Faizan Ali
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Interrupts
The parts of an operating
system all exist in order to make the different parts of a computer work
together. All user software needs to go through the operating system in order
to use any of the hardware, whether it be as simple as a mouse or keyboard or
as complex as an Internet part.
Kernel
This has the task of loading the application into
memory. making sure they do not interfere with one another and allowing them to
share use of the cpu efficiently. the kennel also handles file storage to and
from secondary storage devices such as hard disk and optical drives
.in other words the kernel handles
loading/unloading
application from memory
scheduling
tasks to run on the cpu
memory management
file management
data security
the
single user, single application operating system does not have to deal with
networking. unlike
the server base operating system, and on other hand , a device such as a mobile
phone will
have to have an extremely efficient memory management kernel as its memory is a
very limited resource.
so the kernel of each type of operating system will have been designed with
different duties
in mind.
Device Drivers:
every piece of hardware that makes up
the computer or connected to it. will have a device driver that
allows the operating system to control and communicate with it. There could be
hundreds of devices drivers
pre-installed with the operating system, and the right one for that particular
computer set-up is
loaded on boot-up. the exact detail of which device driver is needed by the
operating system is kept in a
file- in window the file is called is called ''registry' and in Linux the
details will be stored as a number of 'configuration files'. makers of printers, graphic tablets,
scanner, digital cameras and so on, will normally provide device drivers
for each make of operating system. a device driver for window xp is different
from the device driver of Linux this is why if u remove an operating system
such as vista from a hard disk and install Linux instead, u will need to make
sure u
have all the correct drivers available for each piece of hardware.
User interface or (Graphic User Interface):
this part of operating system
that user will see on screen (via the device driver) and reacting to your key presses
and other inputs. The user interface could be the basic command line interface,
as u might find on a server, or it might be a full blown
Graphical User Interface (GUI) such as perhaps gnome on lunix, window vista, or
xp. Graphical user interfaces, such as Microsoft
Windows and the one used by the Apple Macintosh, feature the following basic
components:
Pointer:
A symbol that appears on the
display screen and that you move to select objects and commands. Usually, the
pointer appears as a small angled arrow. Text processing
applications, however, use an I-beam pointer that is shaped like a capital I.
The pointer is controlled by a pointing device such as
a mouse, trackball, joysticks, touchpad’s, and light pens.
Icons:
Small pictures that represent
commands, files, or windows. By moving the pointer to the icon and pressing a
mouse button, you can execute a command
or convert the icon into a window. You can also move the icons around the
display screen as if they were real
objects on your desk.
Desktop:
The area on the display screen where
icons are grouped is often referred to as the desktop because the icons are
intended to represent real objects on a real desktop.
Windows:
You can divide the screen into different areas. In each window, you can run a
different program or display a different information You can move windows around the display
screen, and change their shape and size at will. Menus: Most graphical user interfaces let
you execute commands by selecting a choice from a menu.
Modes:
Modern CPUs support multiple modes
of operation. CPUs with this capability use at least two modes: protected mode
and supervisor mode. The supervisor mode is used by the operating system's
kernel for low level tasks that need unrestricted access to hardware, such as
controlling how memory is written and erased, and communication with devices
like graphics cards. Protected mode, in contrast, is used for almost everything
else. Applications operate within protected mode, and can only use hardware by
communicating with the kernel, which controls everything in supervisor mode.
CPUs might have other modes similar to protected mode as well, such as the
virtual modes in order to emulate older processor types, such as 16-bit processors on
a 32-bit one, or 32-bit processors on a 64-bit one
Program execution
The operating system
provides an interface between an application program and the computer hardware,
so that an application program can interact with the hardware only by obeying
rules and procedures programmed into the operating system. The operating system
is also a set of services which simplify development and execution of
application programs. Executing an application program involves the creation of
a process by the operating system kernel which assigns memory space and other resources,
establishes a priority for the process in multi-tasking systems, loads program
binary code into memory, and initiates execution of the application program
which then interacts with the user and with hardware devices
Interrupts
Interrupts are central to operating systems, as they
provide an efficient way for the operating system to interact with and react to
its environment. The alternative — having the operating system
"watch" the various sources of input for events (polling) that
require action — can be found in older systems with very small stacks (50 or 60 bytes) but are unusual in modern
systems with large stacks. Interrupt-based programming is directly
supported by most modern CPUs. Interrupts provide a computer with a way of
automatically saving local register contexts, and running specific code in
response to events. Even very basic computers support hardware interrupts, and
allow the programmer to specify code which may be run when that event takes
place.
When an interrupt is received,
the computer's hardware automatically suspends whatever program is currently
running, saves its status, and runs computer code previously associated with
the interrupt; this is analogous to placing a bookmark in a book in response to
a phone call. In modern operating systems, interrupts are handled by the
operating system's kernel. Interrupts may come from
either the computer's hardware or from the running program.
Security
A computer being secure depends on a number of technologies
working properly. A modern operating system provides access to a number of
resources, which are available to software running on the system, and to
external devices like networks via the kernel.
The operating system must
be capable of distinguishing between requests which should be allowed to be
processed, and others which should not be processed. While some systems may
simply distinguish between "privileged" and "non-privileged",
systems commonly have a form of requester identity, such as a user name. To
establish identity there may be a process of authentication. Often a username must be
quoted, and each username may have a password
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