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Operating Systems

What is an Operating System?

-> Software which makes the computer usable

Parts of an Operating System

-> File System

-> Security Manager

-> Communication System

-> Process Manager

-> Memory Manager

-> Graphical User Interface

-> Backup System

-> Web Browser

-> Media Player

-> Compiler

Extreme Approaches: Minimalist Understanding

-> Minimum amount of software required to allow the computer to function

kernel - usually in memory always

process/thread management

communications

memory management

file management

monolithic and micro-kernels

Extreme Approaches: Maximalist Understanding

-> All the software which comes with a standard release of the OS

many utilities and programs

Usable vs. Efficient

-> Some OS designed for specific needs, others are general purpose.

-> A trade off between usability and efficiency

Usable - for whom? -> developer of the system or "ordinary" user

Efficient -> real-time systems, many thousands of transactions a second, battery life

OS Themes

-> Manager Model

collection of managers

prevents improper of devices

each manager is independent

maintains table of information

-> Onion Model

series of layers

outer layers can access resources contained in inner layers but not vice-versa

-> Resource Allocator Model

Related to the manager model

providing the services programs need

must be fair?

-> Dustbin Model

sees the OS as all the bits no one else wants to do

-> Getting Work Done Model

we only use computers to do something else e.g. write an essay, find information etc.

OS has to help us to get our work done

OS Design

-> All in one

all OS components can freely interact with each other

E.g. MS-DOS, Early Unix

MS-DOS

-> written to provide the most functionality in the least space

-> not divided into modules

-> has some structure, its interfaces and levels of functionality are not well separated

Early Unix

-> consists of two separable parts: Systems programs, The kernel

-> provides file system, CPU scheduling, memory management and other operating-system functions

--> Separate Layers - see the Onion Model