Multi-platform distribution format (Was: Backups [was

Johnny Billquist bqt at
Mon Sep 21 04:30:48 CDT 2015

On 2015-09-21 02:11, Jerome H. Fine wrote:
>  >Chuck Guzis wrote:
>> >On 09/20/2015 03:03 PM, Fred Cisin wrote:
>>> >On Sun, 20 Sep 2015, ben wrote:
>>>> I was just digging in to old CP/M a bit and it was/is tied mostly
>>>> to the IBM 8" standard floppy and the floppy interface used at the
>>>> time. Even that gave a very small amount memory per track. Ben.
>>> single sided FM/SD 77 tracks, 26 sectors per track, 128 bytes per
>>> sector 256,256 bytes (250.25K)
>> There was a good reason for that.
>> Many early disk controllers did not have a "write index to index"
>> fucntion that also enabled writing special (i.e. missing clocks)
>> characters.  As a result, one had to purchase 8" floppies
>> pre-formatted (this actually persisted for quite some time).  IBM 3740
>> format was the most common format out there; hence the easiest to obtain.
> You bring up a VERY notable lack of support by DEC of that
> situation!!!!!!!!!!!!!!!!!!!!!!
> For both the DEC  RX01 and the DEC  RX02 8" floppy drives,
> while it might have been possible that DEC engineers were unable
> to initially figure out how to allow users to perform an LLF (Low
> Level Format) on the 8" floppy drives, it seems certain that after
> 3rd party manufactures figured out, DEC could also have supported
> that function as well.
> Instead, DEC pretended that all 8" floppy media HAD to be
> purchased PRE-FORMATTED from DEC.  Well, if you
> ever discussed that option with a DEC person, it certainly
> did not seem like the individual was pretending.
> After I managed to locate a DSD (Data Systems Design)
> drive which supported the DEC  RX02 floppy drive function,
> it was game over for that particular DEC monopoly.  The
> DSD drive was able to perform an LLF for either single
> density or double density in addition to being both single
> sided and double sided.

Not that tricky. All you needed was a way to format into RX01 format, 
which is plain simple IBM single side, single density format.
RX02 floppies have the same low level formatting. To use them in RX02 
mode just requires flipping a bit in the sector header, and the RX02 
drive is able to do that.

> Note that the RX50 was the same.  DEC finally changed
> their marketing policy with the RX33 drive which used the
> same 3.5" HD floppy media as the PC.  It was actually
> possible to FORMAT those floppies under RT-11.

No, DEC actually did support users formatting RX50 floppies on their 
own, but only on the Rainbow.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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