Operating Systems Overview Quiz

Introduction to Operating Systems

• Operating systems are programs acting as intermediaries between users and computer hardware
• Operating systems manage and control hardware resources
• Key goals include executing user programs, making use of hardware efficiently, and improving user experience
• Computer systems are composed of hardware, operating systems, application programs, and users

Computer System Structure

• A computer system is divided into four main components:
  • Hardware: Provides basic computing resources (CPU, memory, I/O devices)
  • Operating system: Controls and coordinates the use of hardware among various applications and users
  • Application programs: Define how system resources are used to solve computing problems
  • Users: People, machines, or other computers interact with the system

What Operating Systems Do

• Operating systems manage resources, handle user requests
• User convenience prioritized in some systems
• Resource utilization prioritized in others, especially for shared computers
• Handheld devices prioritize usability and battery life
• Some embedded computers lack a user interface

Operating System Definition

• An operating system is a resource allocator
  • Manages all resources and decides how to allocate them
  • Acts on competing user requests efficiently and fairly
• An operating system is a control program
  • Controls the execution of programs to prevent errors and misuse of the system

Operating System Definition (continued)

• No single, universally accepted definition
• A good approximation is everything a vendor supplies with an OS
• The kernel is the one program running continuously in the computer, and everything else is either a system program or an application program

Computer Startup

• The bootstrap program, typically stored in ROM or firmware, initializes system components and loads the operating system kernel
• The kernel takes control and starts the operating system execution

Computer System Organization

• Multiple CPUs and devices interact through a common bus that shares memory
• Concurrent execution occurs as CPUs and devices compete for memory cycles

Computer-System Operation

• I/O devices and CPUs can run concurrently and operate independently
• Device controllers manage specific device types and have local buffers to communicate data to and from general-purpose CPUs

Common Functions of Interrupts

• Interrupts transfer control to interrupt service routines via an interrupt vector
• Interrupt architecture saves the address of the interrupted instruction
• Traps or exceptions are software-generated interrupts, triggered by errors or user requests
• Operating systems are interrupt-driven

Interrupt Handling

• The operating system saves the CPU state, including registers and the program counter, when an interrupt occurs
• Determines the interrupt type using polling or a vectored interrupt system
• Separate code segments handle different interrupt types

Interrupt Timeline

• The timeline shows how the CPU and I/O devices operate concurrently
• The system switches between user processes, I/O interrupts, I/O processing, and I/O device activity

I/O Structure

• After an I/O operation starts, the operating system returns to the user program only upon completion
• The wait instruction idles the CPU until the next interrupt
• At most one outstanding I/O request occurs at any given time
• The system call requests the operating system to allow the user to wait until I/O is complete
• Device-status tables help track I/O device status

Storage Definitions and Notation Review

• The basic unit of storage is the bit
• A byte (8 bits) is the most common chunk of storage in most computers
• A word is the native unit of data in a given computer architecture
• Computer storage is generally measured in bytes and collections of bytes

Storage Structure

• Main memory is accessible by the CPU directly for random access
• Main memory is volatile storage
• Secondary storage is a non-volatile extension of main memory, providing large storage capacity
• Hard disks use magnetic recording material on platters divided into tracks and sectors
• Solid-state drives are faster than HDDs and non-volatile

Storage-Device Hierarchy

• Storage systems are organized into a hierarchy based on speed, cost, and volatility
• Caching temporarily copies information into faster storage media

Caching

• A crucial principle in computer systems, performed at various levels (hardware, operating system, software)
• Copied information from slower storage temporarily to faster storage
• Faster storage (cache) is checked first if information exists
• Data is used directly from cache if it exists, otherwise moved to cache and used there
• Cache is smaller than the storage being cached

Direct Memory Access Structure

• DMA allows high-speed I/O devices to transmit data directly to memory
• Device controllers transfer data blocks from buffer storage directly to memory without CPU intervention, generating just one interrupt per block instead of per byte

Computer-System Architecture

• Most systems use a single general-purpose processor, but special-purpose processors exist
• Multiprocessors, also known as parallel or tightly-coupled systems, offer advantages including increased throughput, economy of scale, and increased reliability

Symmetric Multiprocessing Architecture

• A diagram of symmetric multiprocessing where multiple CPUs share memory
• Each CPU has its own registers and cache

A Dual-Core Design

• Multi-chip or multicore systems with multiple separate CPU systems on a single chassis

Clustered Systems

• Multiple systems working together (like multiprocessors), often sharing storage via a SAN
• Provides fault tolerance and high availability
• Asymmetric clustering has one machine in hot-standby mode and can switch to it on failure
• Symmetric clustering has multiple processors running and monitoring one another
• High-performance or HPC clusters are especially geared towards parallelization

Operating System Structure

• Multiprogramming (batch systems) keep the CPU and I/O devices busy by organizing jobs
• Timesharing (multitasking) switches between jobs to provide interactive computing
• Different processes may use memory concurrently

Memory Layout for Multiprogrammed Systems

• A diagram showing the operating system and multiple jobs in memory

Operating-System Operations

• Operating systems are interrupt-driven, handling hardware and software interrupts
• Software interrupts include software errors, requests for OS services, or other processes interfering with the OS

Operating-System Operations (continued)

• Dual-mode operations (user mode and kernel mode) allow an operating system to protect itself and other system components
• Mode bits distinguish running user or kernel code, designating some instructions as privileged

Transition from User to Kernel Mode

• Timers prevent infinite loops by interrupting the CPU after a set time
• A counter decremented by the physical clock is controlled by the OS
• When counter reaches zero, an interrupt is generated

Process Management

• A process is a program in execution and the key for any operating system
• Processes need resources like CPU, memory, I/O, and files for completion
• Single-threaded processes have one program counter
• Multi-threaded processes have one program counter per thread
• Typically a system has several user and operating system processes executing concurrently
• Concurrent operation is accomplished through CPU multiplexing

Process Management Activities

• OS responsibilities include creating and deleting processes, suspending/resuming them, handling synchronization, communication, and deadlock

Memory Management

• Memory management executes programs, keeping track of which sections are used and by whom, deciding what to move in, and out of memory, and allocating/deallocating memory
• The goal is optimizing CPU usage and user response time

Storage Management

• OS provides a uniform logical view of storage, abstracting physical properties into logical storage units (files)
• Each storage medium (e.g., disk drives or tapes) is controlled by a device, with properties like access speed, capacity, and access methods (sequential or random)
• File management involves organizing files into directories and controlling access to those files

Mass-Storage Management

• Disks store data that doesn't fit in main memory or data needing long-term storage
• Proper management is crucial to computer performance
• OS activities include free space management, storage allocation, and disk scheduling

Migration of data "A" from Disk to Register

• Multitasking environments must access the most recent value of data regardless of its location

I/O Subsystem

• A key OS purpose is hiding hardware device peculiarities from users
• I/O subsystem manages I/O resources, performing tasks such as buffering, caching, spooling

Protection and Security

• Protection mechanisms control access to resources by processes or users
• Security mitigates internal and external threats

Computing Environments

• Traditional systems (standalone machines) differ from mobile systems (phone, tablets)
• Distributed computing uses networked heterogeneous systems working together to provide services
• Examples include client-server, file-server systems, peer-to-peer, and others

Open-Source Operating Systems

• Available in source code format
• Opposed to copy protection and DRM
• Started by the Free Software Foundation (FSF)
• Use the GNU Public License (GPL)
• Includes GNU/Linux, BSD UNIX, parts of Mac OS X, and more