In personal computers, CPU clock speed is typically measured in which unit?

Introduction / Context:
One of the most common specifications you see when comparing processors is the CPU clock speed. This value indicates how many cycles per second the processor can perform, which roughly influences how many operations it can carry out in a given time. To correctly interpret CPU specifications and compare different processors, you need to know the unit used to express this clock speed. This question asks which physical unit is used to measure CPU speed in technical terms.

Given Data / Assumptions:

• The quantity being measured is CPU clock speed.
• The options are bytes per second (B/s), hertz (Hz), joules (J), and pixels per inch (PPI).
• We assume a standard modern processor where speed is shown as values like 3.0 GHz.
• We focus on the fundamental unit, independent of metric prefixes such as mega or giga.

Concept / Approach:
Clock speed describes how many cycles occur per second in a clock signal. The basic SI unit for cycles per second is hertz (Hz). CPUs often run at millions or billions of cycles per second, so practical specifications are given in megahertz (MHz) or gigahertz (GHz). For example, 3.0 GHz means 3.0 billion cycles per second. Bytes per second is a unit of data transfer rate, not clock frequency. Joules measure energy, not speed. Pixels per inch describes display resolution, not processor performance. Therefore, the correct unit to measure CPU clock speed is hertz (Hz).

Step-by-Step Solution:
Step 1: Recall what clock speed represents. Clock speed is the number of clock cycles a CPU completes in one second. Step 2: Identify the physical unit for cycles per second. The SI unit for cycles per second is hertz (Hz). Step 3: Connect this with common CPU ratings. Values like 2.4 GHz or 3.5 GHz are simply hertz scaled by a factor of 10^9. Step 4: Examine other options. Bytes per second measures data transfer rate over a network or bus, not internal CPU clock cycles. Step 5: Consider joules and pixels per inch. Joules are units of energy, while pixels per inch measure display density, and neither is related to CPU clock frequency. Step 6: Conclude that hertz (Hz) is the correct unit for CPU speed.

Verification / Alternative check:
Processor specification sheets from manufacturers such as Intel and AMD list clock speeds in GHz or MHz. Technical descriptions state that one hertz corresponds to one cycle per second, making gigahertz equal to one billion cycles per second. Network specifications, by contrast, use bits per second or bytes per second to describe throughput. Power consumption is measured in watts, and energy in joules. Display specifications use pixels per inch. This clear separation of units confirms that hertz is the unit for CPU clock speed and that the other options do not apply in this context.

Why Other Options Are Wrong:
Option A (Bytes per second (B/s)): This unit describes data transfer speed, such as Internet bandwidth or disk read speed, not CPU clock frequency. Option C (Joules (J)): Joules measure energy, for example the energy consumed over time, not processor speed. Option D (Pixels per inch (PPI)): PPI measures screen resolution or print density, and does not relate to CPU operations per second.

Common Pitfalls:
Students may focus on a familiar abbreviation like GHz without realising that G in GHz stands for giga, a metric prefix, and that the underlying unit is hertz. Others might confuse data rate units such as megabits per second with CPU speed because both use the concept of per second. To avoid confusion, remember that clock speed is about cycles of an internal clock, so it uses the hertz unit, while data transfer speeds use bits or bytes per second, and display qualities use pixels per inch.

Final Answer:
CPU clock speed in personal computers is measured in Hertz (Hz), typically expressed as MHz or GHz.