Disk Head Scheduling

• method of ordering disk requests
  • based on cylinder number
  • moving the arm inwards and outwards along the disk surface is the slowest mechanical operation
• three parts:
  • seek time: time for head to move to appropriate track or cylinder
  • latency time: time for desired block to rotate under the read-write head
  • transfer time: time required to transfer data between disk and main memory
• try to do operations on nearby cylinders at about the same time
• disk requests can be reads or writes; can be used for swapping, paging, or file use