Date: Tue, 26 Nov 1996 14:40:05 +1030 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: joelh@gnu.ai.mit.edu (Joel Ray Holveck) Cc: msmith@atrad.adelaide.edu.au, terry@lambert.org, grog@lemis.de, chat@FreeBSD.org, smut@clem-162.dorms.tamu.edu Subject: Re: SCSI A/V drives Message-ID: <199611260410.OAA01379@genesis.atrad.adelaide.edu.au> In-Reply-To: <199611260403.XAA10823@hill.gnu.ai.mit.edu> from Joel Ray Holveck at "Nov 25, 96 11:03:52 pm"
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Joel Ray Holveck stands accused of saying: > > Okay, understood... I hadn't realized that the recal was a > > time-consuming process. Why does the drive logic not continuously > > update the thermal expansion factor it uses, each time it seeks? > Some do; it's an expensive process though, and often servo logic > doesn't have the grunt for it (think 'low cost'). > > Expensive in terms of time (and where is it spent? Calculations or > head seeks?) or in terms of circuitry or what? Time is the big issue. Compute time for the servo controller, and depending on design, possibly also dwell time for the head (some servos may sweep across the track in order to locate the precise centrepoint between guard tracks). > Is this type of logic usually handled by a controller with a PROM or > by custom circuitry? That varies between manufacturers. Seagate use a multiprocessor architecture with a 16-bit micro doing the bus and protocol stuff and an 8-bit micro running the servo. Quantum use a single micro and a couple of custom blobs on the drives of theirs I've seen. > Joel -- ]] Mike Smith, Software Engineer msmith@gsoft.com.au [[ ]] Genesis Software genesis@gsoft.com.au [[ ]] High-speed data acquisition and (GSM mobile) 0411-222-496 [[ ]] realtime instrument control. (ph) +61-8-8267-3493 [[ ]] Unix hardware collector. "Where are your PEZ?" The Tick [[
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