Introduction to Operating Systems

Introduction to Operating Systems

1. Definition

   • The OS makes the hardware usable
   • It is a program e.g. Linux, MacOS, FreeBSD

2. Types of OS

   • Single User Systems: may provide just one virtual machine for one user but some provide more than one VM
   • Embedded Systems: used to control particular process/piece of equip, e.g. mobile phone, washing machine, trains, TV
   • General Purpose Systems: used for many diff tasks at diff levels of complexity, often multi-user (can be used by more than 1 person at the same time, implying security issues e.g. Unix on the PC: Linux

3. Operating System Structure

   • Monolithic
     • One large program; difficult to maintain and enhance; not considered further
   • Layered
     • System should have logically distinct components, each handling an aspect of the system's requirements
     • Divided in modules in layers; more theoretical than practical
     • Structure resembles an onion, each layer represents a set of functions dependent only on inner layers
   • Client Server (not microkernal)
     • Modules have equal status and communicate by sending messages

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