In operating system design, what is SMP (Symmetric Multiprocessing) and how does it organize multiple processors sharing memory?

Introduction / Context:
As computer hardware evolved, manufacturers began to include multiple processors within a single system to improve performance and reliability. Symmetric multiprocessing, abbreviated as SMP, is one of the most common architectures used in general purpose operating systems. This question tests whether you understand the basic definition of SMP and how it differs from single processor systems or loosely coupled multiprocessor designs without shared memory.

Given Data / Assumptions:

• We are discussing multiprocessor computer systems.

• Processors may share memory and input or output devices.

• The operating system may schedule work on any available processor.

• The question is specifically about symmetric multiprocessing, not asymmetric designs or clusters.

Concept / Approach:
In symmetric multiprocessing, two or more similar or identical processors are connected to a single shared main memory and have equal access to I/O devices. The operating system is designed so that any processor can perform any task, including running kernel code. This symmetry simplifies scheduling because the kernel can treat all processors uniformly. In contrast, asymmetric multiprocessing assigns special roles to certain processors, and loosely coupled systems may have separate memories and operating systems. The correct option must clearly state that SMP involves multiple processors sharing memory and being treated equally by the operating system scheduler.

Step-by-Step Solution:
Step 1: Recall that in SMP, each processor is capable of running both user processes and kernel code, and no processor is dedicated only to specific tasks. Step 2: Note that all processors access the same main memory and I/O subsystem, which allows processes to be scheduled on any processor without migrating memory. Step 3: Recognize that the operating system is usually a single copy that manages all processors together rather than separate operating systems per processor. Step 4: Check each option for references to shared main memory, equal treatment of processors and common I/O and select the one that matches this description.

Verification / Alternative check:
To verify, imagine a typical multi core desktop or server machine running a modern operating system like Windows or Linux. Multiple cores share system memory, and the scheduler can run any process on any core. This is exactly the SMP model. The correct option should match that mental picture. Any option that says only one processor is active or that each processor has its own completely separate operating system does not reflect how SMP systems behave in practice.

Why Other Options Are Wrong:
Option B is wrong because it describes a single active processor, which is not multiprocessing at all. Option C is wrong because it refers to systems with separate operating systems and no shared memory, which are more like distributed systems or clusters. Option D is wrong because it confuses symmetric multiprocessing with symmetric cryptography, which is a completely different concept related to encryption algorithms rather than processor organization.

Common Pitfalls:
A common pitfall is to think that SMP simply means many processors without considering whether they share memory and are managed by one operating system instance. Another mistake is to confuse SMP with multicore processors inside a single chip; in reality, many multicore designs internally implement an SMP like model, but the term SMP is used more broadly for the overall architecture. Students should also be careful not to mix up SMP with asymmetric multiprocessing, where some processors are dedicated to special roles like I/O or operating system tasks.

Final Answer:
Thus, SMP is a system in which two or more identical processors share a common main memory and I/O, and the operating system treats them equally for scheduling.