lkml.org 
[lkml]   [2008]   [May]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: floppy question of the hour
Gene Heskett wrote:
> This is a 250 kilobaud data rate format, the maximum the WD-1773 FDC chip in the
> target machine can handle, with 18, 256 byte sectors per track, two sides=73728
> bits to write a track, /250000 (baud rate)=0.294912 seconds to write one full
> tracks worth of data. 80 tracks=23.59296 seconds to write the whole disk if it
> were streaming, but it takes 3 minutes and change? And nearly 2 to read it
> back as above? Odd. With the interleave of 3, I could see 75 seconds maybe
> for efficient methods. I also understand this is a one size fits all scene
> too, and that there must be compromises.
>
> I format these DD discs in the target machine with an interleave factor of 3 cuz
> that machines cpu is running at as low as .89MHZ and can't handle the read data
> any faster than that.
>
> Is this non-1 interleave responsible for the slowness of the writes or reads on
> this box? I can control the interleave on the target box, so I suppose I could
> test that effect easily enough.

Yes, the interleave slows you down, since after accessing sector 1, the
head must wait to pass over 3 other sectors before finally reaching
sector 2, therefore, you can only read 1/4 of the sectors on the track
each revolution of the disk. That leaves 4 revolutions at 300 rpm
giving 0.8s to read a track, or 64 seconds to read all 80 tracks, plus
seek time. That still does not explain 3 minutes though... not sure
what else could be slowing you down.




\
 
 \ /
  Last update: 2008-05-28 00:01    [from the cache]
©2003-2011 Jasper Spaans