Another Example—Awaiting an Event
Task Issues Call to OS for Disk Read
The application program calls the OS requesting that a block of data be read from a disk drive into memory. Once a disk read request is forwarded to the disk interface, the disk read/write head mechanism must be positioned over the target disk cylinder. This is a lengthy mechanical process typically requiring milliseconds to complete. When the head mechanism has positioned the read/write heads over the target cylinder, the disk interface must then wait for the start sector of the requested block to be presented under the read head. The duration of this delay is defined by the rotational speed of the disk drive as well as the circumference of the cylinder. Once again, this ...
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