23 Mar
2010
23 Mar
'10
8:04 p.m.
On Tue, Mar 23, 2010 at 3:32 PM, Roger Ivie <rivie at ridgenet.net> wrote:
On Tue, 23 Mar 2010, Gene Buckle wrote:
Ordinary "PC" 3.5" drives don't change speed, but Amiga high-density
drives do - they spin at 150 RPM when high-density media are inserted,
maintaining the double-density data rate. This is because it was
judged more economical to make a custom drive than to design a new
Paula chip (for those that don't know, unlike in a PC, with the Amiga,
there is no single "floppy controller" per se - the necessary
functions are performed by a combination of CIA I/O pins, a massive
shift register in the Paula chip and logical miniterms applied by
Agnes to decode/encode the data to/from MFM). One advantage of
changing the drive vs changing the chip is that any Amiga can take an
HD drive, not just new models (the HD drive came in around the same
time as the A3000, IIRC). The official drive may be the Chinon
FZ-357A, but I am not in the room with an Amiga to verify that.
It's unlikely to run across one of these drives outside of an Amiga
context, but they did exist (and I do have a couple of them - they
even work under emulators like A-Max and Shapeshifter to read
high-density (FDHD) Mac disks).
How are you going to handle the data rate difference? ?If memory serves,
using ?1.44MB media results in a higher RPM and a higher data rate.
3.5" drives don't change speed; they always run at 300 RPM. That's why
HD diskettes hold 1.44MB instead of 1.2MB. The DEC RX33 5.25" drive *does* change speed. It
runs at 300 RPM for DD
media and 360 RPM for HD media.
That's interesting to note, considering the RX33 is a
specifically-strapped Teac FD55GFR (usable on a "regular" PC when
suitably re-strapped).
-ethan