Introduction to Operating Systems

Operating System Introduction

• Operating systems manage computer hardware resources
• OSes control and coordinate how hardware is shared among users
• Applications use resources to solve problems
• OSes are essential for user convenience and performance
• Users usually aren't concerned with resource utilization

Computer System Structure

• Four main components: hardware, software, OS, and applications
• Hardware provides basic computing resources (CPU, memory, I/O devices)
• OS manages hardware, controls access, and coordinates use among applications
• Application programs define how system resources are used to solve user problems
• Users include people, machines, and other computers

Operating System Operations

• OSes are interrupt-driven
• Device controllers signal interrupts to OS
• OS handles interrupts by transferring control to the correct interrupt service routine
• Software interrupts (exceptions, traps) occur due to errors or user requests

Computer Startup

• Bootstrap program (firmware) loads at power-up or reboot
• Bootstrap program initializes system aspects
• Operating system kernel loads and begins execution

Interrupt Handling

• OS preserves CPU state (registers, program counter)
• OS determines interrupt type
• Separate code segments handle different interrupt types

I/O Structure

• I/O devices can execute concurrently with CPU
• Device controllers have local buffers for data transfer
• CPU transfers data between memory and device buffers
• Device controllers signal interrupts when I/O operations complete

Storage Structure

• Main memory provides direct CPU access
• Typically volatile (RAM), which is random access memory
• Secondary storage (like hard drives) provides large nonvolatile storage capacity
• Non-volatile memory (NVM) provides faster storage than hard drives with increasing capacity and decreasing prices

Storage Hierarchy

• Storage systems are organized in a hierarchy
• Speed and cost are factors in the hierarchy
• Caching is an important approach to optimize performance by copying data to faster storage

Computer-System Architecture

• Most systems feature a single general-purpose processor
• Multiprocessors systems (parallel systems or tightly coupled systems) are growing
• Increased throughput, economy of scale, and increased reliability are benefits of multiprocessors
• Two types are symmetric (symmetric multiprocessing) and asymmetric (asymmetric multiprocessing)

Dual-Core Design

• Multi-chip and multicore systems contain multiple separate CPUs
• Non-uniform memory access systems are different from regular CPUs
• Clustered systems are multiprocessor systems working together (multiple systems working together)

Computing Environments

• Traditional: Stand-alone general-purpose machines
• Distributed computing: Collection of separate possibly heterogeneous systems networked together. Common communication paths include LANs, WANs, MANs, and PANs
• Client-server: Client requests services from a server.
• Peer-to-peer: Systems are peers that may act as client or server
• Cloud computing: Services (calculations, storage, software) provided across a network

Real-time Embedded Systems

• Real-time embedded systems are prevalent, varied, and often purpose-built
• Time constraints are generally a necessity in this environment

Operating System Operations

• OSes protect themselves and other components through dual-mode operation (user mode and kernel mode)
• CPU mode changes through instructions
• Includes virtual machine manager (VMM) to host guest operating systems
• Bootstrap program loads operating system kernel

Process Management

• A process is a program in execution (active) as opposed to a program (passive)
• Process resources include CPU, memory, and I/O files
• OS manages processes by initialization, termination, and scheduling
• Including process synchronization, process communication, and deadlock handling

Memory Management

• OS manages which parts of memory are in use, how they are used, and moving instructions/data between memory and storage.
• Memory management activities involve keeping track of memory usage, allocating and deallocating, deciding what goes in/out of memory
• Using virtual memory to allow execution of processes that are not completely in memory

File System Management

• OS provides uniform, logical view of information storage abstraction for physical properties.
• OS manages file allocation (on file storage devices) and file access control (which files different users have access to).
• Involves file creation, deletion, directories, mapping, and backup functions

Mass Storage Management

• Data not in main memory or needing long-term storage is stored on mass storage devices like hard drives (HDD)
• OS manages the speed of computer operation through disk subsystem algorithms. This includes mounting, allocating free space, disk scheduling, and partitioning.

Multiprogramming and Multitasking

• Multiprogramming (batch system) improves CPU efficiency by running more than one program at a time so the CPU is always busy
• Time-sharing (multitasking) allows efficient interaction between users and their tasks

Kernel Loads

• System daemons start
• Kernel interrupt-driven (hardware and software)
• Software errors (ex. division by zero), requests, or processes modifying other processes or system are also handled by the kernel.

GNU/Linux and BSD UNIX

• Examples of open-source or free software.
• Available in both source and binary formats.
• Enables studying from the inside out.
• Virtualization allows the use of many operating systems, such as VMware and VirtualBox.

Virtualization

• Emulation used when hardware differs on source and target computers (i.e., PowerPC to Intel x86)
• Interpretation is generally slow
• Often use virtualization to test on different OS systems.
• Several other use cases (like testing apps across different OS versions), for example.