Introduction to Operating Systems

Operating System Introduction

• An operating system acts as an intermediary between the user and computer hardware.
• Operating systems aim to execute user programs, solve user problems, enhance usability, and efficiently use computer hardware.
• Computer systems consist of hardware, operating systems, application programs, and users.
• Different types of systems cater to various users and devices (e.g., shared, handheld, dedicated, embedded).

Operating System Components and Functions

• Interrupts: Transfer control to interrupt service routines via interrupt vectors. Interrupt architecture saves interrupted instruction addresses.
• Traps/Exceptions: Software-generated interrupts, either errors or user requests.
• Interrupt-driven OS: Responds to events via interrupts, typically through polling or vectored interrupt systems.
• Device Status Table: Contains info about 1/0 devices (type, address, status)
• System Calls: User requests to the OS for 1/0 completion.
• Kernel: A core part of the OS, running continuously, distinct from other system or application programs.
• Bootstrap: A ROM-resident program that initializes the system and loads the OS.

Computer System Operation

• Concurrent Operations: CPU and 1/0 devices execute concurrently. Data transfer involves local buffers.

• Storage Hierarchy: Organized by speed, cost, and volatility (registers, cache, main memory, SSD, hard disk, optical disk, magnetic tape).

  • Caching copies information from slower to faster storage for performance.
  • If information is found in cache, it's utilized directly. Otherwise, it's loaded from the slower storage.

Time Sharing (Multitasking)

• Time-sharing (Multitasking): Allows multiple users to interact with jobs seemingly simultaneously.
• Multiprogramming (Batch): Primarily used for efficiency.
• Multitasking goals: short response times, interaction, memory and CPU/I/O utilization.
• Scheduling: Process selection for CPU execution
• Swapping/Virtual Memory: Allows running processes not fully in memory.

Multiprocessor Systems

• Asymmetric Multiprocessing: Each processor performs specific tasks.
• Symmetric Multiprocessing: All processors perform all tasks.
• Advantages: Increased throughput, economy of scale, increased reliability (fault tolerance).

Dual-Mode Operation

• Allows OS protection of itself and system components by designating privileged instructions.
• The mode bit distinguishes between user and kernel mode.
• System calls change mode to kernel and restore it to user.

Process Management

• Process: A program in execution; it's active, instead of passive like a program.
• Requirements: CPU, memory, 1/0, files, initialization data.
• Termination: Reclaims resources.
• A multitasking environment must manage the values of processes.

Memory Management

• Memory management: Tracks what's in memory and which processes use it.
• Activities: Optimizing CPU utilization and response time, allocating/deallocating memory, swapping processes in/out.

Storage Management

• Role: Provides a uniform logical view of storage devices (disks, tapes) hiding physical properties.
• Properties: Access speed, capacity, data transfer rate, access method
• Activities: Free space management, storage allocation, disk scheduling.

I/O Subsystem

• Role: Hides device peculiarities, provides general drivers and specific drivers.
• Memory Management of I/O: Includes buffering, caching, spooling.
• Buffering: Temporarily stores data during transfer.
• Caching: Stores parts of data in faster storage.
• Spooling: Overlaps output with input of other jobs.

Protection and Security

• Protection: Controlling process/user access to resources.
• Security: Protecting against internal/external threats.
• Threats: Denial of service, worms, viruses, identity theft, theft of service.
• Distinguishing users and granting access via user IDs (security ID), group ID.
• Privilege escalation: Access with more rights.

Computing Environments

• Traditional Computing: Stand-alone general-purpose machine.
• Mobile Computing: Handheld smartphones, tablets.
• Distributed Computing: Networked systems, client-server systems/computing.
• Client-server: Client requests, server provides services; file servers, compute servers.

Open Source Operating Systems

• Open source OS's are available with source code, unlike closed source (binary format).
• Open source movement began with the Free Software Foundation and the GNU General Public License (GPL).
• Examples: GNU/Linux, BSD UNIX.