CP/M used a block allocation map in its directory. Each directory entry could list 8 or 16 blocks (depending on disk format) that were allocated to a file. If a file used more blocks, additional directory entries would be needed. Thus, a single file could have multiple directory entries. A benefit of this method is the possibility to use sparse files by declaring a large file size but only allocating blocks that are actually used.[2] A detriment of this method is the disk may have free space (unallocated blocks) but data cannot be appended to a file because all directory entries are used.[2]
Errata
The Commodore DOS used a similarly named but significantly different noting.