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blog

A blog is your easy-to-use web site, where you can quickly post thoughts,interact with people, and more.

I am here to create some interesting and astonishing history of all time.

friends site

first
and
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log to this

The easiest thing in life is to earn a lot through blogging.

Payperpost

Now i think i have got a new exposure in the area of blogging. I think it will be a great experience in reserving the opportunities and earning money through that... payperpost is new, at least new to me, and I think it will be an interesting way to expand my knowledge on various subjects.

The premise is very simple: I can search through topics, do some research and write a post similar to this one detailing what the subject/service/business has to offer. Don’t get me wrong, I’m not going to retire with what I get for doing this, but it will help out.

The money I make from PPP will more than likely go towards keeping this site up and running. I like having a platform allowing people to talk about relevant subjects, but the site does not run on its own. PPP will hopefully cover the monthly costs – a good thing for all of us.

I heard about PPP while browsing looking for basically nothing. I have found some of the most interesting things just looking around and this is another one of those times.

One of the most surprising things about different sites on the internet is the people available to meet and network with. Facebook, Twitter, Pownce, Friendfeed and now PPP are all places where you can meet people in all walks of life and I look forward to getting to know some people in the PPP community.

TLB and arm stickness

In a cached system, the base addresses of the last few referenced pages is maintained in registers called the TLB that aids in faster lookup. TLB contains those page-table entries that have been most recently used. Normally, each virtual memory reference causes 2 physical memory accesses-- one to fetch appropriate page-table entry, and one to fetch the desired data. Using TLB in-between, this is reduced to just one physical memory access in cases of TLB-hit.

If one or a few processes have a high access rate to data on one track of a storage disk, then they may monopolize the device by repeated requests to that track. This generally happens with most common device scheduling algorithms (LIFO, SSTF, C-SCAN, etc). High-density multisurface disks are more likely to be affected by this than low density ones.

Buddy system of memory allocation

Good name na???:)Free memory is maintained in linked lists, each of equal sized blocks. Any such block is of size 2^k. When some memory is required by a process, the block size of next higher order is chosen, and broken into two. Note that the two such pieces differ in address only in their kth bit. Such pieces are called buddies. When any used block is freed, the OS checks to see if its buddy is also free. If so, it is rejoined, and put into the original free-block linked-list.This is an easy topic and can be read within two or three hours.It took just one hour for me to finish this topic.

demand- and pre-paging,placement and replacement algorithms,latency, transfer and seek time with respect to disk I/O:

Pretty long topic na.But the explanations of them are really simple.With demand paging, a page is brought into memory only when a location on that page is actually referenced during execution. With pre-paging, pages other than the one demanded by a page fault are brought in. The selection of such pages is done based on common access patterns, especially for secondary memory devices.
Placement algorithms determine where in available real-memory to load a program. Common methods are first-fit, next-fit, best-fit. Replacement algorithms are used when memory is full, and one process (or part of a process) needs to be swapped out to accommodate a new program. The replacement algorithm determines which are the partitions to be swapped out.

Seek time is the time required to move the disk arm to the required track. Rotational delay or latency is the time it takes for the beginning of the required sector to reach the head. Sum of seek time (if any) and latency is the access time. Time taken to actually transfer a span of data is transfer time.

concept of binary semaphore,thrashing,turnaround time and response time:

A binary semaphore is one, which takes only 0 and 1 as values. They are used to implement mutual exclusion and synchronize concurrent processes.
Thrashing is a phenomenon in virtual memory schemes when the processor spends most of its time swapping pages, rather than executing instructions. This is due to an inordinate number of page faults.

Turnaround time is the interval between the submission of a job and its completion. Response time is the interval between submission of a request, and the first response to that request.

Time stamping and cycle stealing:

It is a technique proposed by Lamport, used to order events in a distributed system without the use of clocks. This scheme is intended to order events consisting of the transmission of messages. Each system 'i' in the network maintains a counter Ci. Every time a system transmits a message, it increments its counter by 1 and attaches the time-stamp Ti to the message. When a message is received, the receiving system 'j' sets its counter Cj to 1 more than the maximum of its current value and the incoming time-stamp Ti. At each site, the ordering of messages is determined by the following rules: For messages x from site i and y from site j, x precedes y if one of the following conditions holds....(a) if Ti
We encounter cycle stealing in the context of Direct Memory Access (DMA). Either the DMA controller can use the data bus when the CPU does not need it, or it may force the CPU to temporarily suspend operation. The latter technique is called cycle stealing. Note that cycle stealing can be done only at specific break points in an instruction cycle.

Popular multiprocessor thread-scheduling strategies.

Gang Scheduling: A set of related threads is scheduled to run on a set of processors at the same time, on a 1-to-1 basis. Closely related threads / processes may be scheduled this way to reduce synchronization blocking, and minimize process switching. Group scheduling predated this strategy.
Dedicated processor assignment: Provides implicit scheduling defined by assignment of threads to processors. For the duration of program execution, each program is allocated a set of processors equal in number to the number of threads in the program. Processors are chosen from the available pool.
Dynamic scheduling: The number of thread in a program can be altered during the course of execution.

A must know concept

Scheduling is the process of allocating the CPU a process.Only one process can be executed at a time.They are of three types short-, long- and medium-term scheduling
Long term scheduler determines which programs are admitted to the system for processing. It controls the degree of multiprogramming. Once admitted, a job becomes a process.
Medium term scheduling is part of the swapping function. This relates to processes that are in a blocked or suspended state. They are swapped out of real-memory until they are ready to execute. The swapping-in decision is based on memory-management criteria.
Short term scheduler, also know as a dispatcher executes most frequently, and makes the finest-grained decision of which process should execute next. This scheduler is invoked whenever an event occurs. It may lead to interruption of one process by preemption.

Belady's Anomaly

One important and nice topic in Os that most people like is that of Belady's Anomaly.Also called FIFO anomaly. Usually, on increasing the number of frames allocated to a process' virtual memory, the process execution is faster, because fewer page faults occur. Sometimes, the reverse happens, i.e., the execution time increases even when more frames are allocated to the process. This is Belady's Anomaly. This is true for certain page reference patterns.It is a must for everyone learning OS to know about it.So learn it as soon as possible friends.

Dead lock:The easiest concept in operating system

It is a concept which tells about an error condition.Here the system is deadlocked and no process executes.i Will List the Coffman's conditions that lead to a deadlock.
*Mutual Exclusion: Only one process may use a critical resource at a time.
*Hold & Wait: A process may be allocated some resources while waiting for others.
*No Pre-emption: No resource can be forcible removed from a process holding it.
*Circular Wait: A closed chain of processes exist such that each process holds at least one resource needed by another process in the chain.
Deadlocks can be avoided and also prevented.

Some concepts:reentrancy

I am going to explain some key concepts in operating systems.Let us start with reentrancy.
It is a useful, memory-saving technique for multiprogrammed timesharing systems. A Reentrant Procedure is one in which multiple users can share a single copy of a program during the same period. Reentrancy has 2 key aspects: The program code cannot modify itself, and the local data for each user process must be stored separately. Thus, the permanent part is the code, and the temporary part is the pointer back to the calling program and local variables used by that program. Each execution instance is called activation. It executes the code in the permanent part, but has its own copy of local variables/parameters. The temporary part associated with each activation is the activation record. Generally, the activation record is kept on the stack.
Note: A reentrant procedure can be interrupted and called by an interrupting program, and still execute correctly on returning to the procedure.

Concepts in operating systems

Friends I like operating systems very much.I have studied every page and corner in the subject.It is a very interesting subject and it must be thoroughly read by the various students studying operating systems.It was a compulsory subject to me during my second year in Engineering.I even had a lab in it.We used a book which had a Dinosaur picture in the front(i couldn't find out what similarity that the author found between a dino and operating system).It had a red cover.The author was Abraham Silberschatz.He explained all the concepts of Operating systems very clearly and in an enjoyable manner.So friends try to use that book as much as possible.

Operating system

One of my favorite subject in my engineering studies was operating system. Do not know why im more crazy about that subject. Let me discuss about the concept that i learnt.. And will soon gather more info about this and will share in my later posts..