The CPU is a very complex piece of circuitry. For those interested in writing fast software, a natural question to ask is, "How does the processor execute statements, and how do we measure how long they take to execute?" As you might expect, the second Pascal statement above takes quite a bit longer to execute than the first. Likewise, multiplying I by five and then adding two and storing the result back into I takes time. Moving a copy of J into I takes a certain amount of time. Of course, on real computer systems, operations do not occur instantaneously. It wouldn't do, for example, to execute the statement I:=I*5+2 before I :=J in the following sequence:Ĭlearly we need some way to control which statement executes first and which executes second. ![]() This means that the computer executes commands in a prescribed order. On Von Neumann machines, like the 80x86, most operations are serialized. Art of Assembly: Chapter Three-2 ģ.2 - System Timing 3.2.1 - The System Clock 3.2.2 - Memory Access and the System Clock 3.2.3 - Wait States 3.2.4 - Cache MemoryĪlthough modern computers are quite fast and getting faster all the time, they still require a finite amount of time to accomplish even the smallest tasks.
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