Re: PC to Apple II disk drive

[heuser.marcus@freenet.de]

Jack Tseng wrote:
>
> Not always, like Atari 8bit Disk drive is a drive, not a computer with its
> own cpu,

Not true.
It has it's own CPU (a 6507), a 4KB ROM/EPROM, a RAM (6810), an I/O
controller (6532 RIOT) and a FDC chip (WD2793). It's nearly as complex
as the Commodore 1541 - and much more complex than the Apple Disk II
and its controller. Schematics are readily available on the net.

> there is NO DOS programmer in ROM.
> It requires Atari DOS software to boot up.

The Atari drive is essentially a C64-drive without "higher disk
functions" in ROM. It supports low-level functions (load or save a
block of data, format the disk).
But as the Atari computers OS ROM has only the generalized I/O system
(CIO) and the handler for the serial interface (SIO) built in, it needs
a handler ("driver") for block and file functions - a file called
DOS.SYS - to integrate with CIO and SIO.

The menu based user interface (for us puny humans) - which the
Commodore's usually don't provide - is in the separate file DUP.SYS.

Here is a good explanation of the disk system of the Ataris and which
parts are loaded from disk and which parts are already in the Atari OS
ROMs:
http://www.atariarchives.org/iad/chapter1.php

> PC can communicate with the dumb disk drive in APE SIO cable
> with a serial connection.

That's because the Atari drive is intelligent enough to deliver or
accept data in block form, when nicely asked.
That's the main difference to the Apple floppies: The user/program/DOS
sends a whole block of data (usually 128 bytes) to the Atari floppy via
CIO and the drive tries to process it all by itself.

> Apple Disk Drive seems more more diffcult than C1541 and Atari 1050.

That's because the CPU of the Apple computer itself - with some sort of
DOS loaded - really controls the drive (through some "mechanisms"
provided by the disk controller).
Therefore the DOS of the Apple has to provide the low-level routines -
which also opens the door wide open for modifications of all sorts.
Hence some very creative copy-protection schemes, hence many different
disk formats.

The Apple CPU has to get the timings right, too - which probably is the
#1 reason that there is no "simple cable with a bit o' software"
solution for the PC out there. Electrical interfacing completely aside.

bye
Marcus