Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!oliveb!sun!pepper!cmcmanis
From: cmcmanis%pepper@Sun.COM (Chuck McManis)
Newsgroups: comp.sys.atari.st
Subject: Re: SS disks
Message-ID: <50424@sun.uucp>
Date: 21 Apr 88 22:56:32 GMT
References: <184chad@byuvax.bitnet>
Sender: news@sun.uucp
Reply-To: cmcmanis@sun.UUCP (Chuck McManis)
Organization: Sun Microsystems, Mountain View
Lines: 50

In article <184chad@byuvax.bitnet> chad@byuvax.bitnet writes:
>Question: Is it true that MACs use the top of the disk while Atari/IBM
>use the undersides? 

No. Both use the same side. Sometimes bogus disk salespersons will lie
to you and say that DSDD disks and SSDD disks are exactly the same to
make a sale but they aren't. The disk manufacturing process goes something 
like this :
(I toured Dysan/Xidex once ...)
    o 	A sheet of mylar is coated on both sides with their own
	custom oxide.
    o	It is cut into little circles. 
    o	The circles are buffed to near flat on *one* side.
    o 	Disks are tested for R/W errors, ones that fail are recycled
    o   Some of the ones that pass get packaged as SS disks.
    o   The rest get burnished on the *other* side and tested again.
    o 	The ones that fail get recycled (humans can't tell which side
	failed) The ones that pass become DSDD disks.
	
>That is what I have heard.  If it is true, then it is the biggest scam
>around.

There *is* oxide on both sides of the disk and they are processed to be
DSDD disks, even though some get pulled early in the process. The problem
is that on 3.5" disks, where one is storing 135 Tracks/Inch, it is a *lot*
easier to get defects. (As opposed to 5.25" disks at 40 TPI). What does it
mean to you? It means
	1) Some percentage of that disks you buy that are labeled SS can
	   be recorded on the uncertified side.
	   (This will be higher than on similar lots of 5.25" disks. Based
	    on the tour I would guess it to be about 10% (5 out of 50))
	2) These disks will *always* cause excessive head wear on the disk   
	   head on the 'wrong' side because they are not burnished.
	3) The may not be capable of retaining data reliably on the wrong 
	   side. 

I don't know where you buy disks but I find that bulk disk usually go for
$1.00 ea for SS and $1.20 ea for DS. If you lose 5% because they can't be
formatted then you are actually paying $1.00/.95% good = 1.05 each. Or
saving about 15 cents per disk. The risks you are incurring are early
death of your disk drive because one head is reading an unburnished disk
and being sanded to nothingness, and having a backup go bad 'in the can'
because the oxide on the other side didn't have the retention power it
would have required to be certified. 

It's not worth it to me, but I am not you. You be the judge.


--Chuck McManis
uucp: {anywhere}!sun!cmcmanis   BIX: cmcmanis  ARPAnet: cmcmanis@sun.com
These opinions are my own and no one elses, but you knew that didn't you.