Weirdity with my 8" drive

[Randy McLaughlin]

From: "Vintage Computer Festival" <vcf at siconic.com>
Sent: Sunday, May 01, 2005 5:15 PM


> I've noticed something odd with my 8" disk drive.  It seems to produce a
> lot of errors on the last tracks on side 1 when using Anadisk.  Anadisk
> will report "Gap in sector" and "Data error" errors, usually on tracks
> higher than 70, and always on side 1.  The errors are also inconsistent.
> I use Anadisk to do a disk dump and note down the errors on one pass, then
> do it again and compare the errors on the second pass to the first and
> they are invariably different.  I used the sector editor to read one track
> over and over several times.  On most tries it gets errors.  The errors
> are inconsistent from read to read.  Sometimes some sectors will have
> "Gaps", other times data errors, and occasionally the entire track reads
> just fine.
>
> I have dumped some disks that are otherwise error free and the dumps have
> been consistent.
>
> What does "Gap in sectors" under Anadisk mean anyway?
>
> Is this just a case of disks that are just old and wearing out or
> something weird with my drive?
>
> Yes, I've cleaned the drive head, thoroughly.  But that wouldn't explain
> why this is only happening on the higher tracks now, would it?
>
> Thanks!
>
> --
>
> Sellam Ismail                                        Vintage Computer 
> Festival
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Every disk drive has a unique alignment, this means that one drive can 
read/write disks created on it but may have problems in another drive.

You can make slight a slight alignment adjustment and see if the errors are 
worse or not.  If the errors are worse move alignment the other way.

"Gap in sectors" refers to Anadisk assuming that there are missing sectors, 
this can happen when data is misread and Anadisk believes there is an odd 
sector number.

Having a disk drive "perfectly" aligned does not mean you can read all 
disks, if the disk was written with a mis-aligned drive and you need to read 
the data then you must adjust your drive to closely match the original 
drive.  Recovery can also be done with multiple drives where some drives can 
read some tracks but not others, later the track data can be cut and pasted 
together.

Even after aligning a drive it will still be unique for numerous reasons. 
Alignment refers to setting many mechanical adjustments on a drive to 
optimized tolerances, on two sided drives you need to offset each head 
off-center of tolerance to average them to optimized alignment.  Alignment 
is generally based on adjusting track 00 and the center of the disk, this 
means that the last tracks are least likely to be within tolerance.

As stated above the problem can be either your drive or the original drive 
but the result remains the same.  If you must read the disk you can play 
with the drive but be careful you may not be able to restore the drive 
without the proper alignment disks & tools.


Randy
www.s100-manuals.com