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  1. Department of Information Technology Subject Code:CS3451 Subject Tittle: Itroduction To Operating System Team Members: Reg No: Maju mon 210621205031 Manoj M 210621205032 Manoj P 210621205033 Mariam Jerina S 210621205034 Niranchan P 210621205035
  3. INTRODUCTION: • Disk Structure in Operating System: The actual physical details of a modern hard disk may be quite complicated. Simply, there are one or more surfaces, each of which contains several tracks, each of which is divided into sectors. There is one read/write head for every surface of the disk.
  4. DEFFINITION: • Modern disk drives are addressed as large one- dimensional arrays of logical blocks, where the logical block is the smallest unit of transfer. The size of a logical block is usually 512 bytes, although some disks can be low-level formatted to have a different logical block size, such as 1,024 bytes. This option is described in Section 12.5.1.
  5. • The disk is dividedinto tracks. • Each track is further dividedinto sectors. • The point to be noted here is that outer tracks are bigger in size than the inner tracks but they containthe same number of sectors and have equal storage capacity. • This is because the storage density is high in sectors of the inner tracks whereas the bits are sparsely arranged in sectors of the outer tracks. • Some space of every sector is used for formatting. • the actualcapacity of a sector is less than the given capacity.
  6. • Read-Write(R-W) head moves over the rotatinghard disk. • It is this Read-Write head that performs all the read and writes operationson the disk • hence, the position of the R-W head is a major concern. • To perform a read or write operationon a memory location,we need to place the R-W head over that position.
  7. • Seek time – The time taken by the R-W head to reach the desired track from its current position. • Rotational latency – Time is taken by the sector to come under the R- W head. • Data transfer time – Time is taken to transfer the required amount of data. It depends upon the rotational speed. • Controller time – The processing time taken by the controller. • Average Access time – seek time + Average Rotational latency + data transfer time + controller time.
  8. • What Is The Function OF Disks? • Magnetic disks can be used to store a wide range of data, including operating systems, software, and other files. Hard disk drives, in other words, can read and write data on hard disks. There is an HDD for each computer, which can be used as a primary or secondary storage device.
  9. • Advantages – 1.First Come First Serve algorithm has a very simple logic, it executes the process requests one by one in the sequence they arrive. 2.Thus, First Come First Serve is very simple and easy to understand and implement. 3.In FCFS eventually, each and every process gets a chance to execute, so no starvation occur.
  10. • Disadvantages – 1.This scheduling algorithm is nonpreemptive, which means the process can’t be stopped in middle of execution and will run it’s full course. 2.The throughput of FCFS is not very efficient. 3.FCFS is implemented on small systems only where input-output efficiency is not of utmost importance.