Re: Help with NIB, PO, and DO?

[larva_jt1@yahoo.com (Jeffrey Theusch)]

On Mon, 2 Jul 2001 20:46:53 -0400, "Charlie"
<charlied@NOSPAMbboard.com> wrote:

>
>"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.

Do these books cover the low-level access of disk data?  I have wanted
to obtain "Beneath Apple (pro)DOS" for some time, but I am not into
spending much money for these great references.

Thanks for your help!

>
>I hope this helps,
>
>Charlie
>
>