> -----Original Message-----
> From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu]On Behalf
> Of Harold Hallikainen
> Sent: 07 November 2006 19:03
> To: Microcontroller discussion list - Public.
> Subject: RE: [PIC] Interfacing a PIC to a microSD or TransFlash card
>
>
>
> >
> >> FAT32 goes up to 32GB in actual implementations
> > i have a 160 gig fat32 hard drive in an external caddy running just fine
> > with XP, i just had to format it using a win98 box.
> >
>
> Is the "limitation" how many sectors are allowed per cluster? Microsoft's
> FAT Overview says BPB_SecPerClus is one byte. Supposedly, for FAT16 (which
> is what I'm most familiar with), this could allow 255 sectors per cluster
> times 512 bytes per sector times about 65,535 clusters or 8.55e9 bytes per
> disk. This would be a cluster size of 262,144 bytes. The Microsoft
> document also says the cluster size must be a power of 2, so the maximum
> would then be 128, or 65536 bytes per cluster. It ALSO goes on to say you
> cannot have a cluster size greater than 32kBytes.
IIRC NT allowed you to break that rule and have 64k clusters, I remember the 98 resource kit saying that 98 could read and write fat16 partitions over 2 gigabytes but none of its disk utilities were comaptible with them.


> Is FAT32 similar, but with a larger FAT table, and with 32 bit cluster
> identifiers in that table?
i think that is the gist of it but i belive there are some other minor changes too.

according to wikipedia

"In order to overcome the volume size limit of FAT16, while still allowing DOS real-mode code to handle the format without unnecessarily reducing the available conventional memory, Microsoft decided to implement a newer generation of FAT, known as FAT32, with cluster counts held in a 32-bit field, of which 28 bits are currently used."

so that would mean 256 megaclusters

which keeping the 32K cluster size limit would mean 8 terabytes

i don't know why wikipedia says the actual limit is 2 terrabytes and i don't have any ms docs handy to compare but either way its big enough not to be a worry for most hard drives just yet.


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