"Rob Morley" wrote in message
t...
In article , "half_pint"
says...

"Rob Morley" wrote in message
t...
In article , "half_pint"
says...
"Rob Morley" wrote in message
t...
snip
Let's try this using really basic concepts and small words, shall
we?

Imagine two hard drives - both single platter single-sided, same
rotational speed. One is 1GB, the other is 4GB. In order to get
4GB
in
the same space as 1GB, the larger drive has twice as many tracks,
and
each track holds twice as much data as a track on the 1GB drive.
Now
imagine that you want to read a file that occupies 3/4 track on
the
4GB
drive - this will occupy 1 1/2 tracks on the 1GB drive, so while
the
4GB
drive can read it in a single revolution, the 1GB drive will need
to
make up to two revolutions to read the same amount of data. So,
all
other things being equal (which they are not) the 4GB drive is up
to
twice as fast as the 1GB drive.

Are you with me so far?


Yes!! Now imagine a file which occupies 1 degree of the track
(on *my* drive) and it is 180%s away (%=degree here)
the disk has to spin 181%s to get the data, however on your
'faster' drive it only has to spin 180.5 degrees, wow!!!!!
thats a great improvement!!!!! your drive is 181/180.5 faster
than mine, that is 1.00277 or 0.277% (back to real percents now).
So you are a quarter of a percent faster than me!!
Big deal!!!!!!! you would never notice it!!!!

Are you still with me?

Indeed. Now take into account that the head of the 1GB drive in my
example has to move from one track to the next before it can read the
second track - by the time it gets there it might have missed the
start
of the data, in which case it would need another revolution before it
was read. This makes the 1GB drive a third of the speed of the 4GB
drive.
Now lets look at the combined effect of seek time and access time.
Assume an average seek time of 11 milliseconds for both disks.
For a 5400RPM drive one revolution takes 11 milliseconds. So for the
scenario in my example you have
for the 1GB disk: 11 + 11 + 11 + 11 = 44mS
for the 4GB disk: 11 + 11 = 22 mS
That's the worst-case scenario on an unfragmented disk. As you said,
the best-case scenario sees very little difference. So on average we
might expect the 4GB drive to have completed its read in 66% of the
time
that it takes the 1GB drive. Remember we're talking a 4x difference
in
arial density - the drives you were originally comparing were ISTR 5GB
per platter versus 60 GB per platter, which gives a difference in
linear
density of around 330%, while my example used 200%.

Now tell me that the small drive is as fast as the big one - show your
workings.

I will do that tomorrow when I have more time :O)

Still waiting ...

It will be ready to read by Thursday.