CS2850 Operating Systems

• Components of a Modern Computer

  • Processors
  • Main memory
  • Disks
  • Printers
  • Keyboard
  • Mouse
  • Display
  • Network interfaces
• Hardware


  The physical components of a computer system
• Software


  The logical applications that run on the hardware
• Operating system


  A layer between end user applications and the hardware, allowing applications to be developed without having to be aware of all hardware specifics
• Operating system


  • Transforms primitive and awkward hardware architecture into beautiful abstractions
  • Provides abstractions to application programs and manages complex systems while allocating resources in an orderly and controlled manner
• The evolution of computer technology can be categorized into five generations, starting from vacuum tubes to mobile computers
• Central Processing Unit (CPU)


  A key component of modern computers, responsible for executing instructions and storing temporary values
• CPU performance improvements


  • Techniques like pipelining, multithreading, and multicore processors
  • Specialized processors like Graphics Processing Units (GPUs) have also contributed to the advancement of parallel computations
• Memory hierarchy


  • L1 cache
  • L2 cache
  • Main memory (RAM)
  • ROM
  • Flash memory
• Magnetic disks (HDDs)


  Cheaper and have more capacity than RAM, but slower
• Solid State Drives (SSDs)

  Faster and use flash memory, but more expensive
• Hybrid drives


  Combine SSDs and HDDs for high-speed access without compromising capacity
• Virtual memory


  A solution for programs that don't fit in existing memory, using disk space to temporarily store information
• I/O device


  Consists of a controller and the device itself, with the controller accepting commands from the operating system
• Device drivers


  Used to minimize operating system complexity and created by vendors for each supported operating system
• I/O methods


  • Busy waiting
  • Interrupt processing
  • Direct Memory Access (DMA)
• Interrupt processing involves running the interrupt handler and returning to the user program
• DMA allows for minimal CPU intervention by using a chip to transfer data between devices and memory
• Types of operating systems

  • Mainframe
  • Server
  • Multiprocessor
  • Personal computer
  • Handheld computer
  • Embedded
  • Sensor node
  • Real-time
  • Smart card
• Process


  A program in execution, associated with an address space and a set of resources
• Process A creates two child processes, B and C, while Process B creates three child processes, D, E, and F
• Process information


  • Process ID
  • Name
  • User
  • Executable file
  • Register values
• Pseudo-parallelism


  In multiprogramming systems, CPUs quickly switch from process to process, giving the illusion of parallelism even with just one CPU
• Process creation


  1. System initialization

  2. Process creation system call

  3. User request

  4. Initiation of a batch job
• Process creation in POSIX OSes

  New process is created using the fork system call, which creates a clone of the calling process
• Process creation in Windows

  Process creation is done in one step using the CreateProcess call
• The address spaces of parent and child processes are separate in both POSIX and Windows
• Conditions for process termination

  • Normal exit
  • Error exit
  • Fatal errors
  • Killed by another process
• Process types


  • Interactive processes (file explorer, web browser)
  • Daemons (work in the background and react to specific occurrences)
• Process states


  • Running
  • Ready
  • Blocked
• Running


  The process is actively using the CPU
• Ready


  The process is temporarily stopped to allow another process to run
• Blocked


  The process is unable to run until an external event occurs
• Process table entry


  Includes various fields that provide information about a process
• CPU utilization


  Can be approximated as 1 minus the product of the probability of a process waiting for I/O and the number of processes in memory
• Thread


  Multiprogramming supports process management, while parallelism and shared address space benefit from threads
• Threads


  • Creating a thread has significantly lower overhead than creating a process, and context switching between threads is faster
  • Sharing address space facilitates writing code for multiple activities that can block and interact
• Multithreading examples


  • Word processor with three threads
  • Multithreaded Web server with dispatcher and worker threads
• Thread states


  • Running
  • Ready
  • Blocked
• Thread creation


  A single thread is present which can create new threads, and the calling thread usually receives an identifier for the new thread