Path: utzoo!mnetor!uunet!cbmvax!hedley
From: hedley@cbmvax.UUCP (Hedley Davis)
Newsgroups: comp.sys.amiga
Subject: Re: Warm Reboot and Hard Disk Noise
Message-ID: <3718@cbmvax.UUCP>
Date: 3 May 88 16:33:19 GMT
References: <8804300422.AA18746@decwrl.dec.com> <12083@tut.cis.ohio-state.edu> <20570@sci.UUCP>
Reply-To: hedley@cbmvax.UUCP (Hedley Davis)
Organization: Commodore Technology, West Chester, PA
Lines: 41

In article <20570@sci.UUCP> raymund@sci.UUCP (Raymund Galvin) writes:
>In article <12083@tut.cis.ohio-state.edu>, erd@tut.cis.ohio-state.edu (Ethan R. Dicks) writes:
>< 
>< Your drive buzzes on warm start, (like mine too), because the controller 
>< forgets where the heads are when reset, and must get the heads back to a
>< known place.  Since on the Amiga, the most likely place for the heads to be is
>< over the root track,and most Amiga owners only have one BIG partition, that's 
>< a lotta tracks to cover when pulling the heads to the edge of the disk. The
>< noise you hear is as a result of either the hddisk.device stepping the tracks
>< very fast to 0, or a command sent to the drive itself, telling it to reset the
>< heads (I don't know which, because I don't know much about the hddisk.device)
>< 
>
>I doubt it. Two seconds of noise for a simple seek.  Give me a break.  
>These days many drives are rated as having average seek times in the 
>20-60 millisecond range.  An average seek for a drive translates to one 
>third of a full stroke seek.   The absolute worst case seek shouldn't be more 
>than 3 times the average seek time (usually it will be less).  I would 
>bet that whoever wrote the code that is messing around with the hard 
>disk (during reboots) is doing something silly.   I wish someone
>from Commodore would explain what is happening.
>
>Ray Galvin

How about this:

	The system boots, and the driver comes up and says 'Is the disk
at track zero ?'. The disk isn't, nor does the disk even know where it
s own head is. The veiw of the world here is a single bit which says
'Is the head over track zero ?'. Now, we could tell the disk to seek
a few hundred tracks over, but then  if the disk was on track 5 , it
would come rushing back towards track zero, and WHAM, hit the head stop
with incredible velocity. This would not be a good thing.

	So, the when the system boots, and the head is not over track
zero, it backs the head up ONE track and checks again. This takes
quite a while ( like a a couple of seconds ). Figure 20 ms seek time,
and 100 tracks would yeild 2 seconds of noise. Real numbers may vary,
but the general result is the same.

Hedley