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What's a "servo  embedded" feature

Posted on 2002-03-25
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Last Modified: 2010-04-26
What does it means a Hdd has a "servo embedded" feature ?

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Question by:hhheng
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jhance earned 200 total points
ID: 6893756
First, a "server" track on a disk is a special factory created track on the disk that is used by the controller on the drive to optimally calibrate the position of the HDA (R/W head assembly) over the data tracks on the disk.

It's essentially a "test pattern" that give a particular signal when the head is perfectly in place.

There are two ways of making servo tracks.  The oldest method is to dedicate an entire disk surface to this task.  This means that there is nothing on one entire surface of one of the platters in the disk other than servo tracks.  That means NO DATA.

Embedded servo track are interleaved with data tracks on one or more of the surfaces.  This has the advantage of permitting more data vs. servo information but it does make the manufacturing more complex.  There is also a danger of the R/W head erasing the servo data due to a problem in the drive.  Servo information CANNOT be re-created in the field even with a Low LEvel Format (LLF).  Only special factory equipment can re-do the servo tracks.

As a user of a disk drive, the presence of servo tracks is invisible and the only way you'll know they are there would be by reading marketing or technical documentation on the drive.
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Author Comment

by:hhheng
ID: 6893860
Thanks again, Mr know-all, ;>))
Cheers..
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LVL 32

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by:jhance
ID: 6893870
Is this an acceptable answer?

If so, you should accept it as an answer.

If not, please explain where additional information is needed.
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LVL 31

Expert Comment

by:rid
ID: 6893871
There are people around here, who propose really weak hypotheses (guesswork) as "answers". jhance has given you the opposite here.
Way to go
/RID
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LVL 32

Expert Comment

by:jhance
ID: 6893888
Well, many of the "experts" here learned their stuff from looking at web sites.  There are those of us who have actually been involved in the design and development of real disk drives.  In my case it was the development of microcode in a controller for a Seagate disk drive in the mid-80's.  I think it was a MASSIVE 20MB 5.25" unit.  (It seems like a dinosaur today but back then it was "cutting-edge".
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LVL 4

Expert Comment

by:1175089
ID: 6893940
Hey boys, you are so serious /like as Sam (Serious) Stown :-)), proposed answers, rejected answers, these bad gays (like me) with ther guesswork - don't worry, be happy, make love not war- is there anybody?!!!
And now some useful links:
http://www.storage.ibm.com/ipl/oem/tech/noid.htm
http://www.storage.ibm.com/hdd/technolo/truetrack.htm
Aberration, sorry...
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LVL 31

Expert Comment

by:rid
ID: 6894053
Serious? Sorry. It must be because it's that day of the week...
/RID
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Author Comment

by:hhheng
ID: 6894106
..sorry,Wrong click..Monday blues.
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Author Comment

by:hhheng
ID: 6894143
Thanks "1175089" for info on useful links.

Cheers to everybody.


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