Tarbell is making me insane - test-drb@ccmp.vtda.org

14 Nov 2007

...

Subject: Re: Tarbell is making me insane
   From: Grant Stockly <grant at stockly.com>
   Date: Tue, 13 Nov 2007 22:57:55 -0900
     To: "General Discussion: On-Topic Posts Only" <cctech at
classiccmp.org>

 FYI: 3.5" disks were never meant to run at
125khz.  The
720k mode is 250khz and the 1.44mh is 500khz.  The read
amps just may not work well down that low. 
Do you think that it would be better if I were to get the Tarbell to 
run at 4MHz (250kHz)?

I'd have to make a new BIOS and modify the format program.  I don't 
have source for the format program.  Does anyone off hand know where 
source to the Tarbell CP/M utilites could be found? 
Or utilities for any FDC based on 1771 could be modified.

...
 I should be able to format the disk as 36 sectors 80
tracks and 
possibly configure it to use both sides.  That would be formatting it 
to capacity...

I'm going to write a disk image tool that dumps the disk to my 
computer.  I could write one that also writes an image to a disk.

What do you think would happen if I were to try to use the disk at 
250kHz but only put half of the sectors?  Will the 1771 handle the 
extra time or give me errors? 
Take the time to read up on 1771 and FDC formats before you just 
plunge in.  You will arrive at a better solution and spare yourself
wasted time.

Not all 1771s where shipped as full speed parts too.

...
 This faster signal might be better for the disk drive?

Potentially.  Remember FM floppy recording was passe' by the early
80s with every one needed far greater space.  It want even a 
consideration buy time PC 3.5" floppies hit the street.

...
 It may seem strange I'm fighting with this so hard,
especially since 
I'm working on Altair disk drive system emulator using SD cards, but 
nothing beats real live hardware.  : ) 
I can understand wanting a floppy, a real floppy.  However I'd expect
a goal such as being able to read 8" SSSD (cp/m standard) or other 
widely used format for archival or transfer.

Another controller that ended up in altairs very often was the NS* MDS.
It's hard sector but there is a lots of media and programs for it's
DOS and also CP/M.  Getting floppies is a pain however.

Allison

...
 Grant  