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From: dbw@crash.cts.com (David B. Whiteman)
Newsgroups: comp.sys.mac
Subject: Re: What does 'ShutDown' do to Third Party SCSIs?
Message-ID: <2076@crash.cts.com>
Date: Thu, 3-Dec-87 05:02:53 EST
Article-I.D.: crash.2076
Posted: Thu Dec  3 05:02:53 1987
Date-Received: Mon, 7-Dec-87 06:40:49 EST
References: <4550@well.UUCP> <11540056@hpsmtc1.HP.COM>
Reply-To: dbw@crash.CTS.COM (David B. Whiteman)
Organization: Crash TS, El Cajon, CA
Lines: 16

Whether the "Shutdown" command from the Finder parks the heads on 3rd party
drives depends on the 3rd party.  From my experiments in trapping the SCSI
dispatch trap while shutting down, all the SCSI drivers that I have tested,
which is in noway representative of all drives, do not sent a shutdown
command to the drive.  The volume is flushed, ejected, and unmounted, but there
is no head seek to the innermost cylinder, nor is the Start/Stop SCSI command
issued.  I wrote a special head parking program which does send the Start/Stop
command on shut down.  When I use it I can actually hear the heads park on my 
drives.  According to Seagate's manual for my drive, which is a Seagate 225N,
the drive can withstand 40g's as opposed to 10g's if the heads are parked.
The Seagate 225N is used in some of Apple's HD20SC's, all of GCC FX20's, 
Jasmine 20's, MacMates Reflex 20 and none of these drivers parked heads
during shutdown from the Finder when I tested them about 7 months ago.  Of
course this may have changed with a software upgrade since then.  Most of the
larger drives park heads automatically when the power is turned off, so no
shut down command is actually needed in this case.