Operating system:a collection of programs which control the resources of a computer systemwritten in low-level languages (i.e. machine-dependent)an interface between the users and the hardwareWhen the computer is on, OS will first load into the main memoryAllows convenient usage; hides the tedious stuffAllows efficient usage; parallel activity, avoids wasted cycles
Process Management – Managing the programs that are running.Memory Management – Managing and rationing the memory between processes and data.Storage Management – Managing the permanent Storage of data on disks or other mediaI/O Management – Managing the input and outputDevice / Resource Management – Managing devices and resources and allowing the users to share the resourcesSecurity and Protection – Securing the system against possible unauthorized access to data or any other entity. Protecting the parts of the system against damage.Booting the System and getting it ready to work.Data communications – Providing interface to connect to other computers or allowing others to
Batch operating system:Jobs, together with input data, are fed into the system in a batch. The jobs are then run one after another.No job can be started until previous job is completedTime Sharing Operating System:Each user is given a time slice to interact with the CPU. The size of the time slice will depend on the system.Each user is served in sequence.Real time operating system:immediate response is needed.For example anti-missile defense systemairplane landing control systeminterrupt error in computer system
Multitasking operating systemTo handle 2 or more programs at the same time from a single user ‘s perceptionCPU can only perform one task at a time, however, it runs so fast that 2 or more jobs seem to execute at the same time Multiprogramming2 or more programs store in the main memory at the same timewhen one job reeds to wait (e.g. I/O operation), CPU switch to another job to executewhen the first job finishes waiting, CPU will get back the first job to executeBufferinga temporary storage area (buffers) to read data from input device or send data to the output devicekeep CPU busybecause I/O operation is slow.Spooling:a larger buffer from hard diskbuffer store the data through I/O operationbecause I/O operation is slow and CPU operation is fast .Parallel processing:use 2 or more CPUs to handle jobscomputer networking
Some well known security threatsViruses – These are malicious codes that believe in infecting some data and spread. They generally come from infected removable storage media (floppies, CD’s) or recently they are also coming with mails on the internet. The viral code is generally executed by the user unknowingly. They reside as a part of some important program, file or metadata (Partition Table, Boot Sector etc.) and are activated whenever the innocent infected data is read or executed. When active it tries to search for other such files or data where it can copy itself. Trojans – These are sent to a person by an intruder on purpose. The program is sent with some innocent looking program or file and the user runs it unknowingly. The program when active acts as a server. The intruder can connect to it from the remote machine and command it to do malicious jobs in the recipient's computer.Worms – These consist of two parts one is called the loader and the other is the worm itself. The loader is rather innocent program which is sent to somebody on the network. This loader later on loads the worm onto this computer. Whenever the worm finds that the network is on it sends the loader to the connected machines and thus it spreads.
It is a set of program that provide an
interface between hardware, software
and users and manages all the resources
and provide platform where user can
execute all application/program easily.
Controls peripheral devices connected to the computer
Transfers files between main memory and secondary
storage, manages file folders, backup of file ,recovery
of file, protection of file.
Allocation and deallocation of memory space.
Decide which process load onto memory when memory
Space become available.
Provide the interface b/w hardware, software and
Network Operating System
UNIX / Linux / MS Windows2000 Server
Desktop Operating System
MS Windows 9X/Me / Mac OS / DOS
Mobile Operating System
Palm OS and Pocket PC
Real time processing
Time sharing processing
•Immediate response is needed.
anti-missile defense system
airplane landing control system
interrupt error in computer system
time spent to execute its programs should be
small in size
memory occupied should be as small as possible
Kernel: Core components of the OS
Determines when and for long each process executes
Determines when and how memory is allocated to
Decides what to do when main memory is full
Organizes named collections of data in persistent
Enables processes to communicate with one another
There are various types of intruders
Naïve Users – These are kind of people who have a long
nose and have nothing to do. They know less but keep on
checking out places for other people’s data (Mails etc.).
Skilled Users – These are people like inquisitive students
who are more or less skilled and try out ways to access
things they are not meant to just for fun or to learn.
Purposeful Intruders – These people do nasty jobs on
purpose – e.g. Hacking the Military Data of enemy nation,
Hacking confidential data of the rival company, etc.
Good passwords – Mixture of numbers, letters of different case is a good
security measure. Passwords ideally should not carry any personal information.
These steps make it difficult to guess passwords.
Periodically changing passwords – Some systems allow us to specify
passwords and specify some period within which the password will have to be
Recursive Passwords – This is a technology in which each time a password is
used, it is re-encrypted or changed automatically. The user is given a list of
passwords for a period of time. If that list is secured, the user’s data is secured.
Operating system book by galvin