Download Sec (3.2)

Sec (3.2)
Operating System Architecture
OS
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Software dividing into two
categories:
1.
2.
Application software
System Software

Operating System
 Translators

Application software:
Consists of programs for performing tasks particular to machine's
utilization

System Software:
Performs those tasks that are commonly to computer systems in
general
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Components of Operating
System:
1.



An operating system must be able to communicate
with users, the portion of operating system that handles
this communicate is called Shell = Graphical User
Interface (GUI)
Shell is the interface between a user and the real heart
of the OS
An important component within the GUI shells is
Window Manager
Which allocates block of space on the screen, call
windows and keeps track of which application is
associated with each window
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Shell = Graphical User Interface
(GUI)
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2) The other component of OS is
called Kernel:


1.
2.
3.
4.
5.
which contains those software components that
perform the very basic functions required by the
computer installation.
The components of kernel is :
File Manager
Device drivers
Memory Manager
Scheduler
Dispatcher
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1) File manager:

Whose job is to coordinate the use of the
machine's mass storage facilities.


The file manager maintains records of all the files
stored in mass storage, including where each file is
located, which users are allowed to access the
various files and which portion of mass storage are
available for new files or extensions to existing files.
Those records are kept on the individual storage
medium containing the related files
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1) File manager:
 So
is placed on-line for each time, the file manager
can retrieve them and thus know what is stored in that
particular medium
 File managers allow files to be grouped into a bundle
called directory or folder
 Directory path: a chain of directions within directions
 File descriptor: if the file manager approves the
requested access, it provides the information needed
to find and manipulate the file . this information is
stored an area of main memory called file descriptor
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2) Device Drivers:


The another component of kernel, which are
the software units that communicates with the
controllers to carry out operations on the
peripheral devices attached to the machine.
Each device driver is uniquely designed for its
particular type of device (printer, disk drive,
monitor) and translate generic requests into
the more technical steps required by the
device assigned to that driver.
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3) Memory Manager:
 Which
is charged with the task of coordinating the
machine's use of main memory
 Such duties are minimal in an environment in which a
computer is asked to perform only one task at a time
 In these cases, the program for performing the current
task is placed at a predetermined location in main
memory, executed and then replaced by the program
for performing the next task
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3) Memory Manager:

In multi-user or multitasking environments in
which the computer is asked to address many
needs at the same time
 The
duties of the memory manager are extensive.
 In these cases, many programs and blocks of data
must reside in main memory concurrently.
 Thus , the memory manager must find and assign
memory space for these needs and ensure that the
actions of each program are restricted to the
program's allocated space.
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3) Memory Manager:
 Moreover,
as the needs of different activities
comes and go, the memory manager must
keep track of those memory areas no longer
occupied
 The task of the memory manager is
complicated further when total main memory
space required exceeds the space actually
available in the computer.
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3) Memory Manager:
 In
this case the memory manager may create
the illusion of additional memory space by
rotating programs and data backs and forth
between main memory and mass storage (a
technique called paging)
 Virtual memory: the large memory space
created by the paging
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Time sharing:


Which is the technique of dividing time into
intervals and then restricting the execution of a
job to only one interval at a time. At the end of
each interval, the current job is temporarily set
aside and another is allowed to execute during
the next interval by rabidly shuffling. The jobs
executing simultaneously is crated
Time-sharing is used in single-user as well as
multi-user
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Time-sharing between process A
and process B
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Continue:




Multitasking = multiprogramming:
Using the idea of time share in single user to
execute multi program
Multi-user:
It is to make user feel that he is the only user.
This system is to some how serve several users
simultaneously . this happens by specifying a
time slice which according to it the user is
served and then switched to another user till the
user is finished.
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4) + 5) Scheduler and Dispatcher :

Scheduler : determines which activities
are to be considered for execution (in
time-sharing system)

Dispatcher : controls the allocation of
time to these activities
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Booting process:

The program stored in ROM called
Bootstrap
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The booting process:
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