[Coco] Another Coco Virtual Disk Util

Robert Gault robert.gault at att.net
Wed Oct 23 11:35:28 EDT 2013


Wayne Campbell wrote:
> I may be mis-remembering something. I do recall that if I change the
> cluster size it will affect how many sectors are used when allocating space
> for a file, or to increase the allocation for a file. The minimum is
> 1-sector clusters, and over a certain size of drive space (I seem to recall
> it being $5A000) you cannot use 1-sector clusters.
>
> If someone knows what I am talking about, please feel free to correct me or
> back me up, whichever is required.
>
> Wayne

You can use 1 sector per cluster with almost any sized disk if you don't mind 
wasting an incredible amount of space in the OS-9 MAP. As you increase sectors 
per cluster (powers of 2) there is a tradeoff between effient use of the MAP and 
wasted space in the last cluster assigned to a file.

And no there is no right answer. :) That choice is left up to the enlightened 
user of OS-9. Ha!

More seriously, at some point the MAP can't indicate the number of used 
clusters. The MAP size must be indicated with 2 bytes DD.MAP so it can contain 
only $FFFF bytes or describe $7FFF8 sectors at 1 sector/cluster.
There are similar problems with large hard drives that are limited by DD.TOT to 
$FFFFFF sectors.

Robert





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