A hard disk is made of a material with a linear coefficient of expansion of 1.5 × 10 ?6/°C. The track?to?track spacing is 1,000 nm. Assuming that the head is perfectly aligned over a track at a radius of 2 in. and that the error rate increases if the head strays 20% off track, how much temperature rise can we afford? What do you conclude from your answer?
What will be an ideal response?
We are going to assume that the expansion (movement) is in the disk for the sake of simplicity. If the tracks
are spaced by 1,000 nm than a 20% error in tracking corresponds to 200 nm. The head is 2 inches from the
center and thermal expansion must not move the track by more than 200 nm. If the disk heats up by one
degree, then the track moves by 2 × 1.5 × 10 ?6 = 3.0 × 10 ?6 inches. Since one inch is 25,400,000 nm, the
expansion is 3.0 × 10 ?6 × 2.54 × 107 = 76.2 nm/°C.
If the tolerance is 200 nm, the required change of temperature would be 200/76.2 = 2.6°C. This is a small
temperature change which implies that the temperature change in hard drives should be small, or there must
be a dynamic head tracking mechanism (which there is) to compensate for temperature changes.
You might also like to view...
The standards of creating, testing, and maintaining ____ software are much stricter than other software, for obvious reasons.
A. contextual B. encrypted C. safety-critical D. multiprocess
The increment operator increments the value of a pointer variable by twice the size of the memory to which it is pointing.
Answer the following statement true (T) or false (F)
All mobile browsers support the use of plug-ins.
Answer the following statement true (T) or false (F)
Which statement is true?
a) Programs should be written as collections of small functions. b) A function must be no longer than one page. c) The best engineered functions have many parameters and perform many distinct tasks. d) Every function must include an explicit return statement.