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What is an Operating System?
- This is a collection of software that
- managers computer hardware resources and provides common services for computer
- *Time sharing Oss schedule tasks for
- efficient use of the system, allocation of processor time, mass storage etc*
- *Acts as intermediary between hardware and
Types of OSs
- Multi tasking Os that aims to execute
- real-time apps, using specialised scheduling algorithms so that they can
- achieve a deterministic nature of behaviour.
- *They have an event driven or time sharing
Objectives of real time OSs
Quick and predictable response to events.
What is event driven design?
- Switches between tasks based on their
- priority or external events
What is time sharing design?
Switches tasks based on clock interrupts.
- Allows multiple users to log on
Examples of Multi-User OS
Time sharing systems
Multi Task OS
- Allows more than one program to run at a
Examples of Multi-tasking OS
Windows OS, MAC OSX, Linux
Types of multi-tasking
How pre-emptive types of OS work
- OS slices CPU time and allocates one slot
- to each program.
How cooperative types of OS work
- Processes give time to other processes in
- determine manner.
Manages a group of independent unified computer
- Designed to be used in embedded computer
- *operate in small machine like PDAs, work
- with minimal resource. E.g. Windows CE and Minix 3*
Examples of OSs
MAC OS X
What is Kernel?
- Hub of an OS that acts as a bridge between
- application and actual data processing at the hardware level.
How the Kernel works
- Allocates time and memory to programs,
- handles file storage and communication in response to system calls.
- It enables programs to execute, handles
- events generated by system (software) calls and interrupts (Hardware). It also
- manages access to resources.
System calls are initiated by?
- User level programs, like opening files and
- starting programs.
What is shell?
- Software that provides and interface for
- users of an OS to access the services of the kernel.
How the shell works
Acts as interface between user and kernel
It’s a CLI
- Interprets commands and arranges for their
- carrying out
- Allows programs to be started and give them
- session specific arguments
- Allows trivial operations on local storage
- like listing directory contents, moving and copying file across the system.
Functions of OSs
File system management
- Provides convenient environment for the
- user to execute programs, without worrying about complex tasks like allocating
- and de-allocating memory.
- Carries out underlying I/O operations on
- behalf of the user
File system management
- Frees the user from complex tasks by
- manipulating files in I/O operations and managing secondary storage.
- Exchanging information between processes on
- different computer systems
- Frees the user from worrying about system
- errors propagating and causing system malfunctions by monitoring the system for
Main/primary memory management
I/O system management
Process management (Components of OS)
Manages multiple user and system process. E.g. printer spooler, name servers, files servers etc
What is a process?
One instant of a program in execution
What does a process consist of?
- Includes the complete execution context
- (Code, data, PC registers, OS resources in use)
Five major activities of OS in process management
- Creation and deletion of system and user
Suspension and resumption of processes
A mechanism for process synchronisation
A mechanism for process communication
A mechanism for deadlock handling
What is main/primary memory management(OS COMPONENTS?)
Array of words or bytes
- *allocates and deallocates memory, loads
- processes and keeps track of memory in use.
Major activities in memory management
Keep track of memory in use and by whom
Load processes when memory space becomes available
- Allocates and deallocates memory space as
- Stores files in secondary disks for long
- term storage
What is a file?
- A file is a collection of related
- information as defined by the user
Main activities of OS in file management
Creation and deletion of files
Creation and deletion of directories
Mapping files in secondary storage
- Back up of data on stable storage
- Support for primitives for manipulating
- files and directories
I/O system management
- Manages specific hardware on behalf of the
What are primitives?
- Basic interface or segment of code that can
- be used to build more sophisticated program elements or interfaces.
Secondary storage management
- Manages free space, allocates storage space
- and schedules requests for memory accesses
Address spaces are?
Locations on storage
Three major activities of OS in secondary storage management
- Managing free space available on secondary
- Allocation of storage space when new file
- have been written
Scheduling requests for memory access
Networking (OS components)
- Manages a collection of processors that do
- not share memory, clock or peripheral devices in a distributed system, through
- communication lines called networks
Protection system (OS components)
- Mechanism for controlling the access of
- programs, processes or users to resources defined by the computer system.
Command interpreter system
- An interface of OS with user, which allows
- the user to execute programs through commands.
Function of a command interpreter system
- Gets and executes the next user specified
Advantages to separating command interpreter from kernel
- Ability to change the way the CI looks.
- Which can not be done in kernel
- To prevent malicious processes that gain
- access to certain parts of the kernel from gaining access to the CI
What is a graphic user interface?
- Is a type of interface that allows the user
- to interact with an electronic device using images (icons) rather than text.
- *used in hand-helds, gaming devices, mp3
How does a graphic user interface work?
- Uses graphical representation of
- information and actions available to the user, plus visual indicators such as
- secondary notations as opposed to text based interfaces that use typed command
- label or text navigation
What is a command line interface?
- Form of interaction with a computer
- system/program were a user issues commands in form of command line
- Distinct programs supplied with the OS.
- That use text interfaces called, CLI, Command processor or shell
What is shell in principle?
- Any program that constitutes a user
- interface. Including graphical ones like EXPLORER.EXE
Usage of CLIs
Fast entry of text over pure GUI
- Systems with insufficient resources to
- support GUI
- Often used by programmers, techs system
- admins in engineering and scientific environment. Also people with visual
- System requirement: hardware and software
- components needed for the OS to run efficiently
Types of system requirement
What are recommended system requirement?
- Recommended by manufacturers, often
- significantly higher than requirements needed to run system. *better guidelines
- than minimal in order to have a fully usable and enjoyable experience with the
What are hardware requirements
Physical computer resources required to run a computer program/software efficiently
Hardware compatibility list (HCL)
- List of tested, comparable sometimes
- incompatible hardware devices for the particular OS
Computer architecture is?
- Structure, behaviour and design of
*OSs are designed for particular computer architecture*
Processing power (Hardware requirements)
Processing power is a measurement of how powerful this chip is, i.e. how fast it can do the required calculations. Is fundamental to efficient running of OS
Memory (Hardware requirements)
- RAM and how it’s used is considered when
- defining requirements.
How is secondary storage vital to OS components
- HDD requirements vary depending on size of
Display adapters (Hardware requirements)
- Software requiring a better than average
- computer graphics display, like graphic editors and high end games display
- adapters in system requirements
Peripherals (Hardware requirements)
- Some software needs extensive use of dome
- peripherals demand higher functionality.
What are minimum system requirement?
These are the minimum requirements for basic functionality
3 major types of application CLIs
- Interactive command line sessions
- OS inter-process communication