← Back to SO/1 - OS Intro
  • The OS manages the interaction between users/programs and hardware
  • The OS main clients are programs, that executes billions of instructions

When a program runs:

  • The CPU fetches instructions from memory

  • Decodes and Executes the instructions This is repeated until the program ends

  • The main goal of the OS is to make easy and efficient to run programs by allowing multiple programs to run simultaneously while managing it's IO and memory requests.

Modern OS

  • Abstracts the "low-level" details os hardware through virtualization

  • Provides an Interface (System Call API) for users to tell the OS what to do

  • On top of the OS we can build system programs (GUI, shell, manipulate files/directories, compile/load/execute/debug programs)

  • Ensures performance when running multiple programs accessing shared physical resources

  • Ensures protection by isolating running programs from each other and from the OS

  • Reliability: A failure of the OS makes all applications fail

  • Security: protection against malicious programs

  • Even though there are a limited number os CPU's, users get the idea that several programs are running simultaneously

Mechanisms: how does the OS switch running programs? Policy: which program should be scheduled next?

Memory management: Physical memory can be seen as a simple array of bytes. Programs (running) need to store their instructions and data structures in memory

Persistence: Memory is volatile, meaning that data is lost upon a reboot (or crash) of the computer. Disk devices (e.g., HDDs, SSDs) allow programs to store their data persistently

Running programs → execute instructions (Fetch, Decode, Execute) Virtualization → OS takes physical resources(Memory, CPU, Disk) and transforms it into a general form of itself, sharing resources between programs.

  • The OS is a resource manager, that manages how many programs access the hardware
  • Virtualization of the CPU → Turning a single CPU into the impression that exist an infinity amount of CPU's, allowing many programs to seemingly run at once
  • Concurrency → problems that arise, and must be addressed, when working on many things at once (multi-programming, multi-thread)

OS: -> virtualizes physical resources -> handles through tricky issues related to concurrency -> stores files resistente, making them safe over the long-term