13.1 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

Quiz

a. Why is LOOK better than SCAN?

Answer the following two questions using exactly one of the words FCFS, SSTF, SCAN, LOOK, C-SCAN, C-LOOK

b. Which algorithm possibly results in starvation? c. Which of SCAN or C-SCAN gives better

throughput?

13.2 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

Where is RAID, or is SSTF implemented?

OS* … disk cheap … expensive older … newer serial … parallel (offload work and complexity) logical … physical

volume: logical disk; may span physical disks, or may have several volumes on a physical disk

OS must keep track of physical disks to do * above. Third alternative in middle is possible: OS … controller card (host bus-adapter) … disk

Operating System Concepts with Java – 7th Edition, Nov 15, 2006 Silberschatz, Galvin and Gagne ©2007

Excerpt from Chapter 13

13.4 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

How Does Plug and Play (PnP) work?

Reassigns port and maskable interrupt to avoid collision with another device.

Port: device register mapped to small amount of memory to provide control information.

(Contrast: Memory-mapped device, where large amount of memory provides data to or from the hardware.)

MIRQ and NMIRQ wires provide interrupt number, telling what interrupt occurred, provided by the CPU.

(Contrast: Interrupt level, which is a priority set by OS.)

13.5 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

Device I/O Port Locations on PCs (partial)

13.6 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

Pentium maskable vs. non-maskable interrupts

13.7 Silberschatz, Galvin and Gagne ©2007Operating System Concepts with Java – 7th Edition, Nov 15, 2006

Windows XP Interrupt Request Levels