Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!mit-eddie!bu-cs!purdue!decwrl!sun!imagen!atari!portal!cup.portal.com!Sullivan
From: Sullivan@cup.portal.com
Newsgroups: comp.sys.amiga.tech
Subject: Re: Request to Commodore (Bad Blocks)
Message-ID: <9514@cup.portal.com>
Date: 28 Sep 88 03:41:49 GMT
References: <6392@batcomputer.tn.cornell.edu> <1410009@hpcvca.HP.COM>
Distribution: na
Organization: The Portal System (TM)
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XPortal-User-Id: 1.1001.5165

> 
> >	No, we gave it up for at best a 33% increase in speed (for
> >writes: (1.5-1.0)/1.5 by your way of calculating, 50% (1.5-1.0/1.0)).
> 
> This is deceptive.  The uncoupled trackdisk.device is 33% faster than
> the (hypothetical) coupled trackdisk.device FOR WRITES ONLY.  For
> reads they are the same speed.  I contend that I read (about) 5 times
> as many tracks as I write.  Taking a weighted average gives 7% OVERALL.
> 
I think he was taking issue with your statement "at *BEST* a 7% increase..."
> 
> > Use disks without flaws.
> >	Sullivan Segall
> 
> How do you know a disk has no flaws?  Formatting does not tell you.
> The format program only puts data on parts of the track.  Other parts
> of the track can be flawed and will still pass Format/Verify.
> However, these flawed parts can still bite you on later track writes.
> That is because the data can be written anywhere on the track, not
> just on the originally formatted part.
> 
My experience with 3" floppies has been:
  Single sided disks have many flaws on their untested sides.
  Disks which commonly sell for less than $1.20 ea. have innumerable
    flaws on both sides (dual sided or not.)
  FUJI disks have no flaws (I haven't encountered a single error in
    the more than 200 fuji disks that I am now using, and have used
    for the past year and a half.  Mileage may vary.
  Kodak disks also give me no problems
  Sony, Precision, and Generic are the worst offenders of those I've 
    tried, listed from worst to best.

No company truly produces nothing but flawless disks, but there is sufficient
margin for error in the media that it really doesn't matter, as long as they
have high standards and reasonable levels of QA.  (In my experience about
3 in 10 Sony's were bad, 2 in 10 Precisions and 2 in 10 Generic, depending
on the batch, with an unusually large standard deviation.)

> ---------------------------------------------------------------------
> 
> All of the above numbers assume the current AmigaDos trackdisk.device
> which does not couple to the index pulse.  If you couple the
> trackdisk.device, the probability of a defect migrating into the data
> area after a successful Format/Verify goes to 0%.  What this buys me
> is confidence that a disk which has been Format/Verify'ed is in fact
> good.  Without the index coupling I can never have that confidence.
> 
> Charles Brown	charles%hpcvca@hplabs.hp.com

                           -Sullivan Segall
                            (still looking for a 68881 that
                             can be piggy-backed on a 68000)
_____________________________________________________________

/V\  My opinions are guaranteed to be worth at least what you
 '   paid for them.   If you are dissatisfied,  please return
     them to the nearest vendor for a full and prompt refund.
To Quote the immortal Socrates: "I drank what?" -Sullivan
_____________________________________________________________

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