Operating Systems Quiz

Introduction to Operating Systems

• Operating systems act as intermediaries between users and computer hardware
• Fundamental goals: execute user programs efficiently, make the system user-friendly, and use hardware resources efficiently
• Computer systems comprise hardware (CPU, memory, I/O devices), operating system, application programs, and users (people, machines, other computers)

Computer System Structure

• Hardware provides basic computing resources
• Operating systems control and coordinate the use of hardware among various applications and users
• Application programs define how system resources are used to solve user computing problems
• Examples of application programs: word processors, compilers, web browsers, database systems, video games

Objectives

• Describe the basic organization of computer systems
• Explain the major components of operating systems
• Provide an overview of different computing environments
• Explore various open-source operating systems

What is an Operating System?

• A program that acts as an intermediary between a user of a computer system and the computer hardware
• Its goals include executing user programs, simplifying user problem-solving, and managing computer hardware efficiently

Computer-System Operation

• Multiple CPUs and device controllers can execute concurrently
• Each device controller has a local buffer
• CPU moves data between main memory and local buffers
• Device controllers inform the CPU when operations are completed via interrupts, which are software-generated interruptions

Common Functions of Interrupts

• Interrupts transfer control to the interrupt service routine (ISR), generally via the interrupt vector
• Interrupt architecture saves the address of the interrupted instruction
• A trap/exception is a software-generated interrupt, often caused by errors or user requests
• Operating systems typically are interrupt-driven

Interrupt Handling

• The operating system preserves the CPU's state (registers and program counter) upon an interrupt
• It determines the type of interrupt and executes the appropriate code to handle it
• Different interrupts can be handled by different pieces of code (polling or vectored interrupt systems)

I/O Structure

• After I/O operation begins, the operating system returns control to the user program typically not waiting for completion
• It uses wait instructions and/or wait loops (potentially contention issues) to pause operation until the next interrupt
• System calls allow user programs to request I/O operations.
• The device-status table maintains the state of each I/O device
• The operating system determines the status of I/O devices and adjusts the table entries to include an interrupt

Direct Memory Access (DMA)

• Used for high-speed I/O devices that transfer data at speeds near main memory rates
• Device controllers transfer data directly to main memory without CPU intervention
• Fewer interrupts are generated per block instead of per byte

Computer System Organization

• One/more CPUs, device controllers connect through a common bus
• Shared memory access among components and CPUs
• Concurrent execution of CPUs and devices with potential competition for memory cycles

Computer-System Architecture

• Commonly uses a single, general-purpose processor
• Multiprocessor systems (parallel or tightly-coupled) are also prevalent
• Advantages include increased throughput, economy of scale, and enhanced reliability (graceful degradation or fault tolerance)
• Two key types are Asymmetric and Symmetric Multiprocessing

Symmetric Multiprocessing (SMP)

• Each processor can perform all tasks
• Centralized memory access and communication between CPUs

Multi-chip and Multicore

• More than one chip, CPU core, or processors

Clustered Systems

• Multiple systems working together through a storage-area network
• Provides high availability services that are resilient to failures
• Types include asymmetric clustering (one machine in standby mode and detecting failures), symmetric clustering (multiple nodes running applications and monitoring each other)

Operating System Structure

• Multiprogramming (Batch systems): A subset of jobs loaded in memory, and the operating system allocates execution time among them.
• Timesharing (multitasking): Frequently switching between jobs to allow users to interact with each job while it's running, creating interactive computing experience.
  • Response time is kept under 1 second.

Memory Management

• To execute, a program needs parts of its instructions and data present in memory.
• Memory management determines which parts of memory are in use and who is using them.
• It's responsible for optimizing CPU utilization and the computer's response to users.
• This includes keeping track of which processes and parts of processes are in memory, deciding what to move in and out, and allocating and deallocating memory space.

Storage Management

• The operating system provides a unified, logical block to represent different information storage types (abstracting underlying physical properties).
• Different storage devices (disk drives, tape drives) have varied properties (speed, capacity, transfer rates, access methods).
• File management includes organization into directories and includes access control.
• OS activities for managing information storage include creating and deleting files, manipulating files and directories, backing up files, and mapping files into storage media.

Mass-Storage Management

• Typically, disks are used for storing data not currently required in main memory; this may be kept for extended time periods.
• This process requires careful management
• Crucial for maintaining the speed of computer operation.
• Related OS activities include free space management, storage allocation, disk scheduling, and managing tertiary storage.

Cache

• Information is repeatedly copied from slower to faster storage systems to improve processing speed.
• Main memory acts as a cache for secondary storage.
• Cache management is important because sizes are smaller than storage.
• Issues include replacement policy and management of the cache size..

I/O Subsystem

• One goal of operating systems is to hide the specifics of how hardware devices work.
• The I/O subsystem controls devices using memory management, buffering, caching, and spooling.
• Drivers are programmed separately to provide access to specific hardware devices.

Protection and Security

• Protection mechanisms control access to system resources.
• Security systems defend the system against internal and external threats (e.g., denial-of-service attacks, viruses, identity theft, theft of service).
• Typically, user IDs and group IDs are used to differentiate among users and determine access rights.
• Operations like privilege escalation allow authorized users to alter their effective access rights.

Kernel Data Structures

• Kernel data structures typically resemble common programming concepts (e.g., singly linked list, doubly linked list, circular linked list).
• Data structures useful for organizing and managing information.

Computing Environments

• Different Computing Environments:
  • Traditional: Standalone general-purpose machines are common, but systems often connect to each other, including through the internet and using portals, or network computers (web terminals) or mobile devices connected by wireless networks.
  • Mobile: Smartphones, tablets, etc. have additional characteristics (e.g., GPS, gyroscope) compared to traditional laptops and employ augmented reality apps; wireless or cellular data networks provide connectivity.
  • Distributed: Networks of separate, potentially heterogeneous systems are linked together to form networked environments.
  • Client-Server: Dumb terminals have been replaced by smart personal computers, and servers manage client requests across a network.
  • Peer to Peer: Distributed systems where no single machine is designated as a client or server.
  • Virtualization: Allows running multiple operating systems on a single computer; emulation and interpretation are employed, using a virtual machine manager.
  • Cloud: Computing, storage, and apps are delivered as a service on the network. Logical extension of virtualization. Types of cloud services: public cloud, private cloud, hybrid cloud. Services like SaaS, PaaS, IaaS (Software as a Service, Platform as a Service, Infrastructure as a Service).
  • Real-time embedded systems: Widely prevalent form of computers with considerable variations. Special purpose OS for these systems. Some have no OS. Processing must occur within fixed time constraints

Open-Source Operating Systems

• Open-source operating systems, like GNU/Linux and BSD UNIX, are freely available, permitting source code modification; they oppose copy protection and Digital Rights Management.
• Typically distributed under license by the Free Software Foundation with "copyleft" license terms