Block allocation map: Difference between revisions

 

[[CP/M]] used a block allocation map in its [[Directory_(file_systems)|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.<ref name="cpm_pg">{{cite book|title=CP/M Plus Operating System Programmer's Guide|year=1983|publisher=Digital Research, Inc.|location=Monterey, CA|edition=Second|page=2-12,3-16}}</ref> 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.<ref name="cpm_pg" />