Magnetic memory method free pdf download

It is a static entity made up of program statement while process is a dynamic entity. Program contains the instructions to be executed by processor. A program takes a space at single place in main memory and continues to stay there. A program does not perform any action by itself. Process States As a process executes, it changes state. The state of a process is defined as the current activity of the process.

Process can have one of the following five states at a time. Ready 2 The process is waiting to be assigned to a processor. Ready processes are waiting to have the processor allocated to them by the operating system so that they can run. Running 3 Process instructions are being executed i. The process that is currently being executed. PCB is the data structure used by the operating system.

Operating system groups all information that needs about particular process. PCB contains many pieces of information associated with a specific process which is described below. Pointer is used for maintaining the scheduling list. Process State 2 Process state may be new, ready, running, waiting and so on. Program Counter Program Counter indicates the address of the next instruction to be 3 executed for this process. CPU registers CPU registers include general purpose register, stack pointers, index 4 registers and accumulators etc.

Memory management information This information may include the value of base and limit registers, the 5 page tables, or the segment tables depending on the memory system used by the operating system. This information is useful for deallocating the memory when the process terminates. Accounting information This information includes the amount of CPU and real time used, 6 time limits, job or process numbers, account numbers etc.

The PCB serves as the repository for any information which can vary from process to process. By this technique, the hardware state can be restored so that the process can be scheduled to run again. Definition The process scheduling is the activity of the process manager that handles the removal of the running process from the CPU and the selection of another process on the basis of a particular strategy. Process scheduling is an essential part of a Multiprogramming operating system.

Such operating systems allow more than one process to be loaded into the executable memory at a time and loaded process shares the CPU using time multiplexing. Scheduling Queues Scheduling queues refers to queues of processes or devices. When the process enters into the system, then this process is put into a job queue. This queue consists of all processes in the system. The operating system also maintains other queues such as device queue. Each device has its own device queue. This figure shows the queuing diagram of process scheduling.

Processes waits in ready queue for allocating the CPU. Once the CPU is assigned to a process, then that process will execute. While executing the process, any one of the following events can occur. Two state process model refers to running and non-running states which are described below. Non-Running Processes that are not running are kept in queue, waiting for their turn to execute. Each entry in the queue is a pointer to a particular process.

Queue is implemented by using linked list. Use of dispatcher is as follows. When 2 a process is interrupted, that process is transferred in the waiting queue. If the process has completed or aborted, the process is discarded. In either case, the dispatcher then selects a process from the queue to execute.

Schedulers Schedulers are special system software which handles process scheduling in various ways. Their main task is to select the jobs to be submitted into the system and to decide which process to run. Long term scheduler determines which programs are admitted to the system for processing. Job scheduler selects processes from the queue and loads them into memory for execution. Process loads into the memory for CPU scheduling.

It also controls the degree of multiprogramming. If the degree of multiprogramming is stable, then the average rate of process creation must be equal to the average departure rate of processes leaving the system. On some systems, the long term scheduler may not be available or minimal. Time-sharing operating systems have no long term scheduler.

When process changes the state from new to ready, then there is use of long term scheduler. Main objective is increasing system performance in accordance with the chosen set of criteria. It is the change of ready state to running state of the process. CPU scheduler selects process among the processes that are ready to execute and allocates CPU to one of them. Short term scheduler also known as dispatcher, execute most frequently and makes the fine grained decision of which process to execute next.

Short term scheduler is faster than long term scheduler. Medium Term Scheduler Medium term scheduling is part of the swapping. It removes the processes from the memory. It reduces the degree of multiprogramming. The medium term scheduler is in-charge of handling the swapped out-processes.

Suspended processes cannot make any progress towards completion. In this condition, to remove the process from memory and make space for other process, the suspended process is moved to the secondary storage. This process is called swapping, and the process is said to be swapped out or rolled out. Swapping may be necessary to improve the process mix. It controls the degree of It provides lesser control multiprogramming over degree of It reduces the degree of 3 multiprogramming multiprogramming.

It is almost absent or It is also minimal in time It is a part of Time sharing 4 minimal in time sharing sharing system systems. A context switch is the mechanism to store and restore the state or context of a CPU in Process Control block so that a process execution can be resumed from the same point at a later time. Using this technique a context switcher enables multiple processes to share a single CPU. Context switching is an essential part of a multitasking operating system features. When the scheduler switches the CPU from executing one process to execute another, the context switcher saves the content of all processor registers for the process being removed from the CPU, in its process descriptor.

The context of a process is represented in the process control block of a process. Context switch time is pure overhead. Context switching can significantly affect performance as modern computers have a lot of general and status registers to be saved.

Content switching times are highly dependent on hardware support. Context switching Some hardware systems employ two or more sets of processor registers to reduce the amount of context switching time. When the process is switched, the following information is stored. Process with highest priority is to be executed first and so on. Process is preempted and other process executes for given time period. Dining Philosophers Problem The scenario involves five philosophers sitting at a round table with a bowl of food and five chopsticks.

Each chopstick sits between two adjacent philosophers. The philosophers are allowed to think and eat. Since two chopsticks are required for each philosopher to eat, and only five chopsticks exist at the table, no two adjacent philosophers may be eating at the same time. A scheduling problem arises as to who gets to eat at what time.

This problem is similar to the problem of scheduling processes that require a limited number of resources Problems The problem was designed to illustrate the challenges of avoiding deadlock, a system state in which no progress is possible.

This attempted solution fails because it allows the system to reach a deadlock state, in which no progress is possible. This is a state in which each philosopher has picked up the fork to the left, and is waiting for the fork to the right to become available. What is Thread? A thread is a flow of execution through the process code, with its own program counter, system registers and stack.

A thread is also called a light weight process. Threads provide a way to improve application performance through parallelism. Threads represent a software approach to improving performance of operating system by reducing the overhead thread is equivalent to a classical process.

Each thread belongs to exactly one process and no thread can exist outside a process. Each thread represents a separate flow of control.

Threads have been successfully used in implementing network servers and web server. They also provide a suitable foundation for parallel execution of applications on shared memory multiprocessors.

Following figure shows the working of the single and multithreaded processes. Process Thread Process is heavy weight or Thread is light weight taking lesser 1 resource intensive.

Process switching needs Thread switching does not need to 1 interaction with operating system. In multiple processing environments each process All threads can share same set of open 1 executes the same code but has its files, child processes. If one process is blocked then no While one thread is blocked and other process can execute until the waiting, second thread in the same task 1 first process is unblocked.

Multiple processes without using Multiple threaded processes use 1 threads use more resources. In multiple processes each process One thread can read, write or change 1 operates independently of the another thread's data. The thread library contains code for creating and destroying threads, for passing message and data between threads, for scheduling thread execution and for saving and restoring thread contexts.

The application begins with a single thread and begins running in that thread. Kernel Level Threads In this case, thread management done by the Kernel. There is no thread management code in the application area. Kernel threads are supported directly by the operating system. Any application can be programmed to be multithreaded. All of the threads within an application are supported within a single process. Scheduling by the Kernel is done on a thread basis. The Kernel performs thread creation, scheduling and management in Kernel space.

Kernel threads are generally slower to create and manage than the user threads. Some operating system provides a combined user level thread and Kernel level thread facility. Solaris is a good example of this combined approach. Many to Many Model In this model, many user level threads multiplexes to the Kernel thread of smaller or equal numbers. The number of Kernel threads may be specific to either a particular application or a particular machine.

Many to One Model Many to one model maps many user level threads to one Kernel level thread. Thread management is done in user space. In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Modern magnetic-memory technology requires all-electric control of perpendicular magnetization with low energy consumption. Instead, an out-of-plane SOT 15 could directly switch perpendicular magnetization. We observe a three-fold angular dependence in both the field-free switching and the current-induced out-of-plane effective field. Experiments involving a wide variety of SOT bilayers with low-symmetry point groups 16 , 17 at the interface may reveal further unconventional spin torques in the future.

The authors declare that the main data supporting the findings of this study are available within the Letter and its Supplementary Information. Extra data are available from the corresponding author upon reasonable request. Source data are provided with this paper. Miron, I. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection.

Nature , — Liu, L. Spin-torque switching with the giant spin Hall effect of tantalum. Science , — Manchon, A. Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems. Current-induced switching of perpendicularly magnetized magnetic layers using spin torque from the spin Hall effect. Article Google Scholar. Pai, C.

Spin transfer torque devices utilizing the giant spin Hall effect of tungsten. Lau, Y. Spin—orbit torque switching without an external field using interlayer exchange coupling. Large magnetoresistance at room temperature in ferromagnetic thin Film tunnel junctions. Butler, W. Spin-dependent tunneling conductance of Fe MgO Fe sandwiches.

B 63 , Yuasa, S. Parkin, S. Giant tunnelling magnetoresistance at room temperature with MgO tunnel barriers. Slonczewski, J. Current-driven excitation of magnetic multilayers. Ralph, D. Spin transfer torques. Miron, I. Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature , — Liu, L. Spin-torque switching with the giant spin Hall effect of tantalum.

Science , — Ryu, J. Current-induced spin—orbit torques for spintronic applications. Yu, G. Switching of perpendicular magnetization by spin—orbit torques in the absence of external magnetic fields. Manchon, A. Current-induced spin-orbit torques in ferromagnetic and antiferromagnetic systems.

Rahaman, S. Size-dependent switching properties of spin-orbit torque MRAM with manufacturing-friendly 8-inch wafer-level uniformity. IEEE J. Electron Devices Soc.

Google Scholar. Sato, N. Two-terminal spin—orbit torque magnetoresistive random access memory. Wang, M. Field-free switching of a perpendicular magnetic tunnel junction through the interplay of spin—orbit and spin-transfer torques.

Nguyen, M. Since an error of control data causes the HDD 1 to enter an inoperative state, it is necessary to ensure the security of the control data. If an error is included in data stored in the nonvolatile semiconductor memory 25 , it is possible to recover the fixed number of error bits by executing ECC processing. However, since there is a limit to the extent to which the recovery can be achieved by the ECC processing, it is desirable to rewrite error bits.

Thus, a flash memory is a typical example of the nonvolatile semiconductor memory 25 to which rewriting can be electrically made. The NOR flash memory is a memory to which writing can be made on a byte basis. On the other hand, the NAND flash memory is a memory to which writing can be made on a block basis. In this embodiment, both types of the flash memories can be used. In another case, besides them, a FeRAM which uses a ferroelectric thin film material as a storage element can be used as a nonvolatile semiconductor memory to which rewriting can be electrically made.

To be more specific, data is rewritten during a specified period of time that falls within a period of time starting from a start notification of write-data transfer processing, which is sent from the HDD 1 to the host 51 , until a command completion notification.

Since there is a very small possibility that the power of the host 51 may be interrupted during this specified period of time, it is possible to securely rewrite data. Which part of the period of time starting from the start notification until the completion notification is used as the specified period of time depends on the design. However, it is desirable to start the rewrite processing in response to the start notification of the write-data transfer processing.

As a result, if a command completion notification is transmitted upon completion of the rewrite processing, it is possible to suppress the delay in the transmission of the command completion notification. A description will be made with reference to a sequence diagram in FIG. The host 51 issues a write command to the HDD 1 S After the HDD 1 receives the write command, as soon as the HDD is ready to receive write data thereof, the HDD 1 transmits a write-data transfer processing start notification to the host 51 S In addition, after transmitting the write-data transfer processing start notification, the HDD 1 starts rewrite processing S 13 of rewriting to the nonvolatile semiconductor memory In parallel with the rewrite processing S 13 , the HDD 1 receives the write data from the host 51 S After the transfer of the write data ends, as soon as the write data is stored in a write buffer write cache is ON , or is written to the magnetic disk 11 write cache is OFF , the HDD 1 enters a state in which the HDD 1 can transmit a completion notification of this write command to the host If the rewrite processing S 13 is completed in this timing, the HDD 1 transmits the command completion notification to the host S On the other hand, if the rewrite processing S 13 is not completed, the HDD 1 delays the transmission of the command completion notification until the completion of the rewrite processing S Then, on completion of the rewrite processing S 13 , the HDD 1 transmits the command completion notification to the host In this way, the rewrite processing is performed on the nonvolatile semiconductor memory 25 during a period of time starting when the HDD 1 notifies the host 51 of the start of the write-data transfer processing until the command completion notification is returned to the host Therefore, there is a very low possibility that the power of the HDD 1 may be turned OFF during the rewrite processing.

Accordingly, it is possible to perform rewriting processing on the nonvolatile semiconductor memory 25 with the security of control data being ensured. Next, a detailed description will be made of processing in the HDD 1 , relating to rewriting to the nonvolatile semiconductor memory 25 with reference to FIGS. In FIG. A buffer and a correction table are reserved as a data area in the RAM At this time, error correction processing of data stored in the nonvolatile semiconductor memory 25 is performed by required ECC.

If an error is corrected, a correction table is formed in the RAM When a first write command is issued from the host 51 S 11 , the host interface manager receives it through the host interface Upon being ready to receive write data, the host interface manager transmits a write-data transfer start notification to the host 51 through the host interface S Moreover, the host interface manager makes a judgment as to whether or not the write command is the first write command after the POR processing.

If judging the write command to be the first write command, the host interface manager instructs the rewrite processing part to perform rewriting to the nonvolatile semiconductor memory By executing the rewrite processing S 13 in the timing when the first write command is executed, it is possible to reliably perform the error correction of the control data during the operation of the HDD 1 , and thereby to increase the security of data.

If it is judged that the write command is not the first write command, the rewrite processing is not executed. On receipt of the rewrite-processing instruction from the host interface manager , the rewrite processing part refers to the correction table stored in the RAM 24 so as to obtain information as to whether or not there are correction bits, and the correction location address thereof.

If error-correction processing is performed by the ECC processing part on any of the bits, the rewrite processing part starts the rewrite processing of rewriting to the nonvolatile semiconductor memory 25 S In parallel with the rewrite processing, the write data that has been transferred from the host 51 is stored in the buffer included in the RAM 24 through the host interface S As soon as the write data is stored in the buffer , the command execution manager instructs the drive interface to write the data to the magnetic disk If the write cache is in an ON state, in a stage where all write data has been stored in the buffer , the host interface manager judges that the rewrite processing to the nonvolatile semiconductor memory 25 has been completed.

On the completion of the rewrite processing, the rewrite processing part notifies the host interface manager of the completion. This course introduces you to the most powerful memory techniques on earth.

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