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
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:
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.
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.
*********************************************
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.
