a programmer to take virtually any network <strong>of</strong> M-based<br />

computen and mat them as a single parallel computer. "PVM has a somewhat lirnited message-<br />

passing subset, providing basic send and receive operations and some simple collective<br />

communications. but not providing the nch set <strong>of</strong> features that more formal message passing<br />

systems, like the MPI, provide. PVM does. however, provide a complete environment for pdlel<br />

computing, including the PVM console, and includes featms for dynamicaily adding and<br />

deleting machines from your own virtuai-machine configuration." (frorn Baker and Smith, 1996)<br />

A LAN limits the physical distance between processon to on the order <strong>of</strong> a few kilometen. To<br />

interconnect processon that are farther apart, a wide-area network (WAN) can be use&<br />

Performance Measurement in Parallel Computing<br />

Generally. the performance <strong>of</strong> parallel computation can be measured in two ways.<br />

speedup and efficiency. even thou* they depend on hardware, sohare and algorithms <strong>of</strong> solving<br />

a problem.<br />

The speedup S achieved by a paraIlel system is defined as the gain in computation speed<br />

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