Summary

• Components of a modern computer system

  • 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


  1. Busy waiting

  2. Interrupt processing

  3. Direct Memory Access (DMA)
• 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 termination


  Normal and error exits, fatal errors, and being killed by another process
• Process types


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


  • Running
  • Ready
  • Blocked
• 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


  Supports parallelism and shared address space, with lower overhead than creating a process
• 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, with the calling thread usually receiving an identifier for the new thread
• Thread termination


  Analogous to process termination, with some systems allowing threads to wait for others to finish in a "join" operation
• POSIX Threads (Pthreads)


  A standard API for thread management, implemented by most POSIX OSes
• User-level threads


  Allow for customization of scheduling algorithms and can be implemented on OSes with no thread support, making context switching simple and fast
• User-level threads disadvantages


  Blocking system calls affect all threads in a process, relying on voluntary CPU relinquishment
• Kernel-level threads


  Offer advantages such as transparent use of blocking system calls, no need for new nonblocking system calls, and page faults caused by one thread not affecting others
• Interprocess communication (IPC)


  Processes in multiprocess systems need to communicate to pass relevant information, prevent simultaneous access to exclusive resources, and work with appropriate sequencing of events
• Race conditions


  Occur when multiple processes access shared data simultaneously, leading to unpredictable results
• Mutual exclusion


  A technique used to avoid race conditions by ensuring that processes accessing shared resources do not overlap in their critical regions
• Good solution to race conditions

  • Ensures no two processes are simultaneously inside their critical regions, prevents processes running outside their critical regions from blocking others, and ensures no process waits indefinitely to enter its critical region