(a) The cycle time of a microprocessor is the time for one complete clock cycle.
ID: 3853620 • Letter: #
Question
(a) The cycle time of a microprocessor is the time for one complete clock cycle. For example, if the clock frequency of a microprocessor is 2 million cycles per second (2 MHz), then each cycle takes 500 ns (500 billionths of a second). Compare the cycle time of a microprocessor running at 2 MHz with one running at 50 MHz, 500 MHz, and 2 GHz. (b) If a certain 80 times 86 instruction requires four clock cycles to execute, how long does the instruction take to execute if the processor clock speed is 25 MHz? Repeat for a clock speed of 800 MHz.Explanation / Answer
a) 2MHz:
2*(10^6) clock cycles per second
so each clock cycle takes = 1/(2*(10^6)) seconds = 500ns
50MHz
50*(10^6) clock cycles per second
so each clock cycle takes = 1/(50*(10^6)) seconds = 20ns
500MHz
500*(10^6) clock cycles per second
so each clock cycle takes = 1/(500*(10^6)) seconds = 2ns
2GHz
2*(10^9) clock cycles per second
so each clock cycle takes = 1/(2*(10^9)) seconds = 0.5ns
b) Given instruction takes 4 clock cycles
1. In 25MHz processor each clock cycle takes 40ns so given instruction takes 4 clock cycles so
total time for given instruction using 25MHz processor = 4*40 =160 ns
2. In 800MHz processor each clock cycle takes 1.25ns so given instruction takes 4 clock cycles so
total time for given instruction using 800MHz processor = 4*1.25 =5 ns
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