I/O Management and Disk Schedulingإدارة الإدخال والإخراج وجدولة القرص

Slide 5: machine readable — used to communicate with electronic equipment: disk drives, USB keys, sensors, controllers, actuators.

Slide 11: data may be transferred as a stream of bytes or characters (e.g., terminal I/O) or in larger blocks (e.g., disk I/O).

Slide 15 (Table 11.1): through processor — programmed I/O (no interrupts), interrupt-driven I/O (use of interrupts); direct I/O-to-memory transfer — DMA (use of interrupts); the "no interrupts" cell for direct transfer is empty.

Slide 18: DMA configurations — I/O bus: reduces the number of I/O interfaces in the DMA module. Slide 16: single bus — all modules share the same system bus. Slide 17: integrated DMA & I/O — direct path, substantially cuts the required bus cycles.

Slide 22: each layer relies on the next lower layer to perform more primitive functions and provides services to the next higher layer; changes in one layer should not require changes in other layers.

Slide 28: access time is the sum of seek time (position the head at the desired track) and rotational delay (beginning of the sector reaches the head); transfer time is the time taken to transfer the data.

Slide 32: last-in, first-out — good for transaction processing systems; the device is given to the most recent user so there should be little arm movement; possibility of starvation since a job may never regain the head of the line.

Slide 35: C-SCAN restricts scanning to one direction only; when the last track has been visited in one direction, the arm is returned to the opposite end of the disk and the scan begins again.

Slide 37: FSCAN — two subqueues; when a scan begins, all requests are in one queue, the other empty; all new requests are put into the other queue; service of new requests is deferred until all of the old requests have been processed.

FIFO (slide 30): 50→30 (20), →70 (40), →60 (10), →20 (40) = 110. SSTF (slide 33): 50→60 (10), →70 (10), →30 (40), →20 (10) = 70.