System disk specific to the IIc+?
schmidtd
gives you the option to format 800k floppies with 1:2 or 1:4
interleave. I thought there was something wrong with the IIc+'s
drive, it was going so slowly...
Anyway, on to my question. I read somewhere in my travels (can't put
my finger on it now, even given my best effort at googling) that there
was a system disk of some sort that allowed one to poke at system
settings like CPU speed and port configurations. I'm aware of how to
make it startup in slow mode (ctrl-open apple-esc-reset) and how to
set port baud rates, etc. through firmware. So it's not something I
especially *need*. But was there such a disk? And maybe an "Apple
introduces... Apple IIc Plus" sort of disk?
Michael J. Mahon
Just use the Zip Utilities disk--the IIc+ is logically identical to
the Zip Chip.
BTW, you don't need to hit Esc at the same time as the reset (which
can be *just* a ctl-reset, not a re-boot)--you can hit it shortly after
the reset and it will be recognized. Ctl-Reset / Esc is a good way to
switch to normal speed without losing loaded program(s) and OS.
-michael
NadaPong: Network game demo for Apple II computers!
Home page: http://members.aol.com/MJMahon/
"The wastebasket is our most important design
tool--and it's seriously underused."
touchstone
> And I now know why GSOS gives you the option to format 800k floppies
> with 1:2 or 1:4
> interleave.
i have seen that but don't know what that means. is this the same as
"high speed interleave"?
any advantages or disadvatages?
thanks,
matt
David Empson
> On 2008-01-31 08:15:58 -0700, schmidtd <schm...@my-deja.com> said:
> > And I now know why GSOS gives you the option to format 800k floppies
> > with 1:2 or 1:4 interleave.
>
> i have seen that but don't know what that means.
When writing to a floppy (on an Apple II or Mac), the data has to be
converted from its normal structure into an encoded form which is able
to be stored reliably on the disk. This process takes some CPU time, and
the writing process is also time critical, so the normal method is to do
a two stage "encode, then write" sequence.
The floppy drive is spinning all the time (once the motor is activated),
so if the sectors on the floppy are adjacent and the computer wants to
write two consecutive sectors, then after it has finished writing the
first one and encoding the second one, the drive has already rotated
part or all of the way through the next sector. This means it would have
to wait an entire revolution of the drive before it can write the next
adjacent sector.
This would cause a major performance hit, so to improve performance, an
interleaving technique is used. Sectors which are logically adjacent
(numbered 0, 1, 2, etc.) are spread out with other sectors between them
(on each track). The degree of separation is given in the interleave
factor. 1:2 means that logically adjacent sectors are at least two
physical sectors apart, and 1:4 means that logically adjacent sectors
are at least four physical sectors apart.
The reason for having different interleave factors is due to different
overhead for various drives, and CPU performance.
If the computer is fast enough and it has direct write access to the
drive mechanism, then it is possible to write to a 3.5" disk with 1:2
interleave at maximum speed, because the encoding can be completed in
the time it takes one sector to pass under the head.
If the computer is slower then the encoding process takes longer and
more than one sector will have passed under the drive head. It is
therefore necessary to use at least a 1:3 interleave to get best
performance, and in some cases, 1:4 may be required.
Some drives have even more overhead. A notable example is the UniDisk
3.5. This actually has a two-stage process for accessing the drive, with
a microprocessor inside the drive acting as a go-between. For writing,
the computer sends a sector of data to the drive's microprocessor, which
then writes it to the disk.
This is an alterating process: the UniDisk's microcontroller can either
be transferring data from the host computer, or writing it to the drive.
it also has to do the sector-level encoding. This means that the
sequence of steps is to transfer the data to the drive, then encode it,
then write it. The total time taken means that it can't even keep up
with 1:3 interleave, so it is necessary to use 1:4 interleave to get
best performance with a UniDisk 3.5.
For consistency, the computer only offers 1:2 and 1:4 interleave, as
this covers the fast ones (e.g. GS/OS and ROM 3 IIgs firmware, which can
do 1:2), and the slowest ones (UniDisk 3.5). In principle, someone could
create 1:3 interleave disks, which would be a little faster than 1:4 on
many computers, but might be a lot worse on others.
All of the above considers writing only. The same issues apply in the
read direction, but there are some enhancements which can be made, which
mean that for more advanced drivers it is possible to ignore the
interleave and read any disk at full speed. This is done by reading an
entire track into memory in a single pass, then sorting out the
interleave order and decoding all the sectors in memory.
For less capable drivers (ROM 1 IIgs firmware, or anything involving a
UniDisk 3.5), the disk is read one sector at a time, and the same issues
arise with interleave factors.
> is this the same as "high speed interleave"?
Yes.
> any advantages or disadvatages?
Speed.
If you pick the wrong interleave factor (determined by the drives and
computers in which the disk will be used) then you will get either a
major or minor performance hit.
If your computer and drive are fast enough to support 1:2 interleave,
then writing to a 1:4 interleave disk will be about twice as slow,
because the drive has to rotate twice as far to get to the next sector.
If your computer and drive are only able to keep up with 1:4 interleave,
then writing to a 1:2 interleave disk will be about ten times slower,
because an entire revolution of the disk will be needed to write
adjacent sectors.
In both cases, reading will either be just as bad as writing, or be
unaffected by the interleave, depending on the driver and hardware
implementation (if it can read entire tracks in one pass).
It is also worth noting that standard PC floppies are formatted with a
1:1 interleave, which they can achieve because the encoding step is done
in hardware (inside the disk controller). If you write to a 1:1
interleave floppy in an Apple ][ 3.5" drive, it will be about ten times
slower than it would if you reformatted it as 1:2 (or 1:4, depending on
your drive). The tradeoff is that the interleave will also reduce the
performance for a PC (e.g. 1:2 will take twice as long to read or write)
but on average you get best performance by increasing the interleave to
suit the slowest computer.
--
David Empson
dem...@actrix.gen.nz
Warren Ernst
David,
Great description! Thanks.
Now, do you happen to know, just for the sake of discussion, how
interleaving works with the SuperDrive and the SuperDrive Controller
Card?
-Warr
David Empson
> Now, do you happen to know, just for the sake of discussion, how
> interleaving works with the SuperDrive and the SuperDrive Controller
> Card?
Mostly yes. The SuperDrive card works like the ROM 3 IIgs firmware in
terms of its capabilities. It can cope with any interleave factor for
reading from a SuperDrive (or Apple 3.5 Drive) because it reads an
entire track into the memory on the card in a single rotation, then
locates and decodes the sectors in the appropriate order.
For writing, the host computer and operating system are probably
significant. If used on a IIgs with GS/OS, the SuperDrive is able to get
best performance with 1:2 interleave. Writing to 1:1 is much slower, and
1:4 is about half speed.
With ProDOS-8, the operating system can only supply data to the card one
sector at a time. Despite this, as long as the writes are done as
quickly as possible, the card should be able to keep up with 1:2
interleave on write. I don't know if I tested this.
Upon further reflection, this might also be an issue with writing from
ProDOS-8 on a ROM 3 IIgs using the built-in disk controller and an Apple
3.5 Drive. I'd have to do some tests to confirm that can keep up.
With a UniDisk 3.5 attached to a SuperDrive card, it is no better off
than a directly connected drive. The overhead of the extra processor in
the UniDisk and the seqential transfer then encode then write sequence
means that 1:4 interleave is still the best option for a UniDisk 3.5.
--
David Empson
dem...@actrix.gen.nz
schmidtd
"Apple introduces... Apple" thing again with just the smallest nod to
the IIc+ hardware.
One last thing I'm looking for: is there a manual scan available
anywhere? I see the IIc (non-plus) on the usual places (http://
www.apple-iigs.info/doc/home.htm, 1000bit.com, etc.) but nothing for
the IIc+.
magnusfalkirk
> I've found the Apple IIc+ intro diskette - amusing to play with the
> "Apple introduces... Apple" thing again with just the smallest nod to
> the IIc+ hardware.
>
> One last thing I'm looking for: is there a manual scan available
> the IIc+.
Dave,
I'm not sure if this is what you're looking for or not but I saw this
on eBay and thought you might be interested:
http://cgi.ebay.com/RARE-Apple-IIc-Plus-Owners-Guide-by-Apple-Computer_W0QQitemZ270139483114QQihZ017QQcategoryZ80075QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Dean