Download Operating Systems

The Operating System
Operating Systems (F)
• What you need to know about
– operating system as a program;
– directory/folder
Operating Systems (G)
• What you need to know about
– interactive system;
– real-time systems;
– types of file: data files and programs.
Operating Systems (C)
• What you need to know about
– HCI for the user.
– file management, memory management,
error reporting
– interactive systems with background job
capability;
– device drivers
– hierarchical filing system;
– sequential and random/direct access
The Operating System
• The operating system (OS) is the most
important program used by the computer.
– The OS in most modern computers is stored on
hard disc and is loaded into RAM when the
computer starts up.
– Some computers store their OS in ROM (e.g.
some palmtop computers) ROM operating
systems load very quickly (quicker than RAM
OS) and they cannot be erased by accident.
The Operating System
– The operating system controls and
monitors the operation of the computer
system.
– The filing system is part of the OS and it
controls the loading and saving of
programs and data from backing storage.
Current Operating Systems
• Examples of operating systems which are disc
based
– Windows XP for the PC
– System X for Apple Macintosh
– Linux for large fileservers and networks.
Current Operating Systems
• Examples of operating systems which are ROM
based
– JavaOS for Network Computers (NCs)
– PalmOS or Windows Mobile for palm top
and handheld devices (computers,
phones, MP3 players etc.).
Standard Functions of the OS.
• User interface
– the OS provides the means of
communicating with the computer
system (Icons, commands etc. are all
provided by the operating system).
• Manages memory
– The way that memory is allocated to
programs is controlled by the OS. How
much RAM each program gets.
Memory Management
• There is a limited amount of RAM to
store programs in e.g. 1024mb
• If the OS takes up 512mb that leaves
512mb for storing any other program
such Internet Explorer and Microsoft
Word.
Memory Management
• As there is a limited amount of RAM
as you open more and more programs
the RAM allocated to each gets less
and less.
• The less RAM a program has the
slower it will run. The more RAM a
program has the quicker it will run.
Memory Management
• RAM is used to store the parts the
program which are going to be used
next. These have loaded from hard
disc.
• If there is little room in RAM to store
these instruction they have to be
loaded from hard disc which is a much
slower process
Memory Management
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Standard Functions of the OS.
• Controls input/output
– The access to all devices attached to the
computer is controlled by the OS. For
example, the OS can stop two programs
trying to use the same device at the
same time.
Standard Functions of the OS.
• Filing System
– The filing system manages backing storage
– The access to all types of backing storage
devices is controlled by a special part of the
operating system called the filing system.
– The filing system will prevent two programs
trying to access the same files at the same time.
• Error Reporting
– When an error occurs the operating system
provides information to the user about what has
happened and, sometimes, how it can be fixed.
Resource allocation
• When a computer is running the
demands on the systems resources
(i.e. memory, input/output devices,
backing storage etc.) may be greater
than the resources available. To deal
with this a resource allocation system
is built into the OS.
Resource allocation
• Various techniques are used to prevent two
programs demanding the same resource at
the same time (e.g. two programs can't
both send files to the printer at the same
time).
• The resource allocation system also
ensures that all programs running on the
system receive as much processing time as
possible.
OS - Different modes of
processing
• Interactive
• Accepting input from a human.
• Interactive computer systems are programs that
allow users to enter data or commands.
• Most popular programs, such as word processors
and spreadsheet applications, are interactive.
• In interactive processing, the application responds
to commands as quickly as it can once they have
been entered.
• Sometimes there is a delay while the processor
finishes another task.
OS - Different modes of
processing
• Real Time
• Real-time operating systems are systems
that respond to input immediately.
• Automatic teller machines for banks are an
example of real time processing.
• Real time systems are used for tasks such
as navigation, in which the computer must
react to a steady flow of new information
without interruption.
OS - Different modes of
processing
• Interactive systems with background job capability
• Some operating systems allow a background
process to occur at the same time as a foreground
interactive process.
• The foreground process is the one that accepts
input from the keyboard, mouse, or other input
device. Background processes cannot accept
interactive input from a user, but they can access
data stored on a disk and write data to the video
display unit.
• For example, some word processors print files in
the background, enabling you to continue editing
while files are being printed.
Data files and Programs
• A program can be an application like a database or
word processing program
• A data files is something that is created using an
application program like a new word processing
document
• You cannot use the data file unless the application
program that created it is also there
• All computers can read simple text files or ASCII
files, that’s why all computers can read emails no
matter what application is used to compose the
email
Hierarchical filing system
• A filing system in which directories
have files and subdirectories beneath
them
• A hierarchical filing system is one that
uses directories to organise files into a
tree structure.
• Directories (folders) can store more
folders and/or files
Hierarchical filing system
Computer
C:/
D:/
D:/
Drives
Folders
Files
A Hierarchical Filing Structure
Types of Access
• Random Access (also called Direct Access)
devices retrieve the data you want straight
away e.g. CD-ROM drive, Hard disc drive,
floppy disc drive.
• Sequential (also called Serial) devices have
to move through all the data, record after
record, to find the data you need e.g.
Cassette tape, magnetic tape.
Types of access
• Sequential Access
– To go from file A to file Z in a sequentialaccess system, you must pass through
all intervening files.
– Sequential access is sometimes called
serial access.
Types of access
• Random Access
– Refers to the ability to access data at
random. In a random-access system,
you can jump directly to file Z. Disks are
random access media, whereas tapes
are sequential access media.
Device Drivers
• Computer operating systems are written by
software companies e.g. Apple, Microsoft
etc.
• It is impossible for these companies to
know about every single item of hardware
that has been or might be developed for
their operating system.
• To get round this problem the manufacturer
of an item of hardware writes a small
program called a “device driver” for their
device.
Device Drivers
• A device driver program includes
instructions for the operating system
about how to communicate with the
hardware device.
• A printer driver takes the codes used
in the document and translates them
into code the printer understands