Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!iuvax!cica!tut.cis.ohio-state.edu!pt.cs.cmu.edu!b.gp.cs.cmu.edu!ralf
From: ralf@b.gp.cs.cmu.edu (Ralf Brown)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 1.2meg/360k compatibility question
Message-ID: <5505@pt.cs.cmu.edu>
Date: 13 Jul 89 14:12:02 GMT
References: <IYiAOwy00UhBI1IEMx@andrew.cmu.edu> <1567@westmark.UUCP> <5560@tekgvs.LABS.TEK.COM>
Organization: Carnegie-Mellon University, CS/RI
Lines: 89

In article <5560@tekgvs.LABS.TEK.COM> keithe@tekgvs.LABS.TEK.COM (Keith Ericson) writes:
 [things are actually a little more complicated, so I've expanded the diagrams
  for a closer look]
}     
}     Data track of a bulk erased diskette:
}     
}     )(*)(&(*^(*&%*&^$(*&^$%#%#$#!@!#$@^&%%#*&^%*&^%%$$$%
}     ^%&$(*&%%^#*(&%*%(*&%*%#$)(*&)(*$%$%@%^$(*&)(^&^%#()
}     )(*)(&(*^(*&%*&^$(*&^$%#%#$#!@!#$@^&%%#*&^%*&^%%$$$%
}     )(*&^*&^$^&*^()^)(&*)(^(*$%*&^$*&^%(&^)(*&(*%*&^$*&^
}     !@#$!@#$!@#$!@#%#@$%^$()%^&%^(^&*()&*)*(&)(%^&%&%$#@
}(1)  (&*()%^&%^^@#$#@!%#%^&(&*()*()_%$%#!@%$*^&)(*(&@#!%$
}     !@#$@#%^$%^*^&(*&*)(&*(%$#%@#$%^#$^&%*^&*(&*)*(&_)(*
}     ^#@&^%)(&*(*^&%^%#(*&%^#*(^&%)(*&^*%&$@&*^%(%&^%#&^^
}     %$##!^&$##@&^%#^#@&^%#&*^%$(*&%)(*^*%$(*%)(*(^%^%#&^
}     +*)(&^%*%#_)((^&$$$@)(**&_)&(&%&$#$)(**^&$^#_)(&*%&$
}     %$##!^&$##@&^%#^#@&^%#&*^%$(*&%)(*^*%$(*%)(*(^%^%#&^
}     
}---------------------------------------------------------------------------
}     Data Track of a 360K-drive formatted diskette:
}     
}     )(*)(&(*^(*&%*&^$(*&^$%#%#$#!@!#$@^&%%#*&^%*&^%%$$$%
}     ....................................................
}     ####################################################
}     ####################################################
}     ####################################################
}(2)  ####################################################
}     ####################################################
}     ####################################################
}     ####################################################
}     ....................................................
}     %$##!^&$##@&^%#^#@&^%#&*^%$(*&%)(*^*%$(*%)(*(^%^%#&^

Where the ..... is the erasing done by the tunnel-eraser after the head does
the actual writing.  If you look closely at the head, it looks like this:

		     ############
	#############
	#############
		     ############
	  ^^^	   	^^^
	read/write   tunnel eraser
	   head
}     
}---------------------------------------------------------------------------
}     
}     Data Track of a 360K-drive-formatted diskette WRITTEN with a 360K drive:
}     
}     )(*)(&(*^(*&%*&^$(*&^$%#%#$#!@!#$@^&%%#*&^%*&^%%$$$%
}     ....................................................
}     1234567890123456789012345678901234567890123456789012 \
}     1234567890123456789012345678901234567890123456789012  \
}     1234567890123456789012345678901234567890123456789012   \
}(3)  1234567890123456789012345678901234567890123456789012    >---data
}     1234567890123456789012345678901234567890123456789012   /
}     1234567890123456789012345678901234567890123456789012  /
}     1234567890123456789012345678901234567890123456789012 /
}     ....................................................
}     %$##!^&$##@&^%#^#@&^%#&*^%$(*&%)(*^*%$(*%)(*(^%^%#&^
}     
}---------------------------------------------------------------------------
}     
}     The above Data Track WRITTEN with a 1.2M diskette:
}     
}     )(*)(&(*^(*&%*&^$(*&^$%#%#$#!@!#$@^&%%#*&^%*&^%%$$$%
}     ....................................................
}     1234567890123456789012345678901234567890123456789012  <-- unerased data
}     ....................................................
}     ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ \
}(4)  ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ  >--data
}     ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ /
}     ....................................................
}     1234567890123456789012345678901234567890123456789012  <-- unerased data
}     ....................................................
}     %$##!^&$##@&^%#^#@&^%#&*^%$(*&%)(*^*%$(*%)(*(^%^%#&^
}     
}---------------------------------------------------------------------------
}     
}Now - guess what kind of problems the 360k-drive is going to have when it
}tries to read track (4).
}
}A(nother) 1.2M drive (assuming it's properly aligned) WILL be able to read
}track (4).

-- 
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