OS101MODULE1-2

• An Operating System is a collection of software

  that manages computer hardware resources and

  provides common services for computer programs.
• An Operating System is an interface between a computer user

  and computer hardware.
• Memory management refers to management of Primary Memory or Main Memory.
• Main

  memory is a large array of words or bytes where each word or byte has its own address.
• Main memory provides a fast storage that can be accessed directly by the CPU. For a program

  to be executed, it must in the main memory.
• In multiprogramming environment, the OS decides which process gets

  the processor when and for how much time. This function is

  called process scheduling.
• A file system is normally organized into directories for easy navigation

  and usage.
• Security By means of password and similar other techniques, it prevents

  unauthorized access to programs and data.
• Control over system performance Recording delays between request for a

  service and response from the system.
• Job accounting Keeping track of time and resources used by various jobs and

  users.
• Error detecting aids Production of dumps, traces, error messages, and other

  debugging and error detecting aids
• Coordination between other software’s and users Coordination and assignment

  of compilers, interpreters, assemblers and other software to the various users of

  the computer systems.
• Time-sharing is a technique which enables

  many people, located at various terminals, to

  use a particular computer system at the same

  time.
• Time-sharing or multitasking is a logical extension of multiprogramming. Processor's time which is shared among multiple users simultaneously is termed as time-sharing.
• Distributed systems use multiple central processors to serve multiple real-time applications and multiple users. Data processing jobs are distributed among the processors accordingly.
• The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines). These are referred as loosely coupled systems or distributed systems.
• A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions.
• A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment.
• The time taken by the system to respond to an input and display of required updated information is termed as the response time.
• Soft real-time systems are less restrictive. A critical real-time task gets

  priority over other tasks and retains the priority until it completes.

  Soft real-time systems have limited utility than hard real-time

  systems.
• An I/O subsystem comprises of I/O devices and their

  corresponding driver software. Drivers hide the peculiarities

  of specific hardware devices from the users.
• A file represents a collection of related information.
• A file system is normally organized into directories for easy

  navigation and usage.
• COMMUNICATION In case of distributed systems which are a collection

  of processors that do not share memory, peripheral

  devices, or a clock, the operating system manages

  communications between all the processes.
• ERROR HANDLING

  Errors can occur anytime and anywhere. An error may occur

  in CPU, in I/O devices or in the memory hardware.
• RESOURCE MANAGEMENT

  In case of multi-user or multi-tasking environment,

  resources such as main memory, CPU cycles and files

  storage are to be allocated to each user or job.
• A program is a piece of code which may be a single line or million of lines