8 Oct
2005
8 Oct
'05
8:38 a.m.
> > data in a smaller area. The highest density
8" media I ever had was
> > DSDD, or 720K on the big 8" surface. That's a LOT larger disk and
> > hence a much
> It was actually closer to 1.2M. In fact the 1.2M IBM PC/AT format is
> almost exactly the same as a standard 8" format (it's the same data
> rate, same rotational speed, etc), the main difference being that the
> 8" drive has 77 cylinders, the 5.25" drive 80.
On Fri, 7 Oct 2005, Scott Stevens wrote:
I was pretty keen on the drive space available to me
back when I was
running my BigBoard system (Xerox 820 clone) with two DSDD 8" drives. I
am almost certain the formatted capacity with CP/M was 720K with those
drives. I remember it so distinctly because when I 'upgraded' to a
PC-XT clone, I was suddenly downsized to 360K per disk, exactly half the
space. Is it possible that the 1.2M capacity is like the 'advertized'
2M capacity that 3-1/2" 1.44 floppies sometimes have printed on them?
Meaning, is that the raw unformatted capacity of the drive?
NO.
The unformatted capacity is about 1.6M.
Each track (77 tracks per side * 2 sides) can hold about 8 sectors of 1024
bytes each, or about 15 sectors of 512 bytes, or about 28 sectors of 256
bytes.
The ONLY difference in format between a DSDD 8" drive and a "1.2M" 5.25
(which were originally created specifically as a drop in replacement for
8"!) is: 77 tracks per side on 8" V 80 tracks on "1.2M" 5.25"
--
Grumpy Ol' Fred cisin at xenosoft.com