Operating systems

1. OPERATING SYSTEM
TOPICS COVERED:
INTRODUCTION TO OS
MEMORY MANAGEMENT
PROCESS MANAGEMENT
FILE MANAGEMENT
DEVICE MANAGEMENT

2. WHAT IS OS?
• DEF: An Operating System is a system software
which acts as an interface between the user
and the computer in order to provide an
environment for the user to interact with the
computer and execute programs.

3. WHAT IS OS?
• An Operating System is viewed as a Resource
Allocator or Resource Manager.

4. Examples Of OS

5. FUNCTIONS OF OS
• Following are some of important functions of an
operating System.
• Memory Management
• Processor Management
• Device Management
• File Management
• Security
• Control over system performance
• Job accounting
• Error detecting aids
• Coordination between other software and users

6. MEMORY MANAGEMENT
An Operating System does the following activities for
memory management −
• Keeps tracks of primary memory, i.e., what part of
it are in use by whom, what part are not in use.
• In multiprogramming, the OS decides which
process will get memory when and how much.
• Allocates the memory when a process requests it
to do so.
• De-allocates the memory when a process no
longer needs it or has been terminated.

7. MEMORY MANAGEMENT SCHEMES

12. SEGMENTATION

14. SEGMENTATION

15. SEGMENTATION

16. PROCESS MANAGEMENT

17. ASSIGNMENT QUESTIONS
• ASSIGNMENT QUESTIONS:
• 1.Explain various Addressing modes
• 2.Explain various phases of a compiler?
• 3.Explain various advantages and Disadvantages
of Memory management schemes respectively.
• 4.Explain the life cycle of a process.
• 5.Write any difficult concept from the two units.

32. BASIC TERMINOLOGY
• classic processA process with only one thread.context switchSwitching from running a user level process to the OS kernel and often to other
user processes before the current process is resumed. See CPU Response to InterruptsCPU schedulingDetermine which process in memory is
executed by the CPU at any given point.critical sectionA portion of a program that modifies a shared resources. If other processes or threads
also modify the shared resource at the same time, data inconsistencies could occur.
• See also
• Data Inconsistency
• deadlockThe condition where two or more processes are not able to continue because they are waiting on each other to either release a
resource or do something, but that will not happen because they are waiting on the other.demand pagingA virtual memory management
scheme where the pages of process are loaded only as they are needed.logical addressThe memory address used internally within each
process. This address space is contiguous and usually begins at zero and can extend to the largest address allowed (4GB for 32 bit systems).
Also called virtual address.memory managementKeeping track of what programs are in memory and where in memory they reside.monitorAn
abstract data type for which only one process/thread may be executing of of its member procedures at any given time.multiprogrammingThe
technique of keeping multiple programs in main memory at the same time. These programs compete for access to the CPU so that they can
executemutual exclusionAllowing only one process to access a critical section at one time.page faultA CPU generated trap occuring a
referenced physical memory frame is not currently loaded in physical memory.processAn instance of a program in execution. A thread may
contain one or more thread.process managementKeeping track the progress of processes and all of their intermediate states.process control
blockA data structure in the OS kernel’s memory holding all data that the OS needs about a process. All of the process control blocks are kept in
an array indexed by the PID for each process. See CPU Response to Interrupts, Process Control Block (PCB).process schedulingThe act of
determining which process in the ready state should be moved to the running state. That is, decide which process should run on the CPU
next.physical addressThe memory address used to locate data in the computer’s physical memory banks.race conditionWhen correct execution
depends on the timing of processes or threads running a critical section of code.semaphoreA fundamental locking mechanism that can be used
to allow a varied number (1 is the default) of processes or threads access to a critical section.starvationWhen a lower priority item is unfairly
delayed by higher priority items that arrive later. This can occur in both The Process Scheduler and disk scheduling.system callA request from an
application program for the operating system to perform some hardware action on behalf of the application. System calls are initiated with a
software interrupt assembly language instruction. The argument to the interrupt instruction is a number, which corresponds to the index of an
array in the OS kernel with pointers to the functions that provide the requested service.
• See also
• System Calls
• threadThe basic unit to which the operating system allocates processor time. A thread can execute any part of the process code, including parts
currently being executed by another thread.virtual addressSee logical address.virtual machineThe allusion provided to each process that they
are the only process running on the computer.virtual memoryMemory on a secondary storage device, such as a hard drive or solid state drive,
that augments the computer’s physical radom access memory. Virtual memory is used to give the computer users the benefit of more memory
than is physically present in the computer.