Re: Help with NIB, PO, and DO?

["Charlie" <charlied@NOSPAMbboard.com>]

"Jeffrey Theusch" <larva_jt1@yahoo.com> wrote in message
3b40f4a2.25501997@news.wi.centurytel.net">news:3b40f4a2.25501997@news.wi.centurytel.net...
> I am starting work on an ADT-like program called "ADS", Apple Disk
> Server.  It involves using a disk image selector interface and
> transferring the image to a temporary 5 1/4" floppy.  After it is
> booted, a restart of the Apple would result in transferring the temp
> floppy back to its original image file on the PC, updating any
> changes.  Other options would do simple transfers and other ordinary
> "stuff."
>
> I have most of the operation planned out, but for a few details, I
> need more information to continue:
>
> 1. A powerful feature of my new application could be the use of a
> variety of image formats, most notably NIB (You can make transfers of
> copy-protected disks and also preserve volume numbering!).  From what
> I now know, NIB is the format containing original disk bytes, right?.
> Therefore, a fairly simple routine could dump these bytes over a
> serial line.  But, how do you do this?  Each track must have a
> starting point and ending point, how do I detect this when the disk is
> spinning?

The original disk didn't really have distinct bytes on it.  It had a series
of zeros and ones and it was up to the hardware/software to determine where
the "bytes" started.  This was done by writing "self-sync" ( 10 bit ) bytes
to the disk.  Even then the other "bytes" were actually nibbles that were
combined in two different encoding schemes.  The volume#, track#, sector#
and checksum in the address field were odd/even encoded and the data in the
data field was 6 & 2 encoded.  There were also reserved bytes used as a
prologue and epilogue for each field.

>What order is the NIB disk image in relation to the
> physical disk?  And what about half- and quarter-tracks?  How are
> these managed?  Would a disassembly of Saltine's Super Transcopy help?
>
> 2. I know that .dsk files can possibly be in Prodos Order (.po) or DOS
> Order.  What are these orders, and how can I detect the difference in
> disk image files?
>

ProDOS order (at least as far as disk images are concerned) is simply
numerical order.  In other words the first block (512 bytes) on the image is
block 0, the second block is block 1 and so on.  This is not true on a real
disk where the blocks are separated into 256 byte sectors that are in a
skewed arrangement.  This skewing is different for DOS 3.3, ProDOS, Pascal
and CP/M.


> 3. Is there any basic info on the 2mg format that could help me
> incorporate it into my application?
>

A2Central has the format for 2mg files:
http://a2central.com/programming/resources/filetypes/ftn-e0.0130.html

> Any answers to any of my questions are greatly appreciated!  Any
> knowledge, however small, could help me complete my project.  Thanks!
>
> larva_jt1@yahoo.com

I would recommend that you get a copy of "Beneath Apple DOS" by Don Worth
and Pieter Lechner.
"Beneath Apple ProDOS" (same authors) is also recommended.
These two books cover most of your questions in detail.

I hope this helps,

Charlie