The Role of the Operating System

Abstracts Hardware

Provides a high level of access to the devices in the system

Manages Resources

Fairly (tries to) assigns resources to each task

Privileged/Kernel vs User Mode

  • Programs run in user mode

  • OS runs in kernel mode

  • Programs in user mode can't do all instructions; goes through the kernel to request access

    • Disabling interrupts
    • Low level hardware access

Kernel-only Access

  • Disabling interrupts
  • Setting time of day clock (..ehhhh.)
  • Change the memory map (Allocated RAM to the process and other processes)
  • Hard-disk controller register

User can perform reading the time of day clock, fsync

File Descriptors

0 - stdin 1 - stdout 2 - stderr

Threads vs Process

Threads are like forks, except that they share their global memory.
Local memory is however independent.