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'''Design Goals'''
The most common goals in a Computer Architecture include revolve around the tradeoffs between cost and performance (i.e. speed), although other considerations, such as size, weight, and weightpower consumption, may be a factor as well.
1. Cost
Computer retailers describe the performance of their machines in terms of clock speed (usually in MHz or GHz). This refers to the cycles per second of the main clock of the CPU. However, this metric is somewhat misleading, as a machine with a higher clock rate may not necessarily have higher performance. Most modern CPUs are capable of executing multiple instructions per clock cycle (see [[superscalar]]), which can have a dramatic effect on how quickly a program can run, as can other factors, such as the mix of [[functional unit]]s, [[computer bus|bus]] speeds, available memory, and the type and order of instructions in the programs being run.
Better metrics can be obtained by [[benchmark]]ing, which attempts to take all these factors into account by measuremeasuring the time that the system takes to run through a series of provided programs. This can be used to obtain an average throughput for the system. Even still, benchmarksbenchmarking may not clearly show whichthat one of two systems is clearly better, since one system may, for example, be optomized to handle scientific applications, and another may be optomized to play popular video games.
"Another important performance consideratin is [[Interruptinterrupt latency]]", which is the guaranteed maximum response time of the softwaresystem to an event such as the click of a mouse or the reception of data by a modem. This number is also affected by a very wide range of design choices. Computers that control machinery usually need low interrupt latencies, because the machine can't, won't or should not wait. For example, computer-controlled anti-lock brakes should not wait for the computer to finish what it's doing - they should brake.
Since cost is usually constant, the variables usually consist of latency, throughput, convenience, storage capacity and input-output. The general scheme of optimization is to budget the different parts of the computer system seperately. In a balanced computer system, the data rate will be constant for all parts of the system, and cost will be allocated proportionally to assure this. The exact formsform of the trade-offscomputer system will depend on whether the computerconstraints systemand isgoals beingit was optimized to minimize latency or maximize throughputfor.
Also see [[CPU design]].
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