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Re: [Freedos-user] [Freedos-devel] writing a loadable block driver for 4k-sector drive (Questions) C. Masloch Mon Feb 20 17:00:42 2012

>> NOTE: Transformation of sector sizes is easiest in FAT32.
>> Other FAT sizes may take more effort.
>
> I don't think so. Why would they? Cluster size stays the same, no  
> FAT-related special handling (which would be more complicated for, say,  
> FAT12) is necessary as far as I can tell.

Sorry for replying to my own message, but I just thought of something here  
again. You're probably referring to the root directory alignment handling,  
which of course is not needed in FAT32 as its root directory is not in a  
specifically reserved area.

As I noted in our (Eric) previous correspondence, the special case where  
some rounding is required (which might imply an incompatibility) doesn't  
usually occur (as formatting software usually leaves no unused directory  
entries in the last sector).

>> You CANNOT transform from
>> 512 to 4096 usually, as format tools do not take care to
>> align things in a way that would make this easy enough.
>
> True.

Another additional note, as I went thinking about this a bit. Only cluster  
values are stored in the FS (think FAT contents, FSINFO, and "start  
cluster" fields of directory entries) apart from what is in the *BPB, so a  
runtime upwards sector size transformation (say, from 512 B to 4 KiB, or  
 from 128 B to 512 B, or whatever) is still possible, just more  
complicated. I'm not certain, but my intuition is that it'd still be  
rather trivial to do.

As might be thought to be implied, transformation from 512 B away seems  
rather pointless now, but as I remarked in the previous paragraph, an  
"upwards" transformation could be /to/ 512 B if the stored file system  
(whether it is stored on some physical medium, in a file as an image, on a  
RAM disk, etc) uses smaller sectors.

regards,
C. Masloch

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