On Tue, Feb 19, 2019, 7:24 AM Paul Koning <paulkon...@comcast.net wrote:
> > > > On Feb 18, 2019, at 10:29 PM, Warner Losh via cctalk < > cctalk@classiccmp.org> wrote: > > > > On Mon, Feb 18, 2019 at 6:18 PM Bill Gunshannon via cctalk < > > cctalk@classiccmp.org> wrote: > > > >> ... > >> No, RX50 was a strange DEC format. RX33 is a 1.2M floppy. > > > > The RX50 was a single sided 800 block floppy. The first two tracks had no > > interleave. The rest has 2:1 interleave, though sometimes physical and > > other times logical. Strange in some ways, kinda standard in others. But > > it's still a floppy, and other than size, much like the RX33 with 1/3 the > > number of blocks. > > > > Warner > > That's not correct. > > RX50 is 80 track, single sided, 10 sectors per track (not the PC-standard > 9 per track). All tracks are 2:1 interleaved. There is a 3 sector skew > from track to track. And logical track 0 is physical track 1 (physical > track 0 is logical track 79). > The interleave is logical on the Rainbow. The drive is formatted to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, however after track 2 they are logically interlaved by the drivers in Venix, Dos and CP/M. There is no skew there, except for Venix... And on the Rainbow, tracks are purely sequential... Guess that lead me astray for the pdp-11 users... The MSCP controller does this; on a Pro it's done in the driver. I've done > it for RSTS, but it's easy to confirm by reading the source code of DEC > drivers such as the one in RT-11. > I stand corrected. Yet another odd quirk of this quirky media. I recall from back in the day there are other DECmate quirks... Warner >