The summary of lessons learned



Please write a two-page summary of the key lessons learned or “take-ways” from the reading assignments and discussions. The summary of lessons learned is not meant to be a regurgitation of the readings or discussions. Rather, it is meant to identify new concepts the student may have learned, a different perspective on a known concept, a reflection on the readings or discussions, or the application of concepts to the student's work environment.

Grading Rubric for Weekly Lessons Learned

In human readable for communication can be done with computer user. Where in machine readable the communication can be occur with electronic devices. On the software a device there is an influence in the operating system. Suppose a terminal may be an ordinary user the different privilege levels in operating system. As computer system has evolved, there is a pattern of complexity. The processor can be directly control with peripheral devices. With the specialized instruction set the I/O module is enhanced. The CPU directs the I/O processor to execute in the memory. Without processor intervention the I/O processor executes the instruction. With the direct memory access the all control of main memory id referred to an I/O channel. By integrating we can substantially require the I/O functions. The DMA logic may separate module that controls the several I/O modules. The bus system shares with the processor and the main memory is used by the Direct Memory Access to exchange data with memory.

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The I/O devices are slow compared with the main memory and the processor. For improving the efficiency of the I/O device the effort in I/O designs. The interests of simplicity desirable to handle all the devices are in a uniform manner. Here in the logical I/O deals with the device as the resources with the details of controlling the device. The request operations and data are converted into appropriate sequences of I/O instructions, channel commands and controller orders. For a communication device the I/O structure looks much the same as that just described in the logical I/O communication architecture which consist number of layers. In the directory management the file names are converted to identifiers that either reference the file directly. This layer also concerned with user operations which affect the directory of files. The file system layer deals with the logical structure of files and with operations those can be specified by the user. The physical organization must be converted in to physical main memory address segmentation and paging structure.


As the other areas of computer performance, while one of the component can only be pushed so far, disk storage designers recognize. In the case of disk storage, this leads to the development of arrays of disk that operate independently and in parallel. With multiple disks, separate I/O request can be handled in parallel, as long as the data required.

As a single logical drive RAID is a set of physical disk drives viewed by the operating system. Data are disturbed across the physical drives of an array. Redundant disk which guarantees data recoverability in case of a disk failure capacity is used to store parity information.

In the RAID we have several levels. Those are explained below:

In striping the data availability is lower than single disk. It's having very large I/O data transfer capacity. The small I/O request rate was very high for both read and write. In mirroring the data availability is higher than RAID 2, 3, 4 or 5 and lower than RAID 6. It's having the higher than single disk for read, similar to single disk for write. The small I/O request rate up to twice that of a single disk for read, similar to single disk for write. The performance of the RAID levels depends on the host system and the layout of the data. Several design of an I/O request is satisfied from the disk cache which the data in the disk must be delivered to process. The Least frequently used block in the ser has experiences the references. LFU makes the use of pertinent information because of it might seem the more appropriate. If one cache misses, a new block is in to the new section with the count one. In the new section the count remains at one as long as the block. With its count at one the block ages out of the new section. The buffer cache in UNIX is essentially I/O operations with disk are handled through the buffer cache. The data transfer between the buffer and the user process space always occur using DMA. The UNIX devices are disk drives, tape drives, terminals, communication lines, printers.

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Windows offers two modes of I/O operation. They are asynchronous and synchronous mode is used to optimize application performance. Asynchronous I/O is the more efficient compared to the synchronous mode. In this it allows to continue the execution while the I/O operations are managed by the I/O deceives. The thread that invoked the I/O operation can continue to execute until it reaches the completion of operations.

Files and File Systems: The most important part of the operating system is the user's point of view in the file system. With the secondary storage the file system provide the resources which can associate with the storage device. The files are stored on disk when the user logs off comes under the long term existence. Where the names of files can have associated with the permit controlled sharing can comes under the sharable between processes. In this we can create, delete, open, close, read, write all these performance can be done. The file structure contains the fields, records, file, and database. The file system software architecture can have each user should can perform all the file operations. Other user's files access controlled by each and every user. Another way of viewing the functions of a file system to interact with files for creating and deleting the file from server. The application of the priority will depend on the usage of file. The implementation can be conflict for economy of storage in the data. Most structure in one of these categories used in actual survey with a combination of these organization. The records are logical unit of a structured with secondary storage blocks. The I/O buffer allocation in the main memory is the organization of blocks on the secondary storage device. As opposed to a file that is treated only as a stream of bytes such as UNIX file system. The record blocking may interact with the virtual memory to make the page the basic unit of transfer. The pages are generally small so that some systems combine multiple pages to create a large block for the file I/O.