Subject: 8" RX02 floppies on IBM PC

From: [email-masked] (George Cameron)
Date: Fri, 17 Dec 1993 11:36:53 +0000

This has already been posted to the other groups mentioned, but Charles
Lasner suggested that I try alt.sys.pdp8 as a potential source of experts
in this area. Any suggestions very welcome!

[Posted to alt.sys.pdp8, comp.sys.ibm.pc.hardware, comp.ibm.pc.hardware, comp.sys.dec, comp.sys.dec.micro]

Maybe this is a FAQ, but I've not managed to find it anywhere. Let me know
if I've missed it, or if there's a better group I should be posting to.

1/ My questions:

(i)	Can I interface an 8" floppy drive to a standard PC controller on
	a PC clone computer? Do I simply need a conversion cable?

(ii)	Is there any software around (PD/commercial) which would allow me
	to read the RX02 format (written on an RSX system, so I guess this
	implies Files-11)? Do some PC BIOSs include 8" floppy support, and
	would this be any help to me (since it isn't an MSDOS floppy!)

(iii)	Alternatively, would it be possible for the RX02 controller on the
	RSX host to control a 3.5" or 5.25" drive, so that only a software
	driver would be required to read it on the PC? (ie. could the
	RX02 controller drive, say, a 1.44MB 3.5" drive, using only 77
	tracks instead of 80, and using 26 256-byte sectors instead of
	18 512-byte ones?

(iv)	Any other suggestions?

2/ A little background, for anybody interested:

We have an old PDP11/60 running RSX (v2.something I think) which is still
in use because of the equipment it is attached to. However, it is a little
fragile, and I'm told that the Unibus is full and its disks choc-a-bloc, so
it would not be easy/desirable to modify the system setup.

The primary data output medium for this machine is 8" RX02 floppy (no ethernet,
serial line too slow to be convenient), and we keep an old Microvax with RX02
drives in a corner and use TCP/IP to get the data from this machine onto our
Suns. However, the RSX machine and the microvax are actually on different
sites, about 20mins by car across town. In addition, we are about to set up
a PC based system as the main processing computer at the same site as the
RSX machine, so it would be a great improvement to the system if we could
transfer data via floppy between the PDP and the PC

			+	+	+

I hope somebody can help - please reply by email, and I'll summarize the 
replies I receive.

Thanks for your time,

George

 ---------------------------------------------------------------------------
 George Cameron                  [email-masked]
 Dept. BioMedical Physics
 Aberdeen University
 Foresterhill                    Fax:           +44 (0)224-685645
 Aberdeen AB9 2ZD                Telephone:     +44 (0)224-681818 ext 53195

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From: [email-masked] (krause)
Date: Tue, 21 Dec 1993 10:22:00 GMT

>	a PC clone computer? Do I simply need a conversion cable?
I have a 8" (ITT 2020) drive on my -486 PC. It's connected, via an adapter
cable to a secondary FDC.
I don't know, how to access a secondary FDC via the 'legal' PC-BIOS, but with
the shareware programm 'ANADISK' I can make dumps of many floppies from several
machines: IBM 5120 (all in EBCDIC!), CP/M-disks and VAX 780 disks.
I think, if the RX02 floppies are not hardsectored, it should be possible to 
read (dump) them too.

>	would this be any help to me (since it isn't an MSDOS floppy!)
Look for ANADISK, or if you attach your Drive to the normal controller, there
are some BIOS-calls to set the normal FDC to other sector numbers and sizes,
some PC-controller clones allow even to set them to single density!
I once wrote a turbo pascal programm to read and write CP/M disks, without 
one line machine code. 

Klemens Krause
University Stuttgart - Germany

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From: [email-masked] (Charles Lasner)
Date: 21 Dec 1993 18:37:21 GMT

In article <[email-masked]>,
>I think, if the RX02 floppies are not hardsectored, it should be possible to 

RX01 disks are FM, but industry standard.  I have heard conflicting
reports on the ability for a standard PC floppy controller card being able
to control FM disks by using special software (BIOS definitely can't help
you!) in conjunction with:

1)	Nothing.  Special software can make it work.

2)	Small hardware changes.

3)	Only works on some clone cards, not others.  Won't work on IBM card.

4)	Same as 3), but requires small hardware changes.

5)	Same as 3), but requires real IBM card or slavish compatible.

The card is based on the 765 chip, which can work with FM disks in principle.

>I once wrote a turbo pascal programm to read and write CP/M disks, without 

But the problem is RX02, not RX01.  DEC uses an incompatible cross between
single and double-density conventions in the RX02.  I doubt if any other
floppy controller than DEC's "hand-made" one can deal with the format. 
The headers are FM with MFM ID data and FM data preamble with MFM data in
the data areas.  The index is pure FM.  Most machines are based on
packaged floppy chips.  Name any that can switch modes in the middle of a
record.

cjl