Operating System Definition

• Resource allocator
  • Manages all resources
  • Decides between conflicting requests for efficient and fair resource use
• Control program
  • Controls execution of programs to prevent errors and improper use of the computer

Operating System Composition

• User
  • People, machines, other computers
• Application programs
  • Define the ways in which the system resources are used to solve the computing problems of the users
  • Word processors, compilers, web browsers, database systems, video games
• Operating System
  • Controls and coordinates use of hardware among various applications and users
  • Windows, Linux, macOS
• Hardware
  • Provides basic computing resources
  • CPU, memory, I/O devices

Operating System functionality

• Operating system is a software layer between the hardware and the application programs/users which provides a virtual machine interface: easy and safe.

• The one program running at all times on the computer is the kernel, everything else are:
  • a system program (ships with the operating system)
  • an application program

Computer System Organization

Storage Structure

• Register
  • A very small, high-speed memory inside the CPU.
  • Stores instructions, operands, and execution results.
• Cache (L1, L2, L3)
  • Faster than RAM, used to reduce access time to main memory.
  • L1 is the smallest but fastest, while L2 and L3 are larger but slower.