Computer System Architecture Questions and Answers

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.

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.

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.

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.

Answer: B

Correct answer: Performance_X > Performance_Y

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.

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.

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.

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.

Answer: A

Correct answer: SPEC benchmark

SPEC - the Standard Performance Evaluation Corporation - publishes the suites of CPU-intensive integer and floating-point programs used to compare machines. The other three names are not benchmark suites.

Answer: A

Correct answer: hot standby mode

In asymmetric clustering one machine runs the application while the other does nothing but monitor it, ready to take over the instant it fails. A machine kept powered and ready in this way is in hot standby; plain standby would not imply that it is already running and watching.