19 Jun
2007
19 Jun
'07
2:16 p.m.
On 19 Jun 2007 at 14:24, Jim Leonard wrote:
> 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.
Yes, but the thing about XDF was that it used stock PC hardware. 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.
XDF fits about all one can fit using the NEC 765 hardware. Consider
that the unformatted capacity of a track is 12500 bytes. So using an
8K+2K+1K+512 = 11776 bytes, which means that 94% of the track is used
for data storage. Contrast this with the normal 18*512 scheme; 9216
bytes of data for a data density of 73%. Even DMF with its 21*512
layout only gets 86% efficiency.
You needed special programs and drivers to read XDF, but it was as
close to using all of the available storage on a diskette with PC
hardware as was possible.
Cheers,
Chuck