Some Computer Organizations and Their Effectiveness

A hierarchical model of computer organizations is more "macroscopic" view, yet without reference to a developed, based on a tree model using request/service type reparticular user environment. Clearly, any such effort sources as nodes. Two aspects of the model are distinguished: logical m ustb shr limitedtim anyasc somefoft andphysical. ~~~~~~~must be sharply limited In many aspects; some of the and physical. mr infcn r sflos General parallelor multiple-stream organizations are examined more significant are as follows. as to type and effectiveness-especially regarding intrinsic logical 1) There is no treatment of I/O problems or I/O as a difficulties. limiting resource. We assume that all programs of interThe overlapped simplex processor (SISD) is limited by data est will either not be limited by I/O, or the I/O limitadependencies. Branching has a particularly degenerative effect. * w The parallel processors [single-instruction stream-multipletionsawill ap eul to all c e me mory condata stream (SIMD)J are analyzed. In particular, a nesting type figurations That is, the I/O device sees a "black box" explanation is offered for Minsky's conjecture-the performance of computer with a certain performance. We shall be cona parallel processor increases as log M instead of M (the number of cerned with how the computer attained a performance data stream processors). potential, wThile it may never be realized due to I/O conMultiprocessors (MIMD) are subjected to a saturation syndrome siderations. based on general communications lockout. Simplified queuing models We t t indicate that saturation develops when the fraction of task time spent 2) \\e make no assessment of particular instruction locked out (L/E) approaches 1!, where n is the number of processets. It is assumed that there exists a (more or less) ideal sors. Resources sharing in multiprocessors can be used to avoid set of instructions with a basically uniform execution several other classic organizational problems. time-except for data conditional branch instructions