Operating System Boot Process

This is just a basic description of how a Pentium computer boots.

  • First the BIOS is loaded from motherboard RAM.
    • BIOS checks how much RAM is installed.
    • Other devices like keyboard / mouse are checked.
    • Then checks ISA and PCI busses.
  • BIOS then determines the boot device listed in CMOS memory.
    • Usually floppy -> CD -> HDD
  • The first sector of boot device is read and loaded
    • Examines the partition table at end of the boot sector, to determine which partition to use.
  • The boot loader is read from that partition.
    • Boot loader loads the OS

Major OS Types

Mainframe OS

Heavily oriented towards processing many jobs at once. However nowdays it is being slowly replaced by UNIX.

Server OS

They run on servers, usually very large PCs or even mainframes. They serve multiple users at once.

Common server OSes: Solaris, FreeBSD, Linux and Windows Server.

Multiprocessor OS

Nowdays most OSes are multiprocessor, for example Windows and Linux. Since most PCs have multiple cores, or even multiple CPUs.

Personal Computer OS

This is widely known, for example macOS, Windows and Linux. They usually support multiprogramming, and aims to provide the best experience for a single user.

Handheld OS

Old school Symbian OS and Palm OS, nowdays it is Android, which is Linux, and iOS, which is UNIX.

Embedded OS

Major difference between embedded OS and others is: It does not need to run untrusted software. That leads to simplifications. For example, a MP3 player.

Sensor Node OS

TinyOS is one of the wellknown ones. These OS are found on sensors, which usually wirelessly communicate with eachother and protect building parameters.

Real-Time OS

These are used in assembly lines. Time is critical, for hard real-time systems, deadlines must be met. Soft real-time systems can miss some deadlines.

Because time is critical, usually there is no protection.

Smart Card OS

The smallest you can get is smart card OSes. Sometimes smart card OSes runs JVM (Java). They are usually powered by the machine they are in contact with.

What is an OS

Operating System
  • Provides services
  • Resource manager
  • Control program (protection)


A process contains

  • An address space
  • Set of OS resources
  • Set of general-purpose registers with current values

What is a Context Switch