I am doing a project with an SD card and FAT32. The largest cluster size I can deal with is 4K. I am trying to find where the sizes are defined. I looked at a 16GB SDHC (UHS 1) and it will do 4K clusters, and a 32GB (UHS1) card bottoms at 8K. My question is this: Are these numbers written down somewhere? I need to tell my customers which cards will work.