30 Jul
1999
30 Jul
'99
3:30 p.m.
Greetings!
I have a couple of Tandon 8" slimline drives (They're in the basement and
I'm not so no model number.) They clearly can't read one another's writing
consistently, so I'm interested in alignment data as well as the jumper
definitions. Would you have a manual which contains that information? I
need to know what the jumpers are and do, and what the factory default
settings are. I also need to know where the dif-amp outputs to be used for
alignment are located, (pin numbers) as well as the index sensor pin and
other signals used in adjusting these drives for radial head alignment,
index alignment, track zero calibration, etc. If you have it and could
email me that data, it would help greatly.
regards,
Dick
-----Original Message-----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp(a)u.washington.edu>
Date: Friday, July 30, 1999 7:23 PM
Subject: Re: Cromemco 4FDC, How do you format a disk?
> true and for the data I gave the 125kbits/sec rate
is too low. As it's
> minima was 250kbits/s is twice that! Part of the recording scheme is
that
there are
rules for continous strings of 1s and 0s, they arent permitted
to exist for clocking and bandwidth reasons.
I've seen plenty of controllers and data separators that put limits on the
maximum number of consecutive pulses and gaps. That's why you need clock
pulses in MFM recording, and why Apple had the 5-3 and 6-2 encoder tables.
I have _never_ seen a drive (and I've read OEM and service manuals for all
sorts of drives) that specify any restrictions on the user data using the
standard encoding schemes
At normal 5.25" data rates (125kbps (user bits) FM, 250kbps MFM) :
Repeated MFM 0's looks like repeated MFM 1's looks like repeated FM 1's,
and consists of pulses every 4 us.
Repeated MFM 1010... looks like repeated FM 0's, and consists of pulses
every 8us.
Now, all drives support user sectors of 1024 bytes (8192 bits), MFM at
least (and I don't think this is a real limit of the _drive_ either).
That means you could have either of the above patterns for 8192 bits --
the user bytes 'touch' each other with nothing between, and there's
nothing to stop you having a sector of 0's, a sector of FF's or a sector
of 55s if you want it. A disk drive that couldn't store said data would
not be useful.
I've got a Sony 3.5" drive on the bench at the moment. Now this drive
rotates at 600rpm, so you would double the above data rates. Some of the
tests involve recording pulses every 2us (corresponding to the first case
above) and 4us (corresponding to the second case above) continuously for
one revolution and then playing them back. The service manual for the Teac
FD235 gives tests involving the recording and reproduction of 250kHz
(pulse every 4us) and 125kHz (pulse every 8us) waveforms.
So it would certainly appear that these 2 drives could correctly handle
FM recording at half the user data rate of the standard MFM encoding. In
other words that Teac (720K) drive would handle FM encoding at 125kbps.
-tony