The FLOP filesystem is designed for the use with the Mackapar 3.5" Floppy Drive (M35FD). The M35FD consists of 1440 sectors of 512 words each (737,280 words total).
The first seven sectors are the main header, followed by the file list. One block is a sector. It just stores pure data. Blocks are allocated back-to-front, to reduce collision between the file list and the data blocks.