Applied Grand Test 2

Question

Given a disk with 100 cylinders (0 to 99). Exactly one time unit is required to move the read/write head from one cylinder to the next. At time 0 the heads are at cylinder 0 and no requests are pending. The following six requests arrive at times shown below:

Time :       0 10 20 70 80 90

Cylinder : 21 75 16 68 2 17

Note that once heads are moving, arrival of new requests will not alter the intended destination of the heads in movement. Assuming, that rotational and transfer times are negligible, the total time required for the Scan algorithm is _____

Comments

intially head at 0^th cylinder  okkk

let go one by one 

at time  zero head at cylinder zero  and now coming cylinder  21 service it  till  21 time unit 75 and 16 also come but here scan algorithm service from one end to another end  so first it complete all service in its path till the end okk 

 tme unit 70 68 cylinder it aslo come  so the head not going in reverse order okk  so 68 not service it in its on going path 80 and 90 time unit  2  and 17 which back side of the head so head go on right side till the end and reverse its direction and service till last cylinder 2 

so overall  head movement 

(99-0)+(99-2)=196 

here in question mention onne head movement taken one unit time for one headmovement so ans is 196

okk

Answer 1

disk with 100 cylinders →  (0 to 99)

Initially we are at location 0

We have to use SCAN algorithm.