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From: cambpellster.john@gmail.com on 2 Jan 2006 16:19
I am trying to find the average seek time of the following
single-platter disk. I know that the seek time is 1ms for every 100
tracks traversed. The total number of tracks on one side of the platter
is 30,000. Then what is the average seek time?
I think it is: 1ms/100 .... it makes sense, right?

From: Anne & Lynn Wheeler on 2 Jan 2006 16:52
"cambpellster.john(a)gmail.com" <cambpellster.john(a)gmail.com> writes:
> I am trying to find the average seek time of the following
> single-platter disk. I know that the seek time is 1ms for every 100
> tracks traversed. The total number of tracks on one side of the platter
> is 30,000. Then what is the average seek time?
> I think it is: 1ms/100 .... it makes sense, right?

you need to take the avg. of all the seek distances. many times the
avg. seek distance is taken as half the maximum seek distance. given
that you know the avg. seek distance, then you can calculate the
avg. seek time (based on the avg. seek distance).

many disks have situation where it takes longer per track for short
seek distances than for long seek distances (having at least to do
with startup inertia and acceleration of the arm from rest).

there was once a couple high-school kids visiting this dam late at
night (for the first time) ... and the driver turned onto the highway
across the top of the dam and floored the gas pedal ... attempting to
see peak speed across the top. as they were coming to the other end of
the dam, one of the passengers mentioned that the driver should slow
down ... and the driver said there was no problem that they would just
coast thru the upcoming tunnel.

turns out that it wasn't a tunnel ... it was a garage where they
parked a large crane ... with a solid concrete wall in the back. they
barely avoided an extremely distructive instantaneous deaccleration
what was the avg. speed across the top of the dam?

--
Anne & Lynn Wheeler | http://www.garlic.com/~lynn/
From: Stephen Fuld on 2 Jan 2006 20:33

"Anne & Lynn Wheeler" <lynn(a)garlic.com> wrote in message
news:m3oe2ue1qu.fsf(a)lhwlinux.garlic.com...
> "cambpellster.john(a)gmail.com" <cambpellster.john(a)gmail.com> writes:
>> I am trying to find the average seek time of the following
>> single-platter disk. I know that the seek time is 1ms for every 100
>> tracks traversed. The total number of tracks on one side of the platter
>> is 30,000. Then what is the average seek time?
>> I think it is: 1ms/100 .... it makes sense, right?
>
> you need to take the avg. of all the seek distances. many times the
> avg. seek distance is taken as half the maximum seek distance.

The average of all the seek distances is the number of cylinders / 3, not
half the max. But note that this is misleading for modern disks with zone
bit recording, as there are more "addresses" to seek to on the outer
cylinders than on the inner ones, so the effective average is less.

--
- Stephen Fuld
e-mail address disguised to prevent spam


From: Bob on 2 Jan 2006 22:05
Stephen Fuld wrote:
> "Anne & Lynn Wheeler" <lynn(a)garlic.com> wrote in message
> > you need to take the avg. of all the seek distances. many times the
> > avg. seek distance is taken as half the maximum seek distance.
>
> The average of all the seek distances is the number of cylinders / 3, not
> half the max.

Doesn't this assume the disk is full? It also assumes that
disk accesses are random, which is far from true in most
real systems. Files that are written close together tend to
be read close together.

From: Skybuck Flying on 2 Jan 2006 23:41
Tell me about it.

I can't figure out if the SCSI harddisks are faster than the current SATA
harddisks.

First they say see seek time is 2 ms... than 8 ms... etc

I don't know...

It depends on the formula used to calculate all those figures.

And finally even that can be incorrect.

Best is probably to simply stick to the benchmark results.

It's kinda amazing to see the SATA harddisks of today out perform the SCSI
harddisks of the past... at least according to the benchmarks number of
input output operations.

Finally the SATA harddisk are like 3 to 4 times as big ;) and three times
cheaper as well ?! <- If that don't make you go holyshit then I dont know
what will ;)

Bye,
Skybuck.

<cambpellster.john(a)gmail.com> wrote in message
news:1136236770.968146.222870(a)f14g2000cwb.googlegroups.com...
> I am trying to find the average seek time of the following
> single-platter disk. I know that the seek time is 1ms for every 100
> tracks traversed. The total number of tracks on one side of the platter
> is 30,000. Then what is the average seek time?
> I think it is: 1ms/100 .... it makes sense, right?
>


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