Device Management, Fault tolerance

Question 1

Formula for total time taken to read

Answer 1

Ta = Ts + 1/2r + b/rN
Ts= average seek time
r = rotational speed
b = bytes to be transferred
N = track size/bytes on track

Question 2

3 techniques performing I/O

Answer 2

1. programmed
2. interrupt-driven
3. direct memory access (DMA) - best efficiency, CPU involved at start and end of transfer

Question 3

Seek time
Rotational Delay

Answer 3

time taken for R/W head to position on right track
time taken for R/W head to position at start of right sector

Question 4

RAID levels & characteristics

Answer 4

0: performance, no duplicate/parity bits
1/mirror: duplicate data, need twice amount of disks
4: support one hard disk failure, occupy one hard disk for parity bits
5: support one hard disk failure, occupy one hard disk for spread out parity bits
6: support two hard disk failure
occupy two hard disk for spread out parity bits

Question 5

Differences in I/O device

Answer 5

data rate, application, complexity of control, unit of transfer, data representation, erorr condition