GATE CSE 1998 | Question: 17

Question

Calculate the total time required to read 35 sectors on a 2-sided floppy disk. Assume that each track has 8 sectors and the track-to-track step time is 8 milliseconds. The first sector to be read is sector 3 on track 10. Assume that the diskette is soft sectored and the controller has a 1-sector buffer. The diskette spins at 300 RPM and initially, the head is on track 10.

Comments

no its in syllabus

---

@Sachin Mittal 1

---

Significance of the Assumption

The statement “Assume that the diskette is soft-sectored and the controller has a 1-sector buffer” specifies the operational characteristics of the disk system and determines the timing model used for analysis.

1. Soft-sectored diskette :

   A soft-sectored disk does not possess physically embossed marks to indicate the beginning of each sector.  

   Instead, sector identifiers are magnetically recorded and must be detected by the disk controller.  

   Consequently, after every seek operation, the controller may require a finite waiting period until the desired sector identifier rotates under the read/write head.  

   This property introduces the possibility of rotational latency between successive reads.

2. Controller with a 1-sector buffer :

   The controller is capable of temporarily storing one complete sector of data, thereby permitting the overlap of data transfer with the reading of the subsequent sector.  

   When consecutive sectors are located on the same track, this buffering allows continuous sequential reading without incurring an additional rotational delay between sectors.

Answer 1

Given: The diskette spins at 300 RPM

Time to read 1 track =1/300 minute

=60/300 seconds 

=1/5 seconds

Time to read one sector =(1/8)*(1/5)=1/40 seconds

now given that 35 sectors and started from the sector 3 on track 10th

so the distribution of sector which we have to read  is  6,8,8,8,5 

which means first we read 6 sectors of 10^th track 

after that, we will read 8 sectors of 11^th track 

after that, we will read 8 sectors of 12^th track

after that, we will read 8 sectors of 13^th track

after that, we will read 5 sectors of 14^th track

Given: the track-to-track step time is 8 milliseconds

we have to read the data from the 5 track (that is 6,8,8,8,5). we have to change the track 4 times.

therefore the total time to move from one track to another for these five-track =4*8 milliseconds=32ms

and total time to read 35 sectors =35*(1/40)=35/40 seconds=35000/40 ms=875 ms

so total time=875+32=907 ms 

Comments

Why average latency is not cosidered?? As we have to first move to sector 3 on the track 10.

---

adeemajain I think, they have only mentioned that initial head is on track 10 ..They have not specify on which sector intial head is poiting so...we are assuming its on sector 3 ..from where we have to start….so no need to consider intial rotational latency

---

@Arjun Sir, @Bikram Sir , please help in this question.