In CPU scheduling, what do the performance metrics turnaround time and response time mean for a process from submission to completion and first reply?

Introduction / Context:
When we evaluate a CPU scheduling algorithm in an operating system, we often talk about quantitative performance metrics. Two of the most important metrics are turnaround time and response time. These terms are widely used in exam questions, interviews and real performance tuning, so it is important to know exactly what they measure and how they differ, especially for batch jobs versus interactive processes.

Given Data / Assumptions:

• We are dealing with processes or jobs submitted to a CPU scheduler.

• Each job is submitted at some time, may wait, execute and then finish.

• Interactive jobs may produce a first visible response before they finally complete.

• The question asks specifically for the meaning of turnaround time and response time.

Concept / Approach:
Turnaround time is a completion oriented metric. It measures how long a job takes from the moment it enters the system until it finishes all its work. Response time is an interaction oriented metric. It measures how long it takes the system to start responding to a user request, not how long it takes to finish the entire job. The correct option must clearly capture these ideas and must not confuse them with queue waiting time or with pure CPU burst time.

Step-by-Step Solution:
Step 1: Recall that turnaround time is defined as completion time minus arrival time. It includes waiting time, CPU execution time and any other delays. Step 2: Recall that response time is defined as the time from arrival of a request until the first response is produced, for example the first character of output or the first GUI update. Step 3: Compare each option with these standard definitions and eliminate any option that talks only about ready queue waiting time or only CPU burst length. Step 4: Select the option that states that turnaround time covers the entire life of the job and response time covers the delay before the first reply is given to the user.

Verification / Alternative check:
As an extra check, imagine a long interactive program such as a compiler running in an integrated development environment. The response time might be short because the editor window appears quickly, but the turnaround time of a full build may be long. Any correct definition must allow these values to be different. Also, textbooks on operating systems consistently define turnaround time as a full completion measure and response time as a first reaction measure, so the correct option should echo that terminology very closely.

Why Other Options Are Wrong:
Option B is wrong because it says that turnaround time is the time spent only in the ready queue, which ignores CPU execution and input or output delays. It also reduces response time to CPU execution time only, which is not accurate. Option C is wrong because turnaround time and response time are often different, especially for interactive and time sharing systems. Option D is wrong because these metrics do not directly measure CPU speed or memory size; they are time intervals seen by jobs and users, not hardware specifications.

Common Pitfalls:
A common pitfall is to confuse turnaround time with waiting time, even though waiting time is only a part of turnaround time. Another frequent mistake is to assume that response time is the whole program run time, whereas it is only the delay before the first response. Students may also assume that response time does not include any queue delay, but it actually includes all delay from submission until first response. Being clear about whether we are talking about first reaction or final completion helps avoid these misunderstandings in exam questions and in practical performance analysis.

Final Answer:
Thus, turnaround time is the total time from job submission to completion, while response time is the time from submission until the system produces the first response to the user.