Describes Disk architecture ,Latency time ,seek time,Sector slipping

1. Disk Scheduling

2. Hard Disk
It is attached to a computer by a set of wires an I/O bus.
1.Advanced Technology Attachment
2.serial ATA
3.Universal Serial Bus
4.Fibre channel
Data transfer carried out by Controller
1.Host Controller
2.Disk Controller
Transfer Rate:Rate at which data flow between drive and computer

3. Disk Structure

5. Important concepts
1.Read write header files just above each surface of platter.
2.Heads are attached to disk arm.
3.Platter logically divided into circular tracks,which are subdivided into sectors
4.set of track at one arm position makes up a cylinder
There might be 1000 of cylinders in disk drive.
5.Head crash:Disk head flies on extremely thin cushion of air,there is danger that
head will make contact with disk surface.It may damage magnetic surface.

6. Disk architecture animation
https://www.youtube.com/watch?v=f07mLQwt-AI

7. https://www.youtube.com/watch?v=wteUW2sL7bc

8. Seek TIme
Seek time is the time taken to locate the disk arm to a specified track where the data is
to be read or write.
milliseconds

9. Rotational Latency
Time necessary for desired sector to rotate to the disk head is called the rotational
latency.

10. Disk Formatting
1.Preparing disk for initial use
2.low level formatting :
Disk is divided into sectors.
Fills disk with special data structure for each sector.
Data structure consists of Data header,data area,Trailer.
Header and trailer consists of sector number and error correcting code.

11. Partition
Partition disk into one or more groups of cylinders.
Partitioning is the process of dividing the hard-disk into one or more regions
One partition can hold os executable files,another partition holds user files

12. Logical Formatting
This process places a file system on disk and allows an operating system to
store and retrieve files.
Cluster:collection of blocks.

13. Bad Blocks
Bad Block is an area of storing media that is no longer reliable for the storage of data
because it is completely damaged or corrupted.
Bad sector transaction
1.OS tries to read logical block 87
2.The controller calculates error correcting code and finds that the sector is bad.It
reports that findings to the OS.
3.The next time the system is rebooted,a special command is run to tell the controller to
replace bad sector with spare.
4.After that ,whenever the system requests logical block 87,the request is translated into
replacement sector’s address by the controller
Sector slipping is a technique used to deal with defective sectors in hard disk drives.

14. Thank You…
References:Operating system Concepts :Galvin
https://www.geeksforgeeks.org/
Wikipedia