b. How seek time, latency time, data transfer rate, and access time of magnetic disk is calculated? Explain in detail?
Answers
Answer:
Seek time is the time taken for a hard disk controller to locate a specific piece of stored data. Other delays include transfer time (data rate) and rotational delay (latency). When anything is read or written to a disc drive, the read/write head of the disc needs to move to the right position.
Explanation:
Answer:
Explanation:
Consider a disk pack with the following specifications- 16 surfaces, 128 tracks per surface, 256 sectors per track and 512 bytes per sector.
Answer the following questions-
What is the capacity of disk pack?
What is the number of bits required to address the sector?
If the format overhead is 32 bytes per sector, what is the formatted disk space?
If the format overhead is 64 bytes per sector, how much amount of memory is lost due to formatting?
If the diameter of innermost track is 21 cm, what is the maximum recording density?
If the diameter of innermost track is 21 cm with 2 KB/cm, what is the capacity of one track?
If the disk is rotating at 3600 RPM, what is the data transfer rate?
If the disk system has rotational speed of 3000 RPM, what is the average access time with a seek time of 11.5 msec?
Solution-
Given-
Number of surfaces = 16
Number of tracks per surface = 128
Number of sectors per track = 256
Number of bytes per sector = 512 bytes
Part-01: Capacity of Disk Pack-
Capacity of disk pack
= Total number of surfaces x Number of tracks per surface x Number of sectors per track x Number of bytes per sector
= 16 x 128 x 256 x 512 bytes
= 228 bytes
= 256 MB
Part-02: Number of Bits Required To Address Sector-
Total number of sectors
= Total number of surfaces x Number of tracks per surface x Number of sectors per track
= 16 x 128 x 256 sectors
= 219 sectors
Thus, Number of bits required to address the sector = 19 bits
Part-03: Formatted Disk Space-
Formatting overhead
= Total number of sectors x overhead per sector
= 219 x 32 bytes
= 219 x 25 bytes
= 224 bytes
= 16 MB
Now, Formatted disk space
= Total disk space – Formatting overhead
= 256 MB – 16 MB
= 240 MB
Part-04: Formatting Overhead-
Amount of memory lost due to formatting
= Formatting overhead
= Total number of sectors x Overhead per sector
= 219 x 64 bytes
= 219 x 26 bytes
= 225 bytes
= 32 MB
Part-05: Maximum Recording Density-
Storage capacity of a track
= Number of sectors per track x Number of bytes per sector
= 256 x 512 bytes
= 28 x 29 bytes
= 217 bytes
= 128 KB
Circumference of innermost track
= 2 x π x radius
= π x diameter
= 3.14 x 21 cm
= 65.94 cm
Now, Maximum recording density
= Recording density of innermost track
= Capacity of a track / Circumference of innermost track
= 128 KB / 65.94 cm
= 1.94 KB/cm
Part-06: Capacity Of Track-
Circumference of innermost track
= 2 x π x radius
= π x diameter
= 3.14 x 21 cm
= 65.94 cm
Capacity of a track
= Storage density of the innermost track x Circumference of the innermost track
= 2 KB/cm x 65.94 cm
= 131.88 KB
≅ 132 KB
Part-07: Data Transfer Rate-
Number of rotations in one second
= (3600 / 60) rotations/sec
= 60 rotations/sec
Now, Data transfer rate
= Number of heads x Capacity of one track x Number of rotations in one second
= 16 x (256 x 512 bytes) x 60
= 24 x 28 x 29 x 60 bytes/sec
= 60 x 221 bytes/sec
= 120 MBps
Part-08: Average Access Time-
Time taken for one full rotation
= (60 / 3000) sec
= (1 / 50) sec
= 0.02 sec
= 20 msec
Average rotational delay
= 1/2 x Time taken for one full rotation
= 1/2 x 20 msec
= 10 msec
Now, average access time
= Average seek time + Average rotational delay + Other factors
= 11.5 msec + 10 msec + 0
= 21.5 msec
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