In Unix System V, when multiple swap devices are available, what scheme does the kernel follow when choosing a swap device for paging or swapping?

Introduction / Context:
Unix System V introduced support for multiple swap devices to improve performance and flexibility in memory management. When more than one swap device is configured, the kernel must choose which device to use for swapping or paging operations. This question asks you to recall the strategy the Unix System V kernel uses to select among several swap devices.

Given Data / Assumptions:

• The system may have multiple swap devices configured.
• The kernel aims to distribute swapping activity sensibly across them.
• The question refers specifically to Unix System V behaviour.
• No numeric calculations are needed.

Concept / Approach:
To avoid overloading a single swap device and to exploit parallelism, Unix System V spreads swap operations across devices. The strategy documented for this system is a round robin scheme, where the kernel chooses devices in cyclic order. This roughly balances the load without requiring complex dynamic measurement of device performance. The approach is simple and fair, aligning with the classical round robin idea used in many scheduling contexts.

Step-by-Step Solution:
Step 1: Recall that multiple swap devices are meant to provide performance gains via parallelism and load distribution. Step 2: Consider common selection strategies: always first, random or balanced in some way. Step 3: Recognise that always using the first device would waste the potential of additional devices. Step 4: Note that random selection is possible but not typical for deterministic operating system kernels. Step 5: Identify round robin selection as a simple, deterministic load distribution method and choose the option that mentions it explicitly.

Verification / Alternative check:
Interview question collections and technical notes on Unix System V memory management explicitly state that the kernel follows a round robin scheme for choosing a swap device among multiple swap devices. This aligns with the general design goals of balancing load without heavy overhead and confirms that the correct answer is the option indicating a round robin scheme.

Why Other Options Are Wrong:
Option B is wrong because always using only the first device defeats the purpose of configuring multiple swap areas. Option C, random selection, is not commonly cited in documentation and would lead to unpredictable behaviour. Option D ties device selection to the user identity, which has no natural relation to swap performance and is not how Unix System V is described in technical references.

Common Pitfalls:
A common error is to assume that all resource allocation decisions are made strictly by priority or load measurement. In reality, simple schemes such as round robin are often used because they are easy to implement and provide adequate fairness. Another pitfall is ignoring the specific system mentioned in the question; behaviour can differ between Unix variants, so it is important to pay attention to the reference to Unix System V.

Final Answer:
Unix System V uses a round robin scheme to choose among multiple swap devices, distributing swap activity across them in turn.