Article

PRELIM

Introducing Operating Systems

n  Operating System:

n  Part of the computing system that manages all ofthe hardware and software

n  Controls every file, every device, every section of main memory, and every nanosecond of processing time

n  Controls who can use the system and how

n  Computer system consists of:

n  Software (programs)

n  Hardware (the physical machine and its electronic components)

n  Essential managers of an operating system:

n  Memory Manager

n  Processor Manager

n  Device Manager

n  File Manager

n  Each manager both works closely with the other managers and performs its unique role

n  User Command Interface is unique to each operating system

Memory Management

§  The performance of the computer system depends mainly of:

=How much memory is available.

=How it is optimized while jobs are being processed

4 Memory Allocations

1.     Single – User Contiguous Scheme

2.     Fixed Partition

3.     Dynamic Partition

4.     Relocatable Dynamic Partition

1.Single – User Contiguous Scheme – A single user scheme supports one user on one computer running one job at a time. Sharing is not possible.

Ex:

2. Fix Partition – memory divided into many unequal size, fixed partitions each partition has to protected.

Ex:

3. Dynamic Partition- jobs are given only as much memory as the request. Still contiguous are needed. Internal fragmentation problem is solved.

Ex:

4.Relocatable Dynamic Partition- the memory relocates program of which it gather togethere all empty blocks. Compact the empty blocks and makes one. Blocks oof memory large enough the accommodate some or all of the jobs waiting to get in.

Ex:

MIDTERM

Processor Management

-responsible for allocating the processor to execute the incoming jobs, the tasks of those job.

2 Sub managers

1.Job Scheduler

-also known as the high level scheduler.

2.Process Scheduler

-known as low-level scheduler.

Job and Process Status

1.      Hold

2.      Ready

3.      Running

4.      Waiting

5.      Finish

Process Control Blocks(PCB)

-a data structure that contains information about current status and characteristics of a process.

Process Identification

Process Status

Process state: §  Process status word §  Register content §  Main memory §  Resources                                 §  Process priority

Accounting

Process Scheduling Policies

First come,  first serve(FCFS)- a non-preemptive scheduling that handles job according to their arrival time.

Ex:

                

Shortest Job Next (SJN)–a non-preemptive process scheduler algorithm that select the waiting job with the shortest CPU cycle time.

Ex:

             
Priority Scheduling- a non-preemptive process scheduling algorithm that allows for the execution of high priority job before low-priority jobs.

Shortest Remaining time-a preemptive scheduling algorithm similar to SJN.
Ex:

Round Robin-is a preemptive process scheduling algorithm is used extensively in interactive system.

Ex:

Multiple-level Queues- a process scheduling scheme that group jobs according to a common characteristics.

Keys Terms/ Terminologies

A.      Program (Job) – an interactive unit such a a file stored on a disk.

B.      Process (Task)- an instances of execution of a program that is undeniable and controlled by OS.

C.      Processor (CPU)- performs calculation and execution programs.

D.     Interrupt- a hardware signal that suspends execution of a program and activates the execution of interrupt handler.

E.      Queue- a linked list of PCBs that indicates the order which job or process will be serviced.

F.       Preemptive Scheduling Policy- interrupts processing of a job and transfer

G.     Non-preemptive Scheduling Policy- function without external interrupts.

H.     Aging- a policy used to ensure that jobs that have been in the system for a long time in the level queue will eventually complete their execution.

I.        Thread-a portion of a program that can run independently of other portions.

J.        Turnaround time- a system efficiency that tracks the time required to execute a job and return output to the user.

                                                                                  FINAL

                         System Survivability

-the capability of a  system to fulfill it mission in a timely manner, in the presence of attack , failure or accidents.

4 Keys Properties of Survivability

1.       Resistance to attack

2.       Recognition of attack and the extent of damage

3.       Recovery full  and essential services after attack

4.       Adaptation and evolution to reduce effectiveness of  future attacks

Security Breaches

A.)   Unintentional Attack

-          Any breach of security, of modification of data that was not the result of planned intrusions.

B.)   Intentional Attack

      Denial of Service (DOS) Attacks

-this can be done by flooding server with meaningless request or information.

      Browsing

-a system security violation in which unauthorized user are not allowed to search through secondary storage for information they should not have the privileged to read.

      Video tapping

-a system security violations in which unauthorized user monitors or modify user transmission .

      Trapdoors

-unspecified and undocumented entry point to the system.

Virus- a system written to alter the way of computer operates , without permission or knowledge of the user.

A Virus must meet 2 criteria:

a)    It must be self-executing

b)    It must be self-replicating

A.    Worm –a computer program that replicates itself and is self-propagating in main memory.

B.    Trojan Horse- a malicious computer  with unintended by the user who execute the program.

C.    Bombs

Ø  Logic Bombs

-is a destructive program with a full.

Ø  Time Bombs

-similar to logic bomb but is triggered by a specific time.

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Antivirus Software

            -software that is designed to detect & recover from attacks by viruses & worms.

Firewalls

              -a set of hardware and software designed to protect a system by disguising it TP address from outsiders who don’t have authorization to access it.

Authentication

                -is verification that an individual trying to access a system is authorized to do so.

Encryption

                 -translation of a message or data item from its original from to an encoded form.