discuss different delays that occur in a storage system with conventional hard disk setup

Operating systems questions and answers, OS University exam questions, what are the different delays happen while accessing data in a hard disk

Question:

List and discuss different delays that occur while servicing a request in a storage system with conventional hard disk setup.

 

Answer:

Seek time: time to move read/write head from its current position to the desired track. It is the time taken for a hard disk controller to locate a specific piece of stored data. It may take 3 to 12 milliseconds (9ms is common for desktop drives).

Rotational latency: time for desired sector on target track to spin under the read/write head. May take 1-2 milliseconds (medium)

Transfer time: it is about how long the actual data read or write takes. Time to read the target sector and transfer bytes to host computer. The transfer time is the estimated time for the completion of a data transmission. A millisecond or less (low).

Wait time: time spent in I/O queue waiting for service. Could be 0 or more milliseconds, depending on number of requests queued and the disk request scheduling policy used.

 

******************

Related Questions:

 

• What needs to be saved and restored on a context switch between two threads in the same process?

• List down the benefits of per-process address space.

• Why the scheduling of processes and threads on a multi-processor system is more complicated than scheduling them on a uni-processor system.

• List and discuss different delays that occur while servicing a request in a storage system with conventional hard disk setup.

• Explain the purpose of system calls in an operating system with an example.

• What is a special file? Define block special file and character special file with examples. What is the essential difference between a block special file and a character file?
  

What is seek time

What is rotational latency

how does rotational latency affect the performance in a disk