Intro to OS & Kernel Architecture

An Operating System (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. It acts as an intermediary between the user of a computer and the computer hardware.

1. Primary Goals of an OS

1. Convenience: Makes the computer system convenient and easy to use for the user.
2. Efficiency: Allows the computer hardware resources to be used in an efficient manner.
3. Ability to Evolve: Should be constructed in such a way as to permit the effective development, testing, and introduction of new system functions without interfering with service.

2. Core Functions

• Process Management: Creating, scheduling, and terminating processes.
• Memory Management: Allocating and deallocating memory space to programs in need of these resources.
• File Management: Managing files, directories, access control, and storage.
• Device Management: Keeping track of all devices. This module is typically called the I/O controller.
• Security: Protecting data and information from unauthorized access.

3. Types of Operating Systems

• Batch OS: Users do not interact with the computer directly. Each user prepares their job on an off-line device like punch cards and submits it to the computer operator.
• Time-Sharing (Multitasking) OS: Enables many people, located at various terminals, to use a particular computer system at the same time.
• Distributed OS: Uses multiple central processors to serve multiple real-time applications and multiple users.
• Real-Time OS (RTOS): Used when rigid time requirements have been placed on the operation of a processor or the flow of data (e.g., medical imaging systems, industrial control systems).

4. The Kernel

The Kernel is the central component of an operating system. It is the core program that manages the system's resources and the communication between hardware and software components. It is one of the first programs loaded on startup (after the bootloader).

Kernel Architectures:

• Monolithic Kernel: All OS services run along with the main kernel thread, thus residing in the same memory area. This provides rich and powerful hardware access (e.g., Linux).
• Microkernel: User services and kernel services are kept in separate address spaces. This makes the OS more stable and secure but introduces overhead due to message passing between spaces (e.g., QNX, Minix).