How Computers Work · Files & Storage Deep Dive · Lesson 1 of 5

File Systems

Meet the hidden index that tells your computer where every file lives.

The index that finds your files

Your files are saved on a drive as millions of tiny pieces of data. Something has to keep track of where each piece lives. That job belongs to the file system.

A drive is the part that keeps your files when the power is off. It can sit inside the computer, or be a USB stick you plug in.

A file system is the way a drive organizes and keeps track of its files. Think of the index at the back of a big book. The index doesn't hold the story. It tells you which page to turn to.

When you open a photo, the computer looks up its name in the file system. The file system says where the pieces are stored. Then the computer reads them and puts the photo back together.

The file system also remembers details about each file:

• its name and the folder it sits in
• its size
• when it was made and last changed
• who is allowed to open it

Different computers use different file systems. Windows uses NTFS, short for New Technology File System. Macs use APFS, the Apple File System, which Apple built for fast flash storage.

You rarely see the file system directly. It works quietly every time you save, open, rename or delete something. Phones work the same way, with their own file system hiding behind the Photos and Files apps.

To see which one a drive uses on Windows, open File Explorer and click This PC. Right-click a drive, like Local Disk (C:), and choose Properties. The General tab shows the file system.

USB drives, FAT32 and the 4 GB limit

USB sticks and memory cards often move between computers, cameras and TVs. So they usually use a simple file system that almost everything can read.

FAT32 is an old, simple file system from the 1990s. Nearly every device can read it, from game consoles to car stereos. Its big weakness is size. A single file on a FAT32 drive can't be 4 GB or larger.

A gigabyte (GB) is a unit for how much data something holds. A long HD movie can easily be more than 4 GB.

This causes a common puzzle. You copy a big video to a USB stick with lots of free space, and Windows says the file is too large for the destination file system. The stick isn't full. FAT32 just can't hold one file that big.

exFAT is a newer file system made for flash drives and memory cards. It doesn't have the 4 GB limit, and both Windows and Mac can read and write it. That makes it a good choice for a stick you share between the two.

A quick guide:

• NTFS: the main drive in a Windows computer.
• APFS: the main drive in a Mac.
• FAT32: older or small USB drives. Works almost anywhere, but has the 4 GB file limit.
• exFAT: modern USB drives and memory cards. Big files are fine.

On a Mac, you can open files on an NTFS drive, but you can't save to it without extra software. That is one more reason exFAT is handy for shared drives.

Changing a drive's file system means formatting it, which erases everything on it. You'll learn about formatting later in this course.