Date   : Fri, 11 Oct 1985 12:14:20 GMT
From   : Bob Halloran <bobh%pedsgd.uucp@BRL.ARPA>
Subject: Re: A way to read 48 tpi disks on 96 tpi drives?

Organization : Perkin-Elmer DSG, Tinton Falls NJ

In article <2229@sdcc6.UUCP> ir320@sdcc6.UUCP (ir320) writes:
>I am getting a new computer and need to decide whether to get 96 tpi drives
>or 48 tpi drives.  I know I get double the storage with 96 tpi, but I also
>give up disk compatability with them don't I?  Is there a way I could
>read/write a 48 tpi disks on a 96 tpi machine.  (The system is question
>is the new SB180 system described in Byte.)  Can other systems write disks
>for these drives?

A 96tpi drive CAN read disks written on a 48tpi drive; the second part
of the construction article for that same SB180 implies as much.  The 
BIOS needs some extra code to realize it must double-step for these
disk formats.  The major problem as I understand it is that in writing, 
the 96tpi drive lays down a narrower 'track' than the 48tpi drive (makes 
sense), which may either get lost against a previously written 'wide' 
track if the disk has been used before in a 48tpi drive, or simply be 
too narrow for the 48tpi drive's head to get a useful signal from.

Hope this helps. 

                                               Bob Halloran
                                               Sr MTS, Perkin-Elmer DSG
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