In operating systems, what is a major drawback of MVT (Multiprogramming with a Variable number of Tasks) variable-partition memory management?

Introduction / Context:
Early operating systems used different strategies to support multiprogramming, including MFT (Multiprogramming with a Fixed number of Tasks) and MVT (Multiprogramming with a Variable number of Tasks). MVT uses variable sized partitions in main memory so that each process can be allocated just enough contiguous space for its code and data. While this improves flexibility compared to fixed partitions, it introduces its own drawbacks. Understanding the downside of MVT is important when comparing memory management schemes.

Given Data / Assumptions:

• MVT uses variable sized contiguous regions of memory for processes.
• Processes arrive and depart over time with different memory sizes.
• Free memory is managed as a set of available holes.
• The question asks for a major drawback of the MVT approach.

Concept / Approach:
Under MVT, when a process terminates or is swapped out, it leaves behind a hole in memory. New processes are placed into holes according to placement algorithms such as first fit, best fit, or worst fit. Over time, as different sized processes are loaded and removed, free memory becomes fragmented into many small noncontiguous pieces. Even if the total free memory is large enough for a new process, there may not be a single contiguous block big enough to satisfy its request. This phenomenon is external fragmentation and is the key drawback of MVT. Compaction can reduce fragmentation but is expensive.

Step-by-Step Solution:
Step 1: Recall that in MVT each process is allocated a contiguous region whose size equals its memory requirement.Step 2: When processes finish or are removed, they free their regions, leaving holes of varying sizes scattered throughout memory.Step 3: As more processes of different sizes arrive, it becomes difficult to find a single large contiguous hole even when the total free memory is sufficient.Step 4: This scattered arrangement of free space is known as external fragmentation and is a major cause of allocation failures in MVT.Step 5: The operating system can attempt compaction to merge holes, but moving many processes in memory is time consuming and can significantly degrade performance.

Verification / Alternative check:
Operating systems textbooks describe MVT as an improvement over fixed partition schemes because it allows variable process sizes and better utilization initially. However, they also emphasize that MVT is vulnerable to external fragmentation. Diagrams often show memory after several allocations and deallocations, with many small holes that cannot be easily used. The recommended remedy is compaction, which confirms that fragmentation is a central drawback of MVT.

Why Other Options Are Wrong:
Option B is incorrect because the entire purpose of MVT is to support multiple processes in memory simultaneously; it does not disable multiprogramming. Option C describes a limitation of fixed partition schemes such as MFT, where partitions are fixed in size, not of MVT with variable partitions. Option D is wrong because MVT is designed for user processes as well as system processes; it is not restricted to the kernel.

Common Pitfalls:
Students may confuse internal and external fragmentation and sometimes assume that variable partitions eliminate waste. In reality, while MVT reduces internal fragmentation compared to fixed partitions, it introduces serious external fragmentation because of varying process sizes. Another pitfall is to think that compaction is a trivial solution, but in large systems frequent compaction can itself consume significant CPU and I or O resources.

Final Answer:
A major drawback of MVT is that it suffers from external fragmentation, where free memory becomes scattered into small holes and may require expensive compaction to reuse effectively.