OS MODULE1

Operating System

is a system software that manages computer hardware and software resources and acts as an intermediary between users and hardware which provides services to applications

Operating System

Its purpose is to execute user programs and make solving user problems easier, while ensuring efficient use of hardware resources

Kernel

The one program running at all times

System Programs

Utilities that provide a convenient environment (compilers, shells, file, tools).

Application Programs

User defined tasks such as browsers, word processor, games.

User View and System View

What are the two views of the operating system?

Hardware

Provides basic computing resources

Operating System

Controls and coordinates use of hardware among users and applications

Application Programs

Define how system resources solve user tasks.

Users

People or other systems interacting with the computer

Interrupt

Is a signal that alerts the CPU to an event requiring attention

Maskable interrupts

can be delayed by disabling them; non - maskable cannot

Hardware interrupts and Software interrupts

Types of interrupts

Bootstrap Program

When the computer powers on, the CPU executes this program which is stored in ROM/firmware.

ROM/Firmware

Where is the bootstrap program located?

BIOS/UEFI

are responsible for hardware initialization and firmware-to-OS hand-off.

Registers

Fastest storage type?

Cache

Very fast but not the fastest storage type

Main memory

Fast storage type, not very fast and not the fastest

Secondary storage (SDD, HDD)

This type of storage has moderate speed.

Von Neumann Architecture

is the fundamental design model for most modern computers. Its defining characteristic is stored-program concept, which means programs (instructions) and data share the same main memory space. This simple structure allows for flexibility but creates a '“bottleneck” where the CPU is often waiting on data transfer to/from memory.

The Instruction Cycle

is the continous, repetitive three-step process that the CPU performs to execute all the instructions that make up a program. It is the engine of the computer’s operation

Fetch

The CPU retrieves (fetches) the next instruction from memory, based on the address in the Program Counter (PC)

Decode

The CPU determines what operations the instruction specifies (e.g., add, jump) and identifies the data (operands) needed.

Execute

The CPU performs the required operation, such as calculating a value or moving data

DMA

Because I/O devices are slow compared to the CPU, the system uses ___ to transfer blocks of data without constant CPU intervention

DMA Controller

Transfers data directly between I/O device and memory

Computer - System Architecture

Defines how CPU, memory, and I/O devices interconnect and share resources.

Sing-Processor System

One CPU executes instructions sequentially. Simple to manage but lacks parallelism

Multiprocessor Systems

Two or more processors share a common memory and communication bus

Asymmetric Multiprocessing (AMP)

Master-slave arrangement; one CPU controls others

Symmetric Multiprocessing (SMP)

All processors are peers and execute the same OS.

NUMA

This system divides memory into local and remote regions

local memory

Each processors acesses its _____ ______ faster than remote memory on another prcoessor

NUMA-aware

OS and applications must be __________ to place data near executing CPU

blade server

is a modular computing system where multiple thin server boards share a single chassis for power, cooling, and network connections.

Clustered System

consists of multiple independent computers (nodes) working together and connected by a high - speed network.

Asymmetric Clustering

One node standby, others active

Symmetric Clustering

All nodes active and share load

Fault tolerance

service continues even if one node fails

Load balancing

Distributes requests dynamically

Scalability

Add or remove nodes without down time

Improved performance

parallel executing can ______ ______

Operating System

acts as both resource allocator and control program managing hardware operations

Multiprogramming

Keeps the CPU busy by organizing jobs so that CPU always has one to execute

Multitasking (Time-sharing)

CPU Switches rapidly among users for interactive operation

Figure

Memory layout for a multiprogramming system

User Mode

Executes application programs with limited privileges

Kernel Mode

Executes OS code with full hardware access

TImer

Prevents a program from monopolizing the CPU

Timer

Used by scheduler to regain control after time slice expires.

Process Management

Handles creation, scheduling, and termination of proceses

File - System Management

Provides logical organization and access to data

Memory Management

Allocates sand tracks main memory usage

File-System Managemet

Provides logical organization and access to data

Mass-Storage Management

Manages secondary storage and disk scheduling

Cache Management

Improves performance by using fast temporary storage

I/O System management

Coordinates communication between devices and the CPU

Protection

Provides controlled access to system resources such as files, memory, and devices.

Security

Defends the system against internal and external threats

Authentication

Verifies user identity

Authorization

Determines user privileges

Encryption

Protects data confidentiality

Auditing

Tracks and logs user actions

Virtualization

Allows multiple logical instances of hardware or operating systems to share a single physical machine

Virtual Machine Monitor

Manages an allocates resources among virtual machines

Hardware Virtualization

Runs several OS instances (e.g., VMware, Hyper-V)

OS-Level Virtualization

Multiple isolated containers (e.g., Docker)

Distributed System

A collection of physically separate computers that cooperate to provide unified services

Traditional Computing

Standalone desktop or mainframe systems with direct user interaction

Mobile Computing

Portable devices using touch input and wireless conectivity

Client- Server Computing

Client request resources or services from centralized servers

Peer-to-Peer Computing

Each node acts as both client and server

Cloud Computing

On-Demand network access to shared computing resources

Real-Time and Embedded Systems

Special-purpose systems with strict timing constraints

Free and Open-Source Operating Systems

Originated from the early UNIX systems developed at AT&T Bell Labs in the 1970s

Free Operating Systems

Free and Open-source operating systems (FOSS) allow users to access, modify, and distribute the source code

GNU/Linux

Initiated b Linus Torvalds (1991) to create a free UNIX-like kernel. Used extensively in servers, desktops, and embedded systems

BSD Linux

Developed at the University of California, Berkeley. Known for stability, performance, and strong networking stack

Solaris

Originated from Sun Microsystems; now open-sourced as OpenSolaris. Designed for scalability and large systems with the ZFS file system and Dtrace monitoring

Operating System

is the core software that manages hardware and provides services to applications