Disk Scheduling磁盘调度 The operating system is responsible for using hardware efficiently for the disk drives, this means hav ing a fast access time and disk bandwidth.操作系统有责任高效地使用硬件——对 于磁盘设备,这意味着很短的访问时间和磁盘带宽。 Access time has two major components访问时间包括两个主要 部分 Seek time is the time for the disk are to move the heads to the cylinder containing the desired sector..寻道时间是指把 磁头移到所需柱面的时间 Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head.旋转延迟是指 等待磁盘上所需要的扇区旋转到磁头下面的时间。 Minimize seek time最小寻道时间 Seek time≈ seek distance寻道时间≈寻道距离 Disk bandwidth is the total number of bytes transferred, div ided by the total time between the first request for serv ice and the completion of the last transfer.磁盘带宽,是用传输的总位数,除 以第一个服务请求与最后传输完成之间的总时间。 Applied Operating System Concepts 13.3 Silberschatz, Galvin, and Gagne @199913.3 Silberschatz, Galvin, and Gagne ©1999 Applied Operating System Concepts Disk Scheduling 磁盘调度 • The operating system is responsible for using hardware efficiently — for the disk drives, this means having a fast access time and disk bandwidth. 操作系统有责任高效地使用硬件——对 于磁盘设备，这意味着很短的访问时间和磁盘带宽。 • Access time has two major components 访问时间包括两个主要 部分 – Seek time is the time for the disk are to move the heads to the cylinder containing the desired sector. 寻道时间是指把 磁头移到所需柱面的时间。 – Rotational latency is the additional time waiting for the disk to rotate the desired sector to the disk head. 旋转延迟是指 等待磁盘上所需要的扇区旋转到磁头下面的时间。 • Minimize seek time 最小寻道时间 • Seek time  seek distance 寻道时间  寻道距离 • Disk bandwidth is the total number of bytes transferred, divided by the total time between the first request for service and the completion of the last transfer. 磁盘带宽，是用传输的总位数，除 以第一个服务请求与最后传输完成之间的总时间