Chapter 1 part 3

Hassan Bin Ali
Department of IT & Communication
Politeknik Tuanku Syed Sirajuddin

FP202 Fundamental of OS

 By the end of this lecture, students will be able to:
1) Explain terminologies relating to operating
system
2) Describe components of operating system
3) Identify different interfaces of operating
system
4) Describe relations between system calls and
Application Programming Interface (API)


OPERATING
SYSTEM
TERMINOLOGIES


 Process of letting the operating system perform
multiple task at what seems to the user simultaneously.
 The CPU switches from one program to the next so
quickly that appears as if all of the programs are
executing at the same time.
 System with multiple processor
- This is the case, since there are several CPU's to
execute programs on .
 System with single processor
- Multitasking done by switching execution very rapidly
between each program, thus giving the impression of
simultaneous execution.
-This process is also known as task switching or timesharing.


• Goal of multiprogramming is to efficiently
utilize all of the computing resources.
•When a job issues an I/O request (e.g., open
a file, read data from a file), it cannot
continue until the request is fulfilled.
•The CPU then becomes idle (the job is
blocked on the request).


• Logical extension of multiprogramming termed
multitasking.
• Quite often sitting at terminal using a “command line”
interface to interact with computer.
 Types in commands from keyboard.

 A system program called a shell reads command from

the command line and makes OS system calls to carry
out commands.
• Switching between users is very fast.
• Goal is to give the illusion that each user has own machine.


 Buffering is a method of overlapping the
computation of a job with its execution.
 It temporarily stores input or output data in an
attempt to better match the speeds of two
devices such as a fast CPU and a slow disk
drive.
 If, for example, the CPU writes information to
the buffer, it can continue in its computation
while the disk drive stores the information.


• With spooling, the disk is used as a very large buffer.
Usually complete jobs are queued on disk to be completed
later.
•A typical example is the spooler for a printer. When a print
job is issued, the spooler takes care of it, sending it to the
printer if it is not busy, or storing it on disk otherwise.


OPERATING
SYSTEM
COMPONENTS


 Operating system comprises a set of software
packages that can be used to manage interactions with
the hardware.
 The following elements are generally included in this
set of software:
1) Kernel
- Represents the operating system’s basic functions such
as management of memory, processes, files, main
inputs/outputs and communication functionalities.

2) Shell
- Allowing communication with the operating system
via a control language, letting the user control the
peripherals without knowing the characteristics of the
hardware used, management of physical addresses,
etc.


3) File System
- Allowing files to be recorded in a tree structure.


OPERATING
SYSTEM
INTERFACES


 A user interface is the system by which people
(users) interact with a machine. The user interface
includes hardware (physical) and software
(logical) components.
 User interfaces exist for various systems, and

provide a means of:
- Input, allowing the users to manipulate a system,

and/or
- Output, allowing the system to indicate the effects

of the users' manipulation.


 Users may also interact with the
operating system with some kind of
software user interface like typing
commands by using command line
interface (CLI) or using a graphical
user interface.
 For hand-held and desktop
computers, the user interface is
generally considered part of the
operating system.
 On large multi-user systems such
as Unix-like systems, the user
interface is generally implemented
as an application program that runs
outside the operating system.

Operating System
Placement

The user interface has two main components:
◦ Presentation language, which is the computer-to-human
part of the transaction.
◦ Action language that characterizes the human-to-
computer portion.


There are several types of user interfaces:
◦ Command Line Interfaces.
◦ Menu interfaces.
◦ Graphical User Interfaces (GUIs).
◦ Voice User Interfaces.
◦ Web Form Interfaces.


 CLI are often used by programmers and system
administrators, in engineering and scientific
environments, and by technically advanced personal
computer users.
 Examples of CLI application:


 Menu Interface presents user with a menu of
choices.
 Rather than learning specific commands, user
choose them from the menu.
 Menus can contain submenus, in which case user
need to memorize how to access a particular
command.
 This is still much easier than memorizing the
actual command.


 Menu interfaces commonly appear the beginning of
a game, often at the title screen regardless of how
menus are used later in the game.
 Past the opening menu, games often provide an
option menu for saving. While these examples
constitute menu interfaces, many games include
menu interfaces to control entity actions as well.
 Some games provide a series of menus through
which the player controls game entities that is
analogous to menu systems found in interactive
kiosks.


 The sophistication of these menu interfaces ranges from
simple, flat menus to deeply nested menus with many
sub-options.
 The specific representation of menu interfaces can vary
as well, some games representing menus as a series of
graphical buttons, others using text menus.


 Menu interface provides the user with an
onscreen list of available selections.
 A nested menu is a menu that can be reached

through another menu.


 A graphical user interface or GUI (sometimes
pronounced gooey) is a type of user interface item that
allows people to interact with programs in more ways
than typing such as computers
 Examples: hand-held devices such as MP3 Players,
Portable Media Players or Gaming devices; household
appliances and office equipment with images rather than
text commands.
 A GUI offers graphical icons, and visual indicators, as
opposed to text-based interfaces, typed command labels
or text navigation to fully represent the information and
actions available to a user.


 The actions are usually performed through direct
manipulation of the graphical elements.
 Pictures tend to make the interface more intuitive.


Characteristic Description
Windows Multiple windows allow different information to be
displayed simultaneously on the user’s screen.
Icons Icons different types of information. On some systems,
icons represent files; on others, icons represent
processes.
Menus Commands are selected from a menu rather than typed
in a command language.
Pointing A pointing device such as a mouse is used for selecting
choices from a menu or indicating items of interest in a
window.
Graphics Graphical elements can be mixed with text on the same
display.


 A Voice User Interface (VUI) makes human
interaction with computers possible through a
voice/speech platform in order to initiate an
automated service or process.
 The VUI is the interface to any speech application.
 Controlling a machine by simply talking to it was
science fiction only a short time ago.
 However, with advances in technology, VUI have
become more common place, and people are
taking advantage of the value that these hands-
free, eyes-free interfaces provide in many
situations.


 Voice User interface are developing rapidly
 There are two different types of voice recognition:
◦ Continuous speech systems, allowing for dictation.
◦ Speaker independence, so people can enter commands or
words at a given workstation.


 Web Form interfaces are onscreen forms
displaying fields containing data items or
parameters that need to be communicated to the
user.
 Web Form interfaces may be implemented using

the Web.


 A Web Form allows a user to enter data that is sent to a
server for processing.
 Web forms resemble paper forms because internet users
fill out the forms using checkboxes, radio buttons, or text
fields.
 For example, Web Forms can be used to enter shipping
or credit card data to order a product or can be used to
retrieve data (e.g: searching on a search engine).
 In addition to functioning as input templates for new
information, Web Forms can also be used to query and
display existing data in a similar manner to mail merge
forms, with the same advantages.


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RELATION
BETWEEN
SYSTEM CALLS
AND API

 User programs are not allowed to access system resources directly.
They must ask the OS to do that for them.

 OS provides a set of functions that can be called by user programs
to request for OS services. These functions are called “system calls”
 System calls run in kernel mode.
 They can be called by executing a special instruction (trap or
software interrupt) which causes processor to switch to the kernel
mode and jump to a previously defined location in the kernel.
 When the system call finishes, processor returns to the user
program and runs in user mode.


 An API is a set of functions provided by an operating
system or other system software.
 An application program calls the functions to request
the services.
 An API clearly defines how to call functions and what
the results are. (API is specification, not
implementation)
 Examples: APIs for file system, graphics user interface,
networking, etc.


 Portability
◦ User programs that follow the API’s definition are
portable.
 An API can provide a common interface for different
implementations of a service.
◦ For example, the UNIX file system API is the same for
all kinds of devices.
◦ X windows API has many implementations on different
machine architectures
 Using an API allows upgrading system software
without changing user programs


Chapter 1 part 3

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Chapter 1 part 3