Unformatted text preview: • I t needs to know which components are busy and which are free The fi rst problem can be solved by f lagging each of states ( channel , control unit and device) Every single one receive bit that represents if the device is busy or free. T his f lag made up of three bits is located in main memory and its called Channel S tatus Word (CSW) Polling is one solution to test the f lag. The interrupts is more efficient way to test the f lag. • i t must be able to accommodate the requests that come in during heavy I /O t raffic; To solve this problem there is many of different algorithm such as FCFS fi rst-come f i rst served is the simples device-scheduling algorithm., (SSTF) Shortest seek time f i rst it used the same philosophy as Shortest Job next that we learned in chapter 4. A nother solution is SCAN also sometimes known as the elevator algorithm, in which t he arm doesn’t necessarily go to the edge unless there are requests. The C-Scan is a C ircular SCAN the arm picks up requests on i ts path during the inward. • I t must accommodate the dispari ty of speeds between the CPU and the I /O devices. This problem is solved by RAID Redundant Array of Inexpensive Disks. Because of t he RAID we can accommodate the gap between super fast CPU and slower I/O devices. There are seven primary levels of RAID. So buffering is the solution and i t’s really a great idea in all kinds of computers and electronic devices. ...
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This note was uploaded on 04/19/2011 for the course CS 250 taught by Professor Idontknow during the Spring '11 term at City College of San Francisco.
- Spring '11