In operating system design, what is the difference between a microkernel and a macro kernel or monolithic kernel?

Introduction / Context:
Kernel architecture strongly influences system reliability, extensibility and performance. Two contrasting designs are the microkernel approach and the macro kernel or monolithic kernel approach. Understanding the division of responsibilities between kernel space and user space in each design is important for analysing operating system structures. This question asks you to explain the difference between these two kernel types.

Given Data / Assumptions:

• The kernel executes in a privileged mode of the processor.
• System services may run either in kernel space or user space.
• Microkernels aim to minimise what runs in kernel mode.
• Monolithic or macro kernels include many services in the kernel.

Concept / Approach:
In a microkernel design, the kernel is kept as small as possible. It usually provides only essential mechanisms such as low level address space management, basic thread management, scheduling and interprocess communication. Higher level services such as file systems, network stacks and many device drivers run as user space servers that communicate with clients and each other via message passing. In a macro kernel or monolithic kernel, many of these services and drivers are compiled into a single large kernel binary, all running in kernel mode and sharing a common address space. This design can achieve high performance but may be more vulnerable to bugs in any kernel component.

Step-by-Step Solution:
Step 1: Identify the fundamental goal of a microkernel: minimal trusted code running in kernel mode. Step 2: List typical microkernel responsibilities: address space management, scheduling and interprocess communication primitives. Step 3: Recognise that services such as file systems and device drivers are pushed out to user space servers in a microkernel architecture. Step 4: Contrast this with a monolithic kernel, where those services are part of one large kernel image and execute in kernel mode. Step 5: Choose the option that clearly describes this division between minimal and extensive kernel responsibilities.

Verification / Alternative check:
Descriptions of microkernel based systems, such as Mach or Minix, emphasise that only core mechanisms reside in the kernel, with most services implemented as user space servers. In contrast, traditional Unix and many earlier Linux designs are described as monolithic, with file system, network and driver code inside the kernel. These sources match the explanation in the correct option and do not mention hardware chips or purely size based distinctions as defining characteristics.

Why Other Options Are Wrong:
Option B wrongly claims that microkernels are always larger in size and restricted to single processor systems, which is not true and misses the conceptual point. Option C confuses kernels with hardware chips and software libraries, which is not how kernel architectures are categorised. Option D says there is no conceptual difference, which is clearly false given the extensive literature contrasting microkernel and monolithic approaches.

Common Pitfalls:
A typical misunderstanding is to equate microkernel with microcomputer or to interpret micro only in terms of physical size, rather than minimal functionality in kernel mode. Another pitfall is to assume that any modular kernel is a microkernel. The essential criterion is the amount of service logic that resides in user space versus kernel space, not only the code organisation or build system used by the operating system.

Final Answer:
A microkernel keeps only minimal services like low level address space management, interprocess communication and basic scheduling in kernel mode, while a macro or monolithic kernel keeps many services such as file systems and device drivers inside the kernel.