Copying DEC VAX set up disks rx50, help - test-drb@ccmp.vtda.org

4 Mar 2007

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Subject: Re: Copying DEC VAX set up disks rx50, help
   From: ard at p850ug1.demon.co.uk (Tony Duell)
   Date: Sun, 04 Mar 2007 03:00:37 +0000 (GMT)
     To: cctalk at classiccmp.org

  I dunno, RX50 format is easy to copy.  Make sure
that your 1.2M drive 
 is declared as such in the BIOS setup--if it's confused with a 1.44MB 
 drive, it's not going to work, as 2D operation on a 1.2MB requires a 
 write clock (300KHz) that conforms to a 360 RPM drive.  A 1.44MB 
 drive is 300 RPM--so any attempt to write a 2D format using a 250KHz 
 clock rate is guaranteed to fail--you'll run out track before you run 
 out of data. 
I once saw a PC multi-I/O card that couldn't do the 300kbps data rate, I 
think it just did it as 250kbps.... Needless to say that card went 
straight back to the suppliers...

Anyway, with so few people (other than on this list :-)) using 5.25" 
drives now, I wonder if most  modern PCs can still generate the 300kbps 
rate, If not, this could explain the problems the OP is having...

-tony 
Wrong.  The RX50 format and RX33 formats are very differnt.  The RX33
is PC compatable and was not used for VMS floppy sets.  The RX50 drive
is a Single sided 80 track (96tpi) double density drive with the oddity
of two spindles and one head positioner.  I have used FD55F as a single
drive repelacement as RX50s are not very reliable and noisy (acousticlly).
The RX33 drive (FD55GFR or similar) in the slow mode also works fine.

The problem is to fit 10sectors DEC used the WD1793 and fudged the format
some to truncate the Index mark gap and end of track gap.

The 765 will read this if: it is the 765A or 7265 and the drive is not 
running fast (works better if running 1% slow!).  The 765 has a built in
ship over index time and the later versions had this time shortend or 
eliminated in the case of the 7265.  The easy fix is slow the drive a 
few percent till it starts reading.  The hard way fix is to crank up the 
clock driving the 765by 2% (replace the 8/16/24or 32mhz clock with 
one 2% faster). It's harder as finding a clock that is just a tad faster 
is not common.  FYI: some PC floppy controller work better than others
due to implmentation differnces internal to the integrated flavors of the 
765 (9266, 8243, 37C65m 37C665...).

Me I cheat, I use either the PDP11 or a real microVAX with RX50 or rx33
and avoid the pain.

Allison