A key to getting good performance out of the FAT filesystem using a limited-memory processor such as the propeller is to format your card with the largest sectors you can. Generally this means 32K clusters (on any card sized 256MB or larger). This also means that cards of 256MB or larger will, in general, perform better than smaller cards, just because they can use larger clusters.

This code does not support FAT12, which means for cards smaller than 256MB, you will not be able to use 32K clusters. Refer to the table below and select the largest allowed cluster size. 

          min   max
   4M     512   512
   8M     512    1K
   16M    512    2K
   32M    512    4K
   64M     1K    8K
   128M    2K   16K
   256M    4K   32K
   512M    8K   32K
   1G     16K   32K
   2G     32K   32K
To format a card using Windows, you can either right-click on the drive in Windows Explorer and select Format. In the Format dialog, select FAT and set the cluster size appropriately.

Alternatively, you can use the command line with a statement such as 

   format /a:32k /fs:fat x:
where x: is replaced by the appropriate drive letter. (Be careful not to format your system disk!)