Multi-platform distribution format (Was: Backups [was

Holm Tiffe holm at
Mon Sep 21 12:22:07 CDT 2015

Johnny Billquist wrote:

> Not that I care what Holm Tiffe smokes, but I can at least comment what 
> you write, Tony. :-)
> On 2015-09-21 16:02, tony duell wrote:
> >
> >[Russian PDP11-a-like]
> All bets are off when we talk about clones, since they might be rather 
> different in details...
> >>I've tried to boot an RX01 Floppy in RX02 mode, that failed on all disks
> >>I've tried. Is an original RX02 able to boot (RT11) from an RX01 disk?
> >
> >As far as I know, it can't. An RX02 can read/write an RX01 disk, but the 
> >software
> >interface to the controller is so different (the RX)2 uses DMA, the RX01 
> >doesn't for
> >one thing) that the RX02 cannot boot an RX01 disk.


I don't know if the Controller board (Inside the Computer) would
be "RX02-able" when I read this.

Just FYI:

That's the I4 Controller board that is connected with a flat cable to the
Drive..working as RX01 at least..

And that is the Controller Board in the Drive itself, the red cable goes
tro the I4 Board in The computer:

..and if I look at this picuture it looks more that it contains AM2909
sequencers instead of an AM2910..

> Of course an RX02 *drive* can read an RX01 *floppy*. And yes, a system 
> with an RX211 and an RX02 *drive* can boot from a floppy that what 
> written by an RX01 *drive*. But you need the boot code for an RX211 
> controller, and that boot code also needs to handle RX01 format 
> floppies. If the boot sector on the floppy is for an RX11, then no, an 
> RX211 will not understand things. The programming model for the two 
> controllers are different. You need different device drivers.
> But this is really a question about the controller and the software 
> running it, not the floppy or the drive.
> >>I know that a different device driver has to be used  normally, but I had
> >>no RX02 media and wasn't able to make one, since the machine has no other
> >>drives connected and the card cage is mechanically not compatible (metric
> >>dimensions including the fingers).
> >>I know that in the RX02 Mode the Drive has an format track command that
> >>doesn't exist in RX01 mode, that's documented. How about the RX02?
> >
> >The RX02 has a 'set density' command that can be used to reformat a
> >formatted single density disk as double density.
> Yes. And it's just flipping a bit in the sector header. And the drive 
> changes between the densities for the data part of each sector. So you 
> can actually have different densities on a per-sector basis with an RX02 
> drive.
> >>Is there somewhere a picture from the Conteroller PCB of the DEC RX02
> >>(just to look at). The russian controller has a 2910 and four 2901 if
> >>I remember correctly... (K1804VU1 and 4xK1804VS1)
> >
> >The RX02 drive contains a couple of 2901s and a few of the sequencer chips
> >(I think 2911s, maybe 2909s). I've seen a 3rd party Qbus card that 
> >connected to
> >normal Shugart drives and which could red/write RX02 disks, I think that 
> >had
> >a couple of 2901s and a 2910 on it.
> What people need to understand is that there are a bunch of controllers 
> and combinations. If we just contain our self to Unibus controllers, we 
> have two. The RX11 and RX211. The RX11 works with both the RX01 and 
> RX02. However, an RX02 needs to be set in an RX01-compatible mode if 
> used with an RX11 (a couple of dip-switches in the drive). And that also 
> turns it into essentially an RX01 (can't deal with double density within 
> the RX11 interface). The interface to an RX01 is different than the 
> interface to an RX02, even though they use the same flat cable.

Ok, got it. But I know that this russian drive has the described Jumper
for switching between RX01 and RX02, but I don't know what this requires as
Controller in the computer...

> The RX211 can be used with both an RX01 and an RX02, as far as I can 
> remember. But that implies that there would need to be some switch or 
> jumper on the RX211 in order to interface it with an RX01 (or some 
> automatic detection), and I can't remember seeing that. But it might 
> just be my memory failing me.
> But the RX211 works differently than the RX11, so from a program point 
> of view, they are totally different.
> The RX02 drive, then, in turn, can read and write both RX01 and RX02 
> floppies. No special tricks are required. The drive will detect, for 
> each sector, which format it is in, and will switch mode accordingly, 
> and return the right about of data (RX02 sectors holds 256 bytes, while 
> RX01 sectors holds 128 bytes). The software can thus also easily see 
> what type of floppy it is reading.
> RX211 device drivers obviously then can handle both RX01 and RX02 
> floppies, when used with an RX02 drive. And from the software point of 
> view, the sectors just contains different amount of data.
> 	Johnny



      Technik Service u. Handel Tiffe,, Holm Tiffe, 
     Freiberger Straße 42, 09600 Oberschöna, USt-Id: DE253710583, info at, Fax +49 3731 74200, Mobil: 0172 8790 741

More information about the cctalk mailing list