2.6k views

Consider a disk system with $100$ cylinders. The requests to access the cylinders occur in following sequence:

$4, 34, 10, 7, 19, 73, 2, 15, 6, 20$

Assuming that the head is currently at cylinder $50$, what is the time taken to satisfy all requests if it takes $1ms$ to move from one cylinder to adjacent one and shortest seek time first policy is used?

1. $95 \ ms$
2. $119 \ ms$
3. $233 \ ms$
4. $276 \ ms$

edited | 2.6k views

$=(50-34)+(34-20)+(20-19)+(19-15)+(15-10)+(10-7)+(7-6)+(6-4)+(4-2)+(73-2)$

$=16+14+1+4+5+3+1+2+2+71$
$=119 \ ms$

by Active (4.2k points)
edited
Here in case of Shortest seek time first we don't need to do lot of  substraction & addition in this type of questions. It seems like it is necessary to actually calculate  small differences ! It is better to just draw actual movement & Then do computation.

Here sequence is like

50->34->20->19->15->7->4->2->73

So we can calculate like (50-2) + (73-2) = 71+48 = 119.
by Boss (41.9k points)
0
50->34->20->19->15->7->4->2->73

So we can calculate like (50-2) + (73-2) = 71+48 = 119. what is reference for this trick and this is not working with other questions please someone confirm authenticity of this trick .
0
this trick always [email protected]
+1
Trick :P... it is just normal subtraction eg if u want to calculate 10 -> 2 and intermediate req is 5. you will do (10-5) + (5-2)= 10-5+5 -2  -> (10-2 ).