File systems: NTFS, FAT32, exFAT, APFS and ext4, and choosing between them

Why this matters

File system questions look like a memory test — which one has a 4 GB limit, which one supports permissions — and behind each fact is a decision somebody has to make about a real disk. Formatting a drive the wrong way is not fatal, but it is discovered at the worst moment: when a 6 GB file will not copy, or when a drive will not mount on the machine it was bought for.

The way to hold this objective is as a short list of capabilities, and then a short list of which systems have them. Almost every exam question is asking which capability the scenario needs.

The lesson

What a file system actually provides beyond somewhere to put bytes

A file system is the structure that turns a partition into something you can name, find and share things in. What it provides, beyond storage:

• Names and hierarchy, with rules about length, allowed characters and case sensitivity that differ between systems and cause real problems when files move between them.
• Metadata — timestamps, attributes, and on some systems extended attributes and alternate streams.
• Permissions, which is the biggest single dividing line: some file systems can record who may do what, and some cannot record anything at all.
• Reliability features. Journaling records an intended change before making it, so an interrupted write leaves a recoverable state rather than a corrupt one. This is why an NTFS volume survives a power cut that would leave a FAT32 volume damaged.
• Limits — maximum file size, maximum volume size, maximum path length.
• Extras — compression, encryption, snapshots, deduplication, quotas.

The consequence that matters most in practice: a file system without permissions cannot protect anything. Copying a file from an NTFS volume to a FAT32 memory stick discards its permissions entirely, because there is nowhere to put them. That is a one-line answer to a whole family of exam questions and it is also a genuine data-protection problem.

NTFS: permissions, journaling, compression, encryption and size limits

NTFS is the default for Windows system volumes and there is no good reason to use anything else for one.

What it provides:

• Permissions — per-file and per-folder access control, with inheritance. This is the foundation the security objective builds on.
• Journaling, so an interrupted write is recoverable.
• Compression per file or folder, which trades processor time for space and is rarely worth enabling today.
• Encryption — the Encrypting File System, which encrypts individual files against a user's certificate. Distinct from BitLocker, which encrypts the whole volume, and much easier to lose access to.
• Shadow copies, which is what restore points and "previous versions" are built on.
• Quotas, limiting how much space a user may consume.
• Limits large enough to be irrelevant in practice — volumes and files far beyond any disk you will meet.

Two practical notes. Permissions travel with a file within an NTFS volume when it is moved, and are inherited fresh from the destination when it is copied — a distinction with real consequences that returns in the permissions lesson. And NTFS is readable by macOS and most Linux systems but writable only with additional software on macOS, which matters when choosing a format for a shared external disk.

FAT32 and exFAT: the limits that decide which removable disk gets which

These two exist for removable media, and the choice between them is decided by one number.

FAT32:

• Maximum file size 4 GB. This is the limit that decides everything. A single video file, a disk image, or a large archive will not fit.
• Maximum volume size of 32 GB when formatted by Windows' own tool, though larger volumes exist and work.
• No permissions, no journaling.
• Read and write by essentially every device ever made — cameras, car stereos, televisions, games consoles, firmware update routines.

exFAT:

• No practical file size limit.
• No permissions, no journaling.
• Read and write by Windows, macOS and modern Linux, and by most but not all consumer devices.

So the rule: exFAT for anything that will carry large files between computers; FAT32 only when a device demands it. The typical FAT32 case is a firmware update stick, a car, or an older camera — and UEFI's EFI system partition, which is FAT32 by specification.

The shared weakness is worth stating: neither journals, so both are vulnerable to corruption when a drive is removed during a write. "Safely remove hardware" is not superstition on these file systems; it is the flush that makes the volume consistent.

APFS and ext4, and the cross-platform problem they create

APFS is Apple's current file system. It is optimised for solid-state storage, it supports snapshots and cloning cheaply, it encrypts natively, and it replaced the older HFS+ on every current Mac. macOS also still reads HFS+, which is what you will find on older external disks.

ext4 is the common Linux default. It journals, it supports permissions and ownership in the Unix model, and it is entirely unremarkable in the best sense. Other Linux file systems exist and are chosen for specific reasons; ext4 is what you will meet.

The cross-platform problem is the examinable part, and it is simply stated: each platform's native file system is poorly supported by the others.

• Windows does not read APFS or ext4 without additional software.
• macOS reads NTFS but does not write it without additional software.
• Linux reads and writes NTFS well and reads APFS poorly.

Which means an external disk shared between platforms should be exFAT, accepting that it has no permissions and no journal, or the sharing should happen over the network rather than by carrying a disk around.

And the practical support consequence: a disk that a machine "cannot see" is often a perfectly healthy disk formatted for another platform. Offering to format it is the wrong answer, and reading it on the platform that owns it is the right one.

Choosing a file system from the requirement rather than from habit

The method is to start from the requirement, in this order:

1. Will this hold an operating system? Then it is that system's native file system — NTFS for Windows, APFS for macOS, ext4 for Linux. There is no decision to make.
2. Does it need permissions? Only NTFS, APFS and ext4 have them. If the answer is yes, a FAT variant is excluded immediately.
3. Will a single file exceed 4 GB? Then not FAT32.
4. Which devices must read it? A device that only understands FAT32 decides the answer by itself.
5. Is it shared between platforms? exFAT, unless every platform involved can write the alternative.

Worked through. "An external disk for transferring project files between a Windows workstation and a Mac, including video files of several gigabytes." Not a system disk, no permissions needed, files over 4 GB, both platforms must write it → exFAT.

"A USB stick for a motherboard firmware update." The firmware decides → FAT32, because that is what firmware reads.

"A second internal drive on a Windows machine holding departmental files." System platform is Windows, permissions are needed → NTFS.

The habit worth building is to say which requirement forced the answer. "exFAT" is a guess; "exFAT, because a Mac has to write it and the files are over 4 GB" is a decision, and the second one is what the exam is scoring.