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If you have the disk rotating at 360 rpm, then one byte is read off the disk in:

T = b/rN = 1/(360 rpm*512 bytes/sector * 96 sectors/track)

T = 3.4 μs

If one interrupt occurs every byte, then the operating system will process an interrupt (2.5 μs), then do some work, thenprocess another interrupt, etc. The time between interrupts is equal to the time it takes to read one byte. In other words, the disk will read one byte, theninterrupt the operating system, then read another byte. The operating system will only be able to get work done if it has enough time to finish processing aninterrupt before the next one occurs. In this case, the processor will spend 2.5 μs / 3.4 μs or 74% of its time handling I/O.

With DMA, there is only one interrupt for the entire sector. It takes 3.4 μs/byte * 512 bytes/sector = 1,741 μs to read the sector.Therefore the processor only spends 2.5 μs / 1741 μs = .14% of the time handling I/O.

Note: The above answer does not take into account rotational delay. If you include rotational delay, then the time to read a bytebecomes very large:

T = b/rN + 1/2r = 83 ms

This means the time the processor spends processing interrupts is very small (approximately .003% in both cases).

It should be clear that disk striping can improve the data transfer rate when the strip size is small compared to the i/o request size. it shouldAlso be clear that raid 0 provides improved performance relative to a single large disk, because multiple i/o requests can be handled in parallel. however,In this latter case, is disk striping necessary? that is, does disk striping improve i/o request rate performance compared to a comparable disk array withoutStriping?


Consider a disk array that does not use striping. If multiple I/O requests are issued for files on different disks, then performanceis the same as a striped disk array. However, the advantage of striping is that it improves the chances that multiple I/O requests will in fact be for data ondifferent disks. Without striping, all the files from a given directory will be on the same disk, so a single user operating in a single directory will be usingone disk instead of all the disks in the array. Likewise, it is likely that all user files will be on one disk, and all binaries on another, so that multipleusers accessing their files will use the same disk. Disk striping is a simple, automated way for the administrator of the array to ensure that files are spreadout across all the disks.

You purchase a disk drive that spins at 9600 rpm, stores 300 kb per track, and has an average seek time of 8 ms.

  • What is the average transfer time to read a 1 MB file, assuming the file is stored on consecutive tracks?

T = Ts + 1/(2r) + b/(rN)

T = .008 + (60 s/m)(1 r)/ (2*9600 r/m) + (1 MB)(1024 KB/MB)(60 s/m)/(9600 r/m)(300 KB/r)

T = .008 s + .003125 s + .021333 s

T = 32.458 ms

  • What is the average transfer time to read a 1 MB file, assumingthat the file is stored in 10 separate locations on the disk, and each location has 100 KB of contiguous data?

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Operating systems. OpenStax CNX. Aug 13, 2009 Download for free at http://cnx.org/content/col10785/1.2
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