NTFS : WINDOWS

EXT4 : LINUX


EXFAT : Removable memory.  Flash drives, External Hard Drives.

FAT  stands for File Allocation Table.  And this was the file system for things like Windows 95 and Windows 98.

Why would I format my external hard drive to EXFAT rather than NTFS since my main drive is already NTFS?

NTFS is a more sophisticated system.  And external hard drives may not need that sophistication.  In fact, that sophistication may be a disadvantage.

For example, a FAT file system has no usernames.  It has no permissions.  It has a hierarchical file structure.  (folders, subfolders).  But it is not designed for a multiuser system.

If you format an external hard drive for NTFS, then all of your files have owners, and permissions.  So, if you remove your NFS external drive and plug it in somewhere else, it won't work.  Because your files are owned by a specific user, and on that machine, that user isn't there.

It isn't a lost cause, but you have to "take ownership" of the files.  And elevated process (an administrator process) has to go through every file and adjust the owners and the permissions.

But if your hard drive is exFAT, then it is essentially Plug-n-Play.  This is why Flash drives are ALWAYS formatted with exFAT (or other variants such as FAT32) so that you can transfer them between machines.

I have found my life to be easier if I format EVERY external hard drive with exFAT.

CDFS (ISO 9660) : CD-ROMS (DVD-ROMS and Blu-Ray ROMS and 4K-ROMS):
  DVD 720x480   Blu-Ray:  1920x1080   4K:  3840x2160
--> read-only.  Once you burn your files to the disc; that's it, you're done.  But files are stored hierarchically.  (Folders, subfolders).  It works just like a disc drive, EXCEPT you can't write to it AND opticals are notoriously slow.

Nearly every file system has to deal with fragmentation.  (CDFS file systems do not as they are read-only).

Fragmentation:  files can grow and shrink.  Directories can grow and shrink.  As files get added and deleted.  And files get larger what happens is that related files may be stored in entirely different part of the disc.  Or as a file gets larger, the newer part of the file may be stored in a different part of the disc because there isn't any more room in the current part of the disc.  If a file shrinks, then the part of the disc that held that last part of the file is now free, but depending on the file system, that portion of the disc may or may not get reused easily.

Eventually, over time, the disk becomes a mess.  With files and portions of files all over the place, and you can run out of disk space, even if there is lots of unused spaces scattered all over the disk.

So, you can defragment.  Defragmentation is a process whereby the files and fragments are moved around so that files become contiguous again and the used space is all together and the free space is all together.

Modern defragmentation often can solve the problem just by moving stuff around on the disk itself without using an external tape or anything.

APFS - Although modern MacOS (since OS X) has a BSD-Unix core, what is one fundamental difference between a Mac file system and a Linux file system?  Mac filenames are case insensitive.  Linux files are case sensitive.

In fact:  NTFS, exFAT, CDFS, APFS all have filenames that are case insensitive.
EXT4:  case sensitive

APFS:  uses Copy-On-Write.  When you make a change to a file, it doesn't overwrite the original file.  It makes a copy of the file.  (Not quite correct.  It writes the new data to a new block and changes the pointers in the file to point to the new block rather than the old block.)

APFS is Mac-proprietary and only runs on Mac systems.