Hitachi IC25N040ATCS04-0 Specifications - Page 110

11.12 Seek Overlap The drive provides accurate seek time measurement method. The seek command is usually used to measure the device seek time by accumulating execution time for a number of seek commands. With typical implementation of the seek command, this measurement must include the device and host command overhead. To eliminate this overhead, the drive overlaps the seek command as described below. The first seek command completes before the actual seek operation is over. Then the device can receive the next seek command from the host. However, the actual seek operation for the next seek command starts right after completion of the actual seek operation for the first seek command. The execution of two seek commands overlaps excluding the actual seek operation. With this overlap, total elapsed time for a number of seek commands is the total accumulated time for the actual seek operation plus one pre and post overhead. When the number of seeks is large, this overhead can be ignored. (1) With overlap Host process Device process Seek operation Overhead A Total time = (n-1) * (Seek operation) + A + B (2) Without overlap Host process Device process Seek operation Overhead A B+A Total time = n * (Seek operation + A + B) B B+A B Figure 70. Seek overlap Hitachi Travelstar 60GH & 40GN hard disk drive specifications 97