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From: ntaib@silver.ucs.indiana.edu (Nur Iskandar Taib)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: What is difference between Unformatted and Formatted HD capacity?
Message-ID: <1991Apr9.162212.22967@bronze.ucs.indiana.edu>
Date: 9 Apr 91 16:22:12 GMT
References: <1991Apr4.203413.7550@news.larc.nasa.gov> <5994@trantor.harris-atd.com>
Sender: news@bronze.ucs.indiana.edu (USENET News System)
Organization: Indiana University, Bloomington
Lines: 22

>	I have seen some drives having voice coil head positioning
>mechanisms that have an odd number of heads. But certainly all drives
>have an even number of platter surfaces. Is the missing head's
>platter and its bytes counted as part of the "Unformatted Capacity"?


The odd head is used for feedback for the head servo 
mechanism. That disk surface carries tracks that the 
head can follow. This allows very precise positioning 
and narrower tracks. 

This, incidentally, is the same technology used on 
those ultra-high capacity floppy drives (not the new
2.88 Meg ones, the older Kodak/Verbatim and Barnowl-li
units).

--
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Iskandar Taib                        | The only thing worse than Peach ala
Internet: NTAIB@AQUA.UCS.INDIANA.EDU |    Frog is Frog ala Peach
Bitnet:   NTAIB@IUBACS               !
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