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Showing posts from 2016

Process Scheduling

Process Scheduling The act of determining which process in the ready state should be moved to the running state is known as Process Scheduling.
The prime aim of the process scheduling system is to keep the CPU busy all the time and to deliver minimum response time for all programs. For achieving this, the scheduler must apply appropriate rules for swapping processes IN and OUT of CPU.

Process Scheduler

The process scheduler is the component of the operating system that is responsible for deciding whether the currently running process should continue running and, if not, which process should run next. There are four events that may occur where the scheduler needs to step in and make this decision:
The current process goes from the running to the waiting state because it issues an I/O request or some operating system request that cannot be satisfied immediately.The current process terminates.A timer interrupt causes the scheduler to run and decide that a process has run for its allo…


PROCESS CONTROL BLOCKProcess Control Block (PCB, also called Task Controlling Block, process table, Task Struct, or Switchframe) is a data structure in the operating system kernel containing the information needed to manage a particular process. There is a Process Control Block for each process, enclosing all the information about the process. It is a data structure, which contains the following : Process State - It can be running, waiting etc.Process ID and parent process ID.CPU registers and Program Counter. Program Counter holds the address of the next instruction to be executed for that process.CPU Scheduling information - Such as priority information and pointers to scheduling queues.Memory Management information - Eg. page tables or segment tables.Accounting information - user and kernel CPU time consumed, account numbers, limits, etc.I/O Status information - Devices allocated, open file tables, etc.

Process and Process State

What is a Process? A program in the execution is called a Process. Process is not the same as program. A process is more than a program code. A process is an 'active' entity as opposed to program which is considered to be a 'passive' entity. Attributes held by process include hardware state, memory, CPU etc.

PROCESS STATE Processes can be any of the following states :

New - The process is in the stage of being created.Ready - The process has all the resources available that it needs to run, but the CPU is not currently working on this process's instructions.Running - The CPU is working on this process's instructions.Waiting - The process cannot run at the moment, because it is waiting for some resource to become available or for some event to occur.Terminated - The process has completed.

Difference Between Primary and Secondary Memory

Difference between Primary and Secondary Memory

Primary Memory Secondary Memory These are semiconductor memories.These are magnetic and optical memories.They are characterized as volatile random access memories (RAM) or on-volatile memories (ROM).They are non-volatile.They contain program and data that is currently being used by micro processor.These are used to for bulk storage.These memories are fast enough to interact with the microprocessor.Slower than primary memories.Also known as Main MemoryAlso known as Backup Memory or Auxiliary Memory. E.g. Tapes, Floppies, Hard Discs, CD ROMs, DVDs

Secondary Memory

Secondary Memory/Non Volatile Menory

Secondary memory (or secondary storage) is the slowest and cheapest form of memory. It cannot be processed directly by the CPU. It must first be copied into primary storage (also known as RAM).
Secondary memory is computer memory that is non-volatile and persistent in nature and is not directly accessed by a computer/processor. It allows a user to store data that may be instantly and easily retrieved, transported and used by applications and services.
Secondary memory is also known as secondary storage. Secondary memory devices include magnetic disks like hard drives and floppy disks ; optical disks such as CDs and CDROMs ; and magnetic tapes, which were the first forms of secondary memory.
Secondary memory is slower than primary memory but can store and retain data, even if the computer is not connected to electrical power. It also has substantial storage capacities, ranging from some MBs to several TBs of storage…

Primary Memory

Primary Memory / Volatile Memory: Primary Memory also called as volatile memory because the memory can’t store the data permanently. Primary memory select any part of memory when user want to save the data in memory but that may not be store permanently on that location. It also has another name i.e. RAM.
Random Access Memory (RAM): The primary storage is referred to as random access memory (RAM) due to the random selection of memory locations. It performs both read and write operations on memory. If power failures happened in systems during memory access then you will lose your data permanently. So, RAM is volatile memory. RAM categorized into following types.
DRAMSRAMDDRRAM (Dual Data Rate RAM) Read Only Memory (ROM) : ROM is permanent memory location that offer huge types of standards to save data. But it work with read only operation. No data lose happen whenever power failure occur during the ROM memory work in computers.
ROM memory has several models such names are foll…

Memory (Computer)

Memory (Computer)

Computer memory is any physical device capable of storing information temporarily or permanently. For example, Random Access Memory (RAM), a memory that stores information on an integrated circuit. Moreover, the term memory is usually used as a shorthand for physical memory, which refers to the actual chips capable of holding data. Some computers also use virtual memory, which expands physical memory onto a hard disk. Every computer comes with a certain amount of physical memory, usually referred to as main memory or RAM. You can think of main memory as an array of boxes, each of which can hold a single byte of information. 

Types of Computer Memory:Memory is the best essential element of a computer because computer can’t perform simple tasks. The performance of computer mainly based on memory and CPU. Memory is internal storage media of computer that has several names such as majorly categorized into two types, Main memory and Secondary memory.
1. Primary Memory /…