Allicient: Operating System

Importaint Concept In Operating System

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<b>Spooling:-</b> Spooling is the process of a sending data to a spool, or temporary storage area in the computer’s memory. This data may contain files or processes. Like a spool of thread, the data can build up within the spool as multiple files or jobs are sent to it. However, unlike a spool of thread, the first jobs sent to the spool are the first ones to be processed (FIFO, not LIFO).<br />
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The most common type of spooling is print spooling, where print jobs are sent to a print spool before being transmitted to the printer. For example, when you print a document from within an application, the document data is spooled to a temporary storage area while the printer warms up. As soon as the printer is ready to print the document, the data is sent from the spool to the printer and the document is printed.<br />
Semaphore:-<br />
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<b>Semaphores</b><b><b>:-</b> </b>These  are commonly use for two purposes: to share a common memory space and to share access to files. Semaphores are one of the techniques for interprocess communication (IPC). The C programming language provides a set of interfaces or “functions” for managing semaphores.<br />
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In programming, especially in Unix systems, semaphores are a technique for coordinating or synchronizing activities in which multiple processes compete for the same operating system resources. A semaphore is a value in a designated place in operating system (or kernel) storage that each process can check and then change. Depending on the value that is found, the process can use the resource or will find that it is already in use and must wait for some period before trying again. Semaphores can be binary (0 or 1) or can have additional values. Typically, a process using semaphores checks the value and then, if it using the resource, changes the value to reflect this so that subsequent semaphore users will know to wait.<br />
<b>Swapping:-</b> Swapping concept comes in terms of process scheduling. Swapping is basically implemented by Medium term scheduler.Medium term scheduler removes process from CPU for duration and reduce the degree of multiprogramming. And after some time these process can again be reintroduced into main memory. Process execution will again be resumed from the point it left CPU. This scheme is called swapping. More generally we can say swapping is removing of process from memory to secondary memory and again back to main memory.<br />
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Spooling:-</h1>
Spooling is the process of a sending data to a spool, or temporary 
storage area in the computer’s memory. This data may contain files or 
processes. Like a spool of thread, the data can build up within the 
spool as multiple files or jobs are sent to it. However, unlike a spool 
of thread, the first jobs sent to the spool are the first ones to be 
processed (FIFO, not LIFO).<br />
The most common type of spooling is print spooling, where print jobs 
are sent to a print spool before being transmitted to the printer. For 
example, when you print a document from within an application, the 
document data is spooled to a temporary storage area while the printer 
warms up. As soon as the printer is ready to print the document, the 
data is sent from the spool to the printer and the document is printed.<br />
<h1>
Semaphore:-</h1>
Semaphores are commonly use for two purposes: to share a common 
memory space and to share access to files. Semaphores are one of the 
techniques for interprocess communication (IPC). The C programming 
language provides a set of interfaces or “functions” for managing 
semaphores.<br />
In programming, especially in Unix systems, semaphores are a 
technique for coordinating or synchronizing activities in which multiple
 processes compete for the same operating system resources. A semaphore 
is a value in a designated place in operating system (or kernel) storage
 that each process can check and then change. Depending on the value 
that is found, the process can use the resource or will find that it is 
already in use and must wait for some period before trying again. 
Semaphores can be binary (0 or 1) or can have additional values. 
Typically, a process using semaphores checks the value and then, if it 
using the resource, changes the value to reflect this so that subsequent
 semaphore users will know to wait.<br />
<h1>
Swapping:-</h1>
Swapping concept comes in terms of process scheduling. Swapping is 
basically implemented by Medium term scheduler.Medium term scheduler 
removes process from CPU for duration and reduce the degree of 
multiprogramming. And after some time these process can again be 
reintroduced into main memory. Process execution will again be resumed 
from the point it left CPU. This scheme is called swapping. More 
generally we can say swapping is removing of process from memory to 
secondary memory and again back to main memory.<br />
<h1>
Paging:-</h1>
Paging is a memory management technique in which the memory is 
divided into fixed size pages. Paging is used for faster access to data.
 When a program needs a page, it is available in the main memory as the 
OS copies a certain number of pages from your storage device to main 
memory. Paging allows the physical address space of a process to be 
noncontiguous.<br />
<h1>
Segmentation:-</h1>
Segmentation is one approach to memory management and protection in 
the operating system. It has been superseded by paging for most 
purposes, but much of the terminology of segmentation is still used, 
“segmentation fault” being an example. Some operating systems still have
 segmentation at some logical level although paging is used as the main 
memory management policy.<br />
<h1>
Thrashing:-</h1>
Thrashing is computer activity that makes little or no progress, 
usually because memory or other resources have become exhausted or too 
limited to perform needed operations. When this happens, a pattern 
typically develops in which a request is made of the operating system by
 a process or program, the operating system tries to find resources by 
taking them from some other process, which in turn makes new requests 
that can’t be satisfied. In a virtual storage system (an operating 
system that manages its logical storage or memory in units called 
pages), thrashing is a condition in which excessive paging operations 
are taking place.<br />
A system that is thrashing can be perceived as either a very slow system or one that has come to a halt.<br />
- See more at: http://localhost:81/test/importaint-concept-in-operating-system/#sthash.U3nbjyNA.dpuf</div>
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Paging is a memory management technique in which the memory is divided into fixed size pages. Paging is used for faster access to data. When a program needs a page, it is available in the main memory as the OS copies a certain number of pages from your storage device to main memory. Paging allows the physical address space of a process to be noncontiguous.<br />
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<b>Segmentation:-</b> Segmentation is one approach to memory management and protection in the operating system. It has been superseded by paging for most purposes, but much of the terminology of segmentation is still used, “segmentation fault” being an example. Some operating systems still have segmentation at some logical level although paging is used as the main memory management policy.<br />
<b>Thrashing:-</b> Thrashing is computer activity that makes little or no progress, usually because memory or other resources have become exhausted or too limited to perform needed operations. When this happens, a pattern typically develops in which a request is made of the operating system by a process or program, the operating system tries to find resources by taking them from some other process, which in turn makes new requests that can’t be satisfied. In a virtual storage system (an operating system that manages its logical storage or memory in units called pages), thrashing is a condition in which excessive paging operations are taking place.<br />
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A system that is thrashing can be perceived as either a very slow system or one that has come to a halt.</div>

Importaint Concept In Operating System

Spooling:- Spooling is the process of a sending data to a spool, or temporary storage area in the computer’s memory. This data may contain...

Process Control Block In Operating System

Theallicient 0 Operating System 15:30

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The OS must know specific information about processes in order to manage, control them and also to implement the process model, the OS maintains a table (an array of structures), called the process table, with one entry per process.These entries are called process control blocks (PCB) – also called a task control block. This entry contains information about the process’state, its program counter, stack pointer, memory allocation, the status of its open files, its accounting and scheduling information, and everything else about the process that must be saved when the process is switched from running to ready or blocked state so that it can be restarted later as if it had never been stopped.</div>
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<br />PCB Such information is usually grouped into two categories: Process State Information and Process Control Information. Including these:<br /><br /> <b>   Process state. </b>The state may be new, ready, running, waiting, halted, and so on.<br /><b>    Program counter.</b> The counter indicates the address of the next instruction to be executed for this process.<br /><b>    CPU registers.</b> The registers vary in number and type, depending on the computer architecture. They include accumulators, index registers, stack pointers, and general-purpose registers, plus any condition-code information.<br />    <b>CPU-scheduling information.</b> This information includes a process priority, pointers to scheduling queues, and any other scheduling parameters.<br />   <b> Memory-management information.</b> This information may include such information as the value of the base and limit registers, the page tables, or the segment tables, depending on the memory system used by the OS.<br />    Accounting information. This information includes the amount of CPU and real time used, time limits, account numbers, job or process numbers, and so on.<br />  <b>  I/O status information.</b> This information includes the list of I/O devices allocated to the process, a list of open files, and so on.<br /><br /></div>
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Process Control Block In Operating System

The OS must know specific information about processes in order to manage, control them and also to implement the process model, the OS mai...

Program v/s Process v/s Thread

Theallicient 0 Operating System 15:27

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<b>What is a Program?</b><br /><br />A program is an executable file residing on the disk (secondary storage) in a directory. It is also termed as a set of instructions stored in the secondary storage device that are intended to carry out a specific job. It is read into the primary memory and executed by the kernel.<br /><br />
<b>What is a process?</b><br /><br />An executing instance of a program is called a process. Some operating systems use the term ‘task‘ to refer to a program that is being executed.<br /><br />A process is termed as an ‘active entity’ since it is always stored in the main memory and disappears if the machine is power cycled. Several process may be associated with a same program.<br /><br />On a multiprocessor system, multiple processes can be executed in parallel. On a uni-processor system, though true parallelism is not achieved, a process scheduling algorithm is applied and the processor is scheduled to execute each process one at a time producing an illusion of concurrency.<br /><br />Example: Executing multiple instances of the ‘Calculator’ program. Each of the instances are termed as a process.<br /><br /><b>What is a thread?</b><br /><br />A thread is called a ‘lightweight process’. It is similar to a real process but executes within the context of a process and shares the same resources allotted to the process by the kernel.<br /><br />A process has only one thread of control – one set of machine instructions executing at a time. A process may also be made up of multiple threads of execution that execute instructions concurrently. Multiple threads of control can exploit the true parallelism possible on multiprocessor systems. On a uni-processor system, a thread scheduling algorithm is applied and the processor is scheduled to run each thread one at a time.<br /><br />All the threads running within a process share the same address space, file descriptor, stack and other process related attributes. Since the threads of a process share the same memory, synchronizing the access to the shared data within the process gains unprecedented importance.<br />- See more at: http://localhost:81/test/program-vs-process-vs-thread/#sthash.fLTVrAGJ.dpuf</div>

Program v/s Process v/s Thread

What is a Program? A program is an executable file residing on the disk (secondary storage) in a directory. It is also termed as a set of i...

Seek Time & Rotational Latency Time In OS

Theallicient 0 Operating System 15:25

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<b>Seek time:-</b><br />The total amount of time required for information on a disk drive to be found. The lower this value is the faster the hard drive will be able to find or read data. Examples of common hard drive seeks times are 8ms and 10ms.<br /><b>Rotational Latency Time:-</b><br />Rotational delay or rotational latency is the time required for the addressed area of a computer’s disk drive (or drum) to rotate into a position where it is accessible by the read/write head. The term applies to rotating storage devices (such as a hard disk or floppy disk drive, and to the older drum memory systems).<br /><br />Rotational delay is one of the three delays associated with reading or writing data on a disk, and somewhat similar for CD or DVD drives. The others are seek time and transfer time. Sometimes spin-up time is considered as an independent fourth factor though it is a rotational delay that only affects systems that automatically spin down (turn off) drives to conserve power, noise, etc..<br /></div>

Seek Time & Rotational Latency Time In OS

Seek time:- The total amount of time required for information on a disk drive to be found. The lower this value is the faster the hard driv...

Differences Between Windows & Linux Operating System

Theallicient 0 Operating System 15:24

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<b>Windows</b></div>
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<td valign="top" width="325"><div align="center">
<b>Linux</b></div>
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<td valign="top" width="313">1.Windows are Open Source software development</td>
<td valign="top" width="325">1.Linux is an example of Open Source software development</td>
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<td valign="top" width="313">2. Microsoft Windows can run between 2000-15000 INR per each license copy.</td>
<td valign="top" width="325">2. The majority of Linux variants are available for free or at a much lower price than Microsoft Windows.</td>
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<td valign="top" width="313">3. The file formats supported by it are FAT, FAT32, NTFS, exFAT.</td>
<td valign="top" width="325">3. It supports wide variety of file formats like Xfs, Btrfs, FAT, FAT32, Ext2.</td>
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<td valign="top" width="313">4. Microsoft Windows is not open source and the majority of Windows programs are not open source.</td>
<td valign="top" width="325">4. Many of the Linux variants and many Linux programs are open source and enable users to customize or modify the code however they wish to.</td>
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<td valign="top" width="313">5. Microsoft windows are less secure.</td>
<td valign="top" width="325">5. Linux operating system are more secure than windows.</td>
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<td valign="top" width="313">6. Windows installationprocess is easy and user friendly.</td>
<td valign="top" width="325">6.Linux operating system installation is difficult as compare to the windows.</td>
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<td valign="top" width="313">7. Although Windows does have software programs, utilities, and games for free, the majority of the programs will cost anywhere between 1200 – 20000+ INR per copy.</td>
<td valign="top" width="325">7. Many of the available software programs, utilities, and games available on Linux are freeware or open source. Even such complex programs such as Gimp, Open Office, Star Office, and wine are available for free or at a low cost.</td>
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<td valign="top" width="313">8. Windows operating system are less reliable but now Microsoft Windows has made great improvements in reliability over the last few versions of Windows, it still cannot match the reliability of Linux.</td>
<td valign="top" width="325">8. The majority of Linux variants and versions are notoriously reliable and can often run for months and years without needing to be rebooted.</td>
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<td valign="top" width="313">9. Windows are generally developed & designed by the Microsoft Corporation.</td>
<td valign="top" width="325">9. Windows are generally developed & designed Linus Torvalds</td>
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<td valign="top" width="313">10. Windows operating system are generally processed by MS-DOS</td>
<td valign="top" width="325">10. Linux operating system are generally processed by Basic Terminal (CLI)</td>
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<td valign="top" width="313">11. Windows are only updated by using Windows updates</td>
<td valign="top" width="325">11. Linux can be easily updated by many methods</td>
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<span class="entry-title">Differences Between Windows & Linux Operating System</span> was last modified: <span class="updated"> December 22nd, 2014</span> by <span class="author vcard"><span class="fn">Allicient</span></span></div>
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Differences Between Windows & Linux Operating System

Windows Linux 1.Windows are Open Source software development 1.Linux is an example of Open Source software development 2. M...

Demand Paging In Operating System

Theallicient 0 Operating System 15:22

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Demand paging is a form of virtual memory, where a page of memory will be paged in if a program tries to access it and the page is not already in the main memory. Therefore, demand paging only loads pages that should be brought into real memory during the execution process, it does not need to swap all the memory for a process from the secondary memory to the main memory during the program start up.<br /><br />The advantage of this process is that, only pages that are needed during the execution process are loaded, so there is more space in the main memory and therefore more processes can be loaded, reducing context switching time, which normally uses up a large amount of memory resources. However, demand paging means that programs can face extra latency when they attempt to access a page for the first time, this process may also be vulnerable to possible security risks such as timing attacks.<br /><br />Demand paging process;<br /><br />1.Program attempts to find a page.<br /><br />2.If the page is located in the main memory then the program runs as normal.<br /><br />3.If the page cannot be located then what is known as a page-fault trap occurs.<br /><br />4.Then the memory reference is checked to determine it is a valid reference to a location on secondary memory, if it is then the page will have to be paged in.<br /><br />5.The desired page is scheduled to be read into main memory.<br /><br />6.This operation is restarted at the point before the page-fault trap occurs. (Steps 1 & 2).<br /><br />7.The program can now access the desired page in the main memory.<br /></div>

Demand Paging In Operating System

Demand paging is a form of virtual memory, where a page of memory will be paged in if a program tries to access it and the page is not alre...

RAID levels In Operating System

Theallicient 0 Operating System 15:21

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<b>RAID</b> (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in different places (thus, redundantly) on multiple hard disks. By placing data on multiple disks, I/O (input/output) operations can overlap in a balanced way, improving performance. Since multiple disks increases the mean time between failures (MTBF), storing data redundantly also increases fault tolerance.<br /><br /><br /><br /><b>TABLE OF CONTENTS:<br />RAID level 0: Striping<br />RAID level 1: Mirroring and performance improvements<br />RAID level 3: Byte-level parity<br />RAID level 4: Block-level parity<br />RAID level 5: Rotating parity<br />RAID level 6: Tolerates failure of two disk drives</b><br /><b>RAID 0</b><br /><br />Technically speaking RAID 0 is not a RAID level, but it is customarily viewed as RAID. Let’s say that you have three disk drives. Instead of writing everything on the first disk drive, you split the data up. So the first chunk of that file would be placed on disk one, the next chunk would be placed on disk two and the final chunk would be placed on disk three. You would then repeatedly rotate around that until the file is actually included on the correct array.<br /><br />You should think of RAID 0 as striping. Essentially, you have broken the file data down into pieces and placed them in the first, second and third arrays until they land in the correct array. Instead of reading the data from one disk drive, you now read the data parallel from all disk drives and then you combine the data on the other end. Essentially, you end up getting the performance of three disk drives and therefore the access of that file is vastly improved. This is classic striping.<br /><br />So the performance factor in RAID 0 improves because you have three disk drives pumping data back at you. There is also no impact on the availability of the data. If one of those three disk drives dies, your whole file is ruined because you do not have any coherent, consistent data, you have a chunk missing.<br /><br /><b>RAID 1</b><br /><br />RAID 1, also known as mirroring, is essentially where you have two disk drives and whatever you put on disk one, you simultaneously put on disk two. The idea is that if one of those two disks dies, then you have the other disk that is still working and therefore you achieve data availability improvements.<br /><br />You can also achieve performance improvements with RAID 1. When everything is functioning correctly — both of the disk drives are spinning, behaving properly and you’re reading data from both disk drives — you’re read performance will improve double for all practical purposes.<br /><br />There is a performance improvement in the situation of read, but not in terms if write. You also achieve extra availability of your data, because if one disk drive dies, you can access your information from the other disk drive.<br /><br /><b>RAID 3</b><br /><br />RAID 3 is the process of gaining up a certain number of disk drives, with the minimum number of drives being three. For this particular example, we’ll use five disk drives. Four of those disk drives would be data disks drives and the fifth would actually be a parity disk drive.<br /><br />The idea is that you have striped the data on the first four disk drives and then you calculate a parity from those drives to be placed on the fifth disk drive. In this type of situation, if any of those single disk drives fail, you can actually re-create that information by using the other four disk drives that are still working.<br /><br />So RAID 3 is very common in large, sequential workloads, such as video files. You want to be able to read a video file very quickly and you want to keep going from one end to the other. Very often, video files prefer to use RAID 3; you lock the first four drives in the example and just start extracting information from those drives in a rapid fashion. Performance and availability both improve greatly because any one of those five disk drives can die, but your data will still be safe.<br /><br /><b>RAID 4</b><br /><br />RAID 4 is very similar to RAID 3 in that a parity disk drive is always one of the five associated disk drives. But the difference is instead of doing the parity at the byte level, in RAID 4, the parity is done at the block level.<br /><br />The difference between RAID 3 and RAID 4 is very minor, and is only really applicable when you start looking at the finer art of RAID systems. Beyond performing parity at the byte level, the amount of data that is considered a chunk also differentiates RAID 4 from RAID 3.<br /><b><br />RAID 5</b><br /><br />RAID 5 is very similar to RAID 3 and is probably the most popular level of the technology. In RAID five, the last disk drive is not the only drive that contains parity data in the array.<br /><br />In RAID 5, you rotate the parity in the five disk drives. So the first array may contain four drives of data and then one drive of parity, then the next array would contain three disks of data and then two disks of parity. In essence, parity is moved around in a round robin-type fashion. All five disk drives have a combination of data and parity.<br /><br />Again, if a single disk drive in that pairing dies, you can re-create that information from the remaining four disk drives. So you can tolerate a single disk drive failure, which improves the availability of data. This also improves performance because you are striping the data on the other four disk drives.<br /><br /><b>RAID 6</b><br /><br />RAID 6 is similar to RAID 5 in terms of striping and parity, with the major difference being that RAID 6 can tolerate two disk drives failing. In RAID 6, up to two disk drives can die and you can still have an efficient level of data availability.<br />- See more at: http://localhost:81/test/raid-levels-in-operating-system/#sthash.oN65zYyb.dpuf</div>

RAID levels In Operating System

RAID (redundant array of independent disks; originally redundant array of inexpensive disks) is a way of storing the same data in differen...

Distributed Operating System & Parallel operating systems

Theallicient 0 Operating System 15:20

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<b>Distributed Operating System:-</b><br /><br />It is a model where distributed applications are running on multiple computers linked by communications. A distributed operating system is an extension of the network operating system that supports higher levels of communication and integration of the machines on the network.<br /><br />This system looks to its users like an ordinary centralized operating system but runs on multiple, independent central processing units (CPUs).<br /><br /><br /><br />                             <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3abUPLSCZtvpPedxQpGI6OmaGX1o2jnjrmDihPV7rk5_WEmlG09OVDt8DcgVolBlaEdc9J6qUNKb4Af61BLK2qhHOlTJYldQdqc9koPt-R0E4FEoCKJxYDlCtjzfTd-qoj8yU7M49Fy-L/s1600/Node_Organization-Distributed_Model@allicient.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="316" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj3abUPLSCZtvpPedxQpGI6OmaGX1o2jnjrmDihPV7rk5_WEmlG09OVDt8DcgVolBlaEdc9J6qUNKb4Af61BLK2qhHOlTJYldQdqc9koPt-R0E4FEoCKJxYDlCtjzfTd-qoj8yU7M49Fy-L/s1600/Node_Organization-Distributed_Model@allicient.png" width="400" /></a><br /><br />These systems are referred as loosely coupled systems where each processor has its own local memory and processors communicate with one another through various communication lines, such as high speed buses or telephone lines. By loosely coupled systems, we mean that such computers possess no hardware connections at the CPU – memory bus level, but are connected by external interfaces that run under the control of software.<br /><br /><b>Parallel operating systems :-</b><br /><br />Parallel operating systems are used to interface multiple networked computers to complete tasks in parallel. The architecture of the software is often a UNIX-based platform, which allows it to coordinate distributed loads between multiple computers in a network. Parallel operating systems are able to use software to manage all of the different resources of the computers running in parallel, such as memory, caches, storage space, and processing power. Parallel operating systems also allow a user to directly interface with all of the computers in the network.<br /><br />A parallel operating system works by dividing sets of calculations into smaller parts and distributing them between the machines on a network. To facilitate communication between the processor cores and memory arrays, routing software has to either share its memory by assigning the same address space to all of the networked computers, or distribute its memory by assigning a different address space to each processing core. Sharing memory allows the operating system to run very quickly, but it is usually not as powerful. When using distributed shared memory, processors have access to both their own local memory and the memory of other processors; this distribution may slow the operating system, but it is often more flexible and efficient.</div>

Distributed Operating System & Parallel operating systems

Distributed Operating System:- It is a model where distributed applications are running on multiple computers linked by communications. A d...