Processor having Clock cycle of 0.25ns will have clock rate of
Answer: C
Correct answer: 4GHz
Clock rate is the reciprocal of the clock cycle time:
\[ \text{Clock rate}=\frac{1}{0.25\times10^{-9}\ \text{s}}=4\times10^{9}\ \text{Hz}=4\ \text{GHz} \]
A 0.5 ns cycle would give 2 GHz and a 0.125 ns cycle 8 GHz, which is what the other options correspond to.
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The relation PerformanceX = 1 / Execution TimeX shows that
Answer: A
Correct answer: Performance is increased when execution time is decreased
Performance is defined as the reciprocal of execution time, so the two move in opposite directions: halving the time doubles the performance. Any option in which both rise or both fall contradicts the reciprocal relation.
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If computer A execute a program in 10 seconds and computer B runs same in 15 seconds, how much faster is computer A than computer B
Answer: B
Correct answer: 1.5 times
Performance is the reciprocal of execution time, so the ratio of performances is the inverse ratio of times:
\[ \frac{\text{Performance}_A}{\text{Performance}_B}=\frac{\text{Time}_B}{\text{Time}_A}=\frac{15}{10}=1.5 \]
Computer A is therefore 1.5 times as fast as computer B.
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Computer A having clock cycle time of 250 ps and cycle per instruction of 2.0 for some programs, and computer B having clock cycle time of 500 ps and a cycle per instruction of 1.2 for same program. Which one is faster for this program
Answer: A
Correct answer: Computer A
Compare the time per instruction, which is the clock cycle time multiplied by the cycles per instruction:
\[ A: 250\ \text{ps}\times 2.0=500\ \text{ps} \qquad B: 500\ \text{ps}\times 1.2=600\ \text{ps} \]
A takes 500 ps per instruction against B's 600, so A is the faster machine by a factor of 600/500 = 1.2. Note that B has the better CPI and A the better clock; neither figure decides the question by itself.
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What is an exception condition in a computer system caused by an event external to the CPU known as ?
Answer: C
Correct answer: Interrupt
An interrupt is a signal raised by something outside the CPU - a device, a timer, an error condition - that causes the processor to break off what it is doing and attend to it. A halt stops the processor rather than diverting it, and a process is a program in execution.
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Whenever CPU detects an interrupt, what it do with current state ?
Answer: A
Correct answer: Save it
Before servicing an interrupt the CPU saves its current state - the program counter and the registers - so that when the service routine finishes it can resume the interrupted program exactly where it left off. Discarding the state would make return impossible, and finishing the current program first would defeat the purpose of interrupting.
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For two computers X and Y, if the performance of computer X is greater than the performance of computer Y, we have
Answer: B
Correct answer: PerformanceX > PerformanceY
The statement is simply restated in symbols: if X performs better than Y then its performance figure is the larger one. Since performance is 1/execution time, this is the same as saying X's execution time is the shorter of the two.
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If CPU and I/O interface share a common bus than transfer of data between two units is known as ?
Answer: C
Correct answer: Synchronous
When the CPU and the interface share a common bus they are driven by the same clock, so the transfer needs no separate timing agreement between them - that is what makes it synchronous. Asynchronous transfer is used precisely when the two units have independent clocks and must signal each other with control lines.
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Another type of multiple-CPU system is the
Answer: C
Correct answer: Clustered System
A clustered system is the other way of putting several CPUs to work: two or more complete computers, each with its own memory, joined over a network and sharing storage so that they act as one. A minicomputer and a supercomputer are classes of machine, not ways of combining CPUs.
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Valid and unimpeachable measurement of performance of any computer is
Answer: C
Correct answer: Execution time
Execution time is the only measure that cannot be gamed: it counts the whole job on the actual machine. A higher clock rate may be spent on more cycles per instruction, and an instruction set says nothing about how fast the instructions run, so neither is a reliable measure of performance on its own.
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