PDP-11 disk image question

Paul Koning paulkoning at comcast.net
Tue Feb 19 08:24:02 CST 2019

> On Feb 18, 2019, at 10:29 PM, Warner Losh via cctalk <cctalk at classiccmp.org> wrote:
> On Mon, Feb 18, 2019 at 6:18 PM Bill Gunshannon via cctalk <
> cctalk at 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 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.


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