Different operating systems use different file systems, how you organize files (usually in a hierarchical structure) on some sort of disc.

Basic kinds of disk drives (solid state, optical, magnetic)

ROM   what's in memory is fixed.
RAM   you can read or write, but when the power is shut off, all the 1's become 0's.
PROM  You can set a 0 to 1, and it remains a 1 thereafter.  (Like a burnable CD, WORM)
EPROM  You can set a 0 to 1, and a 1 to 0, but it takes "radiation" to set the 1 to 0.
EEPROM  You can 0 to 1, 1 to 0, both electrically.  And it's locked in, until you change it (solid state).

Anyway, whatever format of disc you have, it's still just a collection of bits.  A file system is one that organizes itself in such a way as to give the illusion that the disc really does have separate discrete files on it.

What do we want from a file system?

--> A hierarchical file structures (folders, subfolders).
--> Usually permissions (although some file systems don't have them.  ISO CD file system, FAT-based systems, FAT, FAT32, exFAT, usually find them on flash drives)
--> Filenames, and other information about the files.  (Access, modification, creation dates).
--> Files should be able to modified, including growing and shrinking.
--> Recovery systems.  The computer crashes while I'm saving something onto the drive.  I restart it.  Ideally, you don't lose much in these situations.

NTFS:  New Technology File System (modern Windows file system, but Linux can use it.)
Maximum file size:  16 Exabytes = 10^18 bytes.
Kilo, mega, giga, tera, peta, exa, zetta, yotta, ronna, quetta
Maximum partition size is 256 TB (odd since a file can be 16 EB, but you can't store a 16EB file on a 256 TB partition).
Designed for Windows, Linux can use it, but less efficiently.
Encryption, compression, journaling (journaling is when you keep track or changes made to the disk in the event of catastrophic failure and you need to restore stuff.


EXT4:  Linux (Extended File System version 4).

Maximum file size:  16 TB
Maximum parition size:  1 EB
Designed for Linux, Windows can't do much with it, except read.
It can journal, but no encryption or compression.