Re: Extracting files off “unknown” 8 inch disks. Any thoughts…

[Fred Cisin]

On Sat, 6 May 2017, Terry Stewart via cctalk wrote:
> ?Anadisk tells me the disks are Single Sided, Single Density.
>> It can see ID marks as it tracks a disk but that is all.  It can't see
> any data.
>> Could be an RX02 disk as people say....
>
> Oh, and sector size is 128 bytes.

Well, yes and no.

the RX02 can do a 128 byte per sector format in FM (single density)

BUT, then it can [OPTIONALLY] replace the content 128 byte FM sectors with 
256 byte MFM ("double" density) content, while leaving the FM sector 
headers in place.
Resulting in FM headers (that presumably SAY "128 bytes"), with 256 
bytes of MFM content.

In addition to the index address mark and related inter sector gaps, 
(check out P7 of: 
http://www.mirrorservice.org/sites/www.bitsavers.org/pdf/shugart/SA8xx/50664-0_SA800_801_Theory_of_Operations_Apr76.pdf
each header would have an ID Address Mark, the cylinder number, the head 
number, the sector number, and the sector size (0 for 128, 1 for 256, 2 for 512, 3 for 1024, 
but in THIS case, it seems to refer to the space provided rather than the 
actual content?), and a 2 byte CRC.  After a suitable gap for write 
splice, the content has a Data Address Mark, the content, and a 2 byte 
CRC.  Then another gap before the next sector.
(In THAT exaample, being single sided with 128 byte sectors, both the head 
number and sector size are listed as zeroes)


Bill deserves a beer just for his offer to help.

Allison's expertise is worth more than we could afford to pay for.