Dr C.Naveeth Babu

  File A file is a named collection of related information that is recorded on secondary storage such as magnetic disks, magnetic tapes and optical disks. In general, a file is a sequence of bits, bytes, lines or records whose meaning is defined by the files creator and user. File Structure A File Structure should be according to a required format that the operating system can understand. A file has a certain defined structure according to its type. A text file is a sequence of characters organized into lines. A source file is a sequence of procedures and functions. An object file is a sequence of bytes organized into blocks that are understandable by the machine. When operating system defines different file structures, it also contains the code to support these file structure. Unix, MS-DOS support minimum number of file structure. File Type File type refers to the ability of the operating system to distinguish different types of file such as text files source files and binary files et

  As we know, a process needs two type of time, CPU time and IO time. For I/O, it requests the Operating system to access the disk. However, the operating system must be fare enough to satisfy each request and at the same time, operating system must maintain the efficiency and speed of process execution. The technique that operating system uses to determine the request which is to be satisfied next is called disk scheduling. Seek Time Seek time is the time taken in locating the disk arm to a specified track where the read/write request will be satisfied. Rotational Latency It is the time taken by the desired sector to rotate itself to the position from where it can access the R/W heads. Transfer Time It is the time taken to transfer the data. Disk Access Time Disk access time is given as, Disk Access Time = Rotational Latency + Seek Time + Transfer Time Disk Response Time It is the average of time spent by each request waiting for the IO operation. Purpose of Disk Scheduling The main p