19 Jun
2007
19 Jun
'07
3:47 p.m.
On 6/19/07, Chuck Guzis <cclist at sydex.com> wrote:
On 19 Jun 2007 at 14:24, Jim Leonard wrote:
The Mac did this, but the Amiga did not. The Mac single-sided 400K
drive did vary the drive speed - you could hear the zones. Later Macs
varied the clock rate through the IWM (Integrated Woz Machine), part
of the disk circuit.
Amigas had the same number of sectors per track throughout the entire
disk - 11 sectors of 512 bytes. They did, however, use non-standard
hardware rather than an off-the-shelf diskette controller like early
PCs. The digital control lines (step, motor on, etc.) came from one
of the 6821/6522/6526-like PIO chips (8520s to be specific), and the
raw MFM data was shuffled through a 4096-bit shift register in the
sound chip (Paula). The final component was the MFM<->binary
converter that was done as a series of logical mini-terms by the
graphics chip (Agnes). The effect of all of this was that an entire
track was slurped or dumped at once, allowing a very small
inter-sector gap compared to designs that read and wrote random
sectors on a track, leaving room for those two extra sectors compared
to the ordinary PC format.
Commodore did vary the bit clock to create 4 zones of sectors on 5.25"
floppies (2040/3040/4040/2031/1541/1571 for the PET, VIC-20, and
C-64).
-ethan
If I were to implement some additional-storage
format, I'd
probably put
more/larger sectors on the outer tracks where there is more surface
area. I believe Mac and Amiga formats did this, although I'm not aware
of the particulars.
Mac and Amiga used hardware that was very different--and varied the
rotational rate or the data clock rate to achieve their "zoned"
recording format.