Re: Apple disk drive...

[mjmahon@aol.com (Michael J. Mahon)]

Michael J. Sch�lke wrote:

>Michael Black wrote:
>> One reason the Commodore (and at least some Atari) drives are slow
>> is that they are connected to the computers via a serial port.
>> That tends to be relatively slow, if for no other reason than that
>> the bits go one at a time rather than in parallel.  
>
>No -- the CBM drives are slow because the serial port is controlled 
>directly by the processor, shifting out the bits in software, rather 
>than using a hardware shift register. 

Not my specialty, but didn't the original Commodore drives also
read a disk sector into in internal buffer before beginning to send
it to the computer?  Store-and-forward without cut-through adds
to drive latency.

Whether bits are shifted in hardware or software is not as
important as how _fast_ they are shifted.  Hardware can
do it faster, but the speed of an I/O bus is frequently set
by convention, to which either hardware or software must
conform.

That said, I expect that the C=64 serial I/O was not very
speedy.

However, ISTR that a _software_ mod (which I think changed
the software in both the C=64 OS and in the disk drive) got
a disk I/O speedup of several times, so it would be hard to
blame the slow speed on hardware or the lack of it.  ;-)
-michael

Check out amazing quality 8-bit Apple sound on my
Home page:  http://members.aol.com/MJMahon/