A file system is the set of rules an operating system uses to organize data on a storage device: how files are named, where their pieces live on the disk, what metadata (dates, owners, permissions) is kept and how free space is tracked. When you format a drive you choose a file system, and that choice decides which operating systems can read and write it, how large individual files can be and which security features, such as permissions and encryption, are available. Choosing the wrong one is behind many 'why can't I copy this file' tickets.
NTFS (New Technology File System) is the standard for Windows system drives. It supports file and folder permissions, encryption with EFS (Encrypting File System), compression, disk quotas and journaling, which records pending changes so the volume can recover cleanly after a crash or power loss. Its file and volume size limits are so large that they never matter for normal work. macOS can read NTFS but cannot write to it by default, and Linux support varies by distribution, so NTFS is a poor choice for a drive that must be shared with a Mac.
ReFS (Resilient File System) is a newer Microsoft file system designed for data integrity and very large volumes. It uses checksums to detect corruption and can repair damaged data automatically when paired with Storage Spaces mirroring. It is aimed at servers, storage pools and virtual machine storage, and it lacks some NTFS features, so you do not normally install Windows onto it. Think of ReFS as the choice for resilient data storage rather than for a boot drive.
FAT32 (File Allocation Table, 32-bit) is old, simple and readable by almost everything: Windows, macOS, Linux, cameras, game consoles and car stereos. Its famous limit is a maximum file size of 4 GB (minus one byte), and Windows's built-in graphical formatting tools have traditionally offered FAT32 only for volumes up to 32 GB. It has no permissions and no journaling. exFAT (Extended FAT) was created for flash media: it removes the 4 GB file limit, supports very large volumes and is readable and writable by modern Windows and macOS, which makes it the usual choice for large USB drives and SD cards shared between those systems. Like FAT32, it has no permissions or journaling.
The other operating systems have their own defaults. On Linux, ext4 (fourth extended file system) is the common default; it is journaled and supports Linux permissions and large files. XFS is a high-performance journaled file system, the default on Red Hat Enterprise Linux and its relatives, and is well suited to large files and parallel workloads. Windows cannot read either natively. APFS (Apple File System) is the default for macOS, iOS and iPadOS. It is optimized for SSDs and supports snapshots, space sharing between volumes in one container and strong built-in encryption. Older Macs used HFS+ (Mac OS Extended). Windows cannot read APFS without third-party tools.
Consider a worked example. A video editor tries to copy a 12 GB project file from a Windows PC to a brand-new 128 GB USB drive and gets 'The file is too large for the destination file system', even though the drive is empty. You check the drive's properties and see FAT32. Because the editor also uses a Mac at home, NTFS would be awkward, since the Mac could read but not write it. You back up anything on the drive, reformat it as exFAT, and the copy succeeds on both computers. Formatting erases the drive, so always copy data off first.
Common mistakes: thinking 'file too large' means the drive is full (it usually means FAT32's per-file limit); choosing NTFS for a drive that a Mac must write to; assuming exFAT has permissions or journaling like NTFS; and expecting Windows to open an ext4 or APFS drive without extra software. Remember too that the 32 GB figure is a limit of Windows's formatting tools for FAT32, while the 4 GB figure is a limit of the file system itself.
Exam questions match the file system to the job, so learn the pairs. Windows boot drive or need for permissions and EFS: NTFS. Large-file flash drive shared between Windows and Mac: exFAT. Maximum compatibility with old devices and small files: FAT32. Linux server: ext4 or XFS. Mac or iPhone: APFS. Resilient Windows storage pool with automatic integrity checking: ReFS. Clue words such as 'journaling', 'permissions', 'checksums', 'snapshots' and '4 GB' point straight at the answer.
Key terms
- File system
- The structure an operating system uses to name, store, locate and protect files on a volume.
- NTFS
- The Windows default file system, with permissions, EFS encryption, compression, quotas and journaling.
- ReFS
- Microsoft's Resilient File System, which uses checksums and self-repair for large, integrity-focused storage.
- FAT32
- A widely compatible legacy file system with a 4 GB maximum file size and no permissions.
- exFAT
- A flash-oriented file system without FAT32's 4 GB file limit, readable and writable by Windows and macOS.
- ext4 and XFS
- Journaled Linux file systems; ext4 is a common default and XFS is the Red Hat default for high performance.
- APFS
- Apple File System, the SSD-optimized default for macOS, iOS and iPadOS with snapshots and encryption.
- Journaling
- Recording pending changes in a log so a file system can recover consistently after a crash.
A photographer's camera card, formatted FAT32, stops recording long 4K video clips at the same point every time. The camera splits or stops files at 4 GB. Switching to a card formatted exFAT, which the camera supports, lets it record long single clips that her Windows laptop and Mac can both open.
Check yourself
Which file system should you choose for a USB drive that must carry 10 GB files between Windows and macOS?
exFAT, because it removes FAT32's 4 GB file limit and both operating systems can read and write it.
Which Windows file system supports EFS encryption and NTFS permissions on a boot drive?
NTFS, the standard Windows system drive file system.
What is the default file system on current Macs and iPhones?
APFS, the Apple File System, which is optimized for SSDs and supports snapshots and encryption.
What feature helps a file system recover cleanly after a sudden power loss?
Journaling, which logs pending changes so the volume can be brought back to a consistent state.