IPA IP 2021 Question 90

A question IPA Japan published in 令和3年度 ITパスポート試験公開問題問90, translated into English. ITPEC is based on the same exams.

Which of the following is an appropriate explanation concerning the clock of a CPU?

a)The data transfer speed between a peripheral device connected via USB and the CPU is determined by the frequency of the clock.b)The shorter the interval of the clock, the more time it takes to execute instructions.c)The clock records the storage location of the instruction to be executed next.d)The clock adjusts the timing of instruction execution.

Explanation

The clock adjusts the timing of instruction execution — the clock is the periodic signal that paces and synchronises the CPU's operations.

The CPU's circuits work in step with a clock signal: each step of fetching, decoding and executing an instruction starts on a clock pulse. The number of pulses per second is the clock frequency, in Hz. With the same CPU design, a higher frequency means a shorter interval between pulses, so instructions finish sooner.

Answer (d)

Why not others:

•(a) — the speed of a USB transfer is set by the USB standard (for example 480 Mbit/s for USB 2.0) and the device, not by the CPU's clock frequency
•(b) — reversed: a shorter clock interval is a higher frequency, which makes instruction execution faster, not slower
•(c) — keeping the address of the next instruction to be executed is the job of the program counter, a register in the CPU

Key rule: The clock sets the CPU's pace; the program counter holds the address of the next instruction.

Computer Component · AI-written, may contain errors

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This question comes from the past questions IPA Japan publishes, translated into English by ITPEC Practice. ITPEC Practice is an independent study tool and is not affiliated with IPA or ITPEC. See the original paper (PDF) or Report an issue.