LOOK Scheduling

• As we described them, both SCAN and C-SCAN move the disk arm across the full width of the disk.
• In practice, neither algorithm is often implemented this way. More commonly, the arm goes only as far as the final request in each direction.
• Then, it reverses direction immediately, without going all the way to the end of the disk.
• Versions of SCAN and C-SCAN that follow this pattern are called LOOK and C-LOOK scheduling, because they look for a request before continuing to move in a given direction (see Fig. 12.12).

  Figure 12.12: C-LOOK disk scheduling.