Re: Apple ][ plus 13 sector! Problems...

["Bryan Parkoff" <bryanparkoff@nospam.com>]

David,

    You might don't know that unknown version of DOS 3.x ignore to use 5-3
encoding and 6-2 encoding.  Then it uses 4-4 encoding for both header image
and data image that can only go up to 10 sectors per track.  It was done by
hacker whom they removed 5-3 encoding and 6-2 encoding by modifying DOS 3.x.
It was their experiment.

-- 
Bryan Parkoff
"Bill Garber" <willy46pa@comcast DOT net> wrote in message
zo2dnaRPp749bWTdRVn-uw@comcast.com">news:zo2dnaRPp749bWTdRVn-uw@comcast.com...
>
> "David Empson" <dempson@actrix.gen.nz> wrote in message
> 1gh4bdp.1ktjcxzfh4v2mN%dempson@actrix.gen.nz">news:1gh4bdp.1ktjcxzfh4v2mN%dempson@actrix.gen.nz...
> : "Bill Garber" <willy46pa@comcast DOT net> wrote:
> :
> : > "Bryan Parkoff" <bryanparkoff@nospam.com> wrote:
> : > :     It is what I understand that there are two different
> sequencer logic
> : > : PROMs.  First is to use 9 bits that it can only have one
> zero while
> : > : second is to use 10 bits that it can only have two zeros.
> It is why 13
> : > : sectors use 9 bits while 16 sectors uses 10 bits.
> : > :     Do you have 13 sector PROM that you can spare?
> : >
> : > The firmware can handle how many zero bits to look for.
> : > State machine only does what it's told to do.
> :
> : The state machine is different.  The 16 sector upgrade
> consisted of two
> : chips: PROMs P5A and P6A, one of which is the logic state
> sequencer, and
> : the other is the boot firmware.
> :
> : The 16 sector version of the logic state sequencer is able to
> read and
> : write 13 sector disks, but not the other way around.
> :
> : According to Inside the Apple IIe, there were changes in the
> read logic
> : to improve the reliability of reading 16-sector data.  I expect
> it
> : changed the timing tolerances to cope better with two adjacent
> zero
> : bits.
> :
> : Inside the Apple IIe has a full listing of the DOS 3.2 and 3.3
> versions
> : of the logic state sequencer, and there are differences in the
> code for
> : the read section.  I haven't looked at it in detail.
> :
> : > I would think the "State Machine" ROM would be the
> : > same. The data would be the same way per sector,
> : > just 3 less sectors per track.
> :
> : There is more to it than just the number of sectors per track.
> :
> : There are differences in the way the disk bytes are encoded on
> 13-sector
> : and 16-sector disks.  13-sector uses a "5-and-3" encoding
> technique,
> : while 16-sector uses "6-and-2".  (These terms refer to how data
> bytes
> : are split into bits to form disk bytes: "6-and-2" means that
> each data
> : byte of 8 bits is broken into a 6-bit disk byte and 2 bits
> which are
> : combined with 2 bits from each of two other data bytes to form
> another
> : disk byte.)
> :
> : The disk bytes are encoded using a table lookup technique
> (Group Code
> : Recording), which only allows some patterns of 1 and 0 bits to
> be
> : written to the disk (the restrictions are due to the
> reliability of
> : readback via the analog circuitry in the drive).
> :
> : From memory, the rules for 13-sector disks are:
> :
> : - Bit 7 must be set.  (This is a requirement of the Disk ][
> controller
> : for synchronization.)
> : - No byte may contain two consecutive zero bits.
> :
> : If you work out all the possible combinations, this gives
> slightly more
> : than 32 valid disk bytes, which is sufficient to allow a 5-bit
> encoding
> : technique.
> :
> : For 16-sector disks, they relaxed the restrictions slightly:
> :
> : - No byte may contain more than one pair of consecutive zero
> bits.
> :
> : This gives slightly more than 64 valid disk bytes, which is
> enough to do
> : a 6-bit encoding technique.
> :
> : Encoding one more data bit per disk byte allows fewer disk
> bytes to be
> : used to store an entire sector (about 341 disk bytes instead of
> 410), so
> : the sectors occupy less space and more can be fit onto each
> track.
> : --
> : David Empson
> : dempson@actrix.gen.nz
>
> Thank you David. I really must take some time
> and read through all these books. After all,
> I did buy them to learn from. What programs
> can I use to convert a 13 sector disk image to
> a real disk? From what you wrote above the 16
> sector controller should be able to still write
> one?
>
> Bill @ GarberStreet Enterprizez };-)
> Web Site - http://garberstreet.netfirms.com
> Email - willy46pa @ comcast DOT net
> Change DOT to a dot to contact me
>
>
>
> ---
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