Faster is Sometimes Slower!

[+Larry]

Today, I decided to make images out of my 720K Utility Disks. Since these disks span a very long time (back at least to 1990), I have disks that were formatted for the original Bob Woolley 3.5" XF upgrade, then the CSS XF upgrade, and finally the BB Floppy Board. These interleaves in double density are something like 9, 5, and 2. Of course, being parallel, the BB disks virtually fly. But guess what -- I can sector copy the slower disks *faster* to APE images than the other two -- by a wide margin. How? By not buffering the disk reads. In other words, I have a sector copier that does a R/W, R/W, R/W... instead of R,R,R,R...

 

The trick is that depending on the interleave, a slower interleave can have sufficient time to R+W instead of just reading. However, on the faster interleave disks, this doesn't work since there is insufficient time for R+W before the succeeding sector. Instead, it must wait for another complete revolution. On a hard drive, it matters little, because the rotational speed is so (relatively) fast. But even on a HD, not buffering is a little faster. I didn't make this discovery myself, another user pointed this out to my disbelief.

 

-Larry

Edited June 28, 2007 by Larry