In memory management, why do operating systems use paging instead of requiring each process to occupy one large contiguous block of physical memory?

Introduction / Context:
Memory management is one of the core responsibilities of an operating system. Early systems often tried to allocate a single contiguous region of physical memory for each process, but this approach led to serious fragmentation and inflexibility. Paging is a widely used solution that divides both virtual and physical memory into fixed size blocks. This question asks why paging is used and what benefits it provides over simple contiguous allocation schemes.

Given Data / Assumptions:

• Processes need memory for code, data and stack.

• Physical memory is limited and must be shared among many processes.

• Without paging, each process might require one large contiguous block of physical memory.

• Paging divides virtual memory into pages and physical memory into frames of the same size.

Concept / Approach:
With paging, the operating system can allocate physical memory to a process in any set of free frames, even if these frames are scattered across the address space. This noncontiguous allocation greatly reduces external fragmentation because any free frame can be used for any page. It also simplifies memory management because all frames are the same size and the allocation problem becomes more like managing a pool of identical blocks. The mapping between virtual pages and physical frames is stored in page tables, allowing each process to see a continuous virtual address space even though the underlying physical memory is fragmented.

Step-by-Step Solution:
Step 1: Recall that without paging, processes may need large contiguous regions of memory, and over time holes of unused memory appear between allocated regions, leading to external fragmentation. Step 2: Understand that paging divides virtual memory into pages and physical memory into frames of equal size, so any page can be placed in any frame. Step 3: Note that a process can still see a logical contiguous address space while its pages are scattered across physical memory. Step 4: Compare each option and choose the one that states that paging enables noncontiguous allocation, reduces external fragmentation and simplifies memory management.

Verification / Alternative check:
As an alternative check, imagine a system where many processes start and stop over time. If each requires a contiguous region, memory quickly becomes fragmented into many small holes that are too small for new large processes. Paging solves this by allowing a process to be placed wherever free frames exist, even if they are not adjacent. This mental model matches the explanation in the correct option and is widely reflected in operating system textbooks that describe the advantages of paging.

Why Other Options Are Wrong:
Option B is wrong because paging does not remove the use of RAM; it is a way to manage RAM more flexibly and may cooperate with virtual memory to move pages between RAM and disk. Option C is wrong because paging is not a printer technology; it is directly related to main memory allocation. Option D is wrong because paging is most useful when multiple processes share memory; it is not disabled in multiprogramming systems but rather used specifically to support them.

Common Pitfalls:
A common pitfall is to think that paging removes all kinds of fragmentation. In reality, paging eliminates external fragmentation, but internal fragmentation can still occur inside individual pages if the process does not use the entire page. Another mistake is to assume that paging always makes programs faster; although it simplifies allocation, it can introduce overhead in address translation and page table management. Keeping in mind that the main motivations are flexible noncontiguous allocation and reduced external fragmentation will help you answer similar questions correctly.

Final Answer:
Therefore, paging is used because it allows noncontiguous allocation of physical memory frames, reduces external fragmentation and simplifies memory management for processes.