Introduction to Operating Systems
OPERATING SYSTEMS
What is an Operating System?
From a user-centric perspective, an operating system is a program that acts
as an intermediary between a user and the computer hardware. It defines
an interface for the user to access system services, providing a specific
"view" of the system. This view converts hardware outputs into user-
friendly formats and can hide unnecessary hardware details, even
presenting a different operating environment than what physically exists.
From a system-centric perspective, an operating system efficiently manages
and allocates resources to users. It controls the execution of user programs
and the operations of I/O devices, providing isolation and protection
between different user programs.
Computer System Components
A computer system consists of four main components:
Hardware: Provides basic computing resources like the CPU, memory,
and I/O devices.
Operating System: Controls and coordinates the use of hardware
among various application programs for different users.
Application Programs: Define how system resources are used to solve
computing problems for users, including compilers, databases, and
games.
Users: People, machines, or other computers that interact with the
system.
Types of Systems
Different types of operating systems exist, each designed for specific
purposes:
i. Batch Systems: Process multiple jobs, but only one job resides in memory
and executes to completion before the next one starts. ii. Multi-programmed
Batch Systems: Multiple jobs reside in memory, and the CPU is multiplexed
between them, considering CPU-bound versus I/O-bound jobs. iii. Time-
sharing Systems: Multiple jobs reside in memory and on disk, with the CPU
multiplexed among jobs in memory. Jobs are swapped between disk and
memory, allowing user interaction. iv. Multiprocessing Systems: Utilize
more than one CPU in a single machine to allocate jobs, including
Symmetric Multiprocessing and NUMA machines. Other parallel systems
include multicore processors, distributed systems, and clusters. v. Real-
Time Systems: Designed to run jobs with time guarantees. vi. Other Types:
Include embedded systems and mobile/smartphone operating systems.
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