Understanding file systems and drive formatting

Your computer, phone or tablet can store a huge number of files, but how does it keep track of all of them? That’s where a file system comes in. It’s the system your device relies on to organise and manage data so it’s easy to find and use.

If you use a USB flash drive, an SD or a microSD card, or an external or a portable SSD, picking the right file system matters. It affects what devices can read your files, how big your files can be and even how secure your data is. In this guide, we’ll walk through the most common file systems and give you tips for choosing the right one for your storage needs.

What is a file system?

At its core, a file system is just a way for your computer or mobile device to organise and keep track of all the data you store on it. Without it, everything would be scattered randomly, making it almost impossible to find what you need.

Think of it like a digital filing cabinet. A file system defines how data is stored, accessed and organised on your storage device. It creates the structure that tells your device, “This is where the file lives, and this is how to get it when you need it”. In other words, file systems are the invisible organisers working behind the scenes, making sure your digital life stays neat and accessible.

Common file systems explained

Not all file systems are the same, and knowing the differences can save you from compatibility issues or storage limits. Let’s break down the most common ones that you’ll run into:

• FAT (File Allocation Table), FAT16, FAT32
  FAT is one of the oldest and simplest file systems, originally developed for MS-DOS. FAT32 is the most widely compatible version, which means it just works on almost anything. Its limitations include a 4GB file size maximum, susceptibility to fragmentation and the absence of modern features like file permissions, journalling, encryption and compression. It also restricts volume name characters. Even with these drawbacks, FAT32 remains handy for smaller USB drives and SD cards.
• exFAT (Extended File Allocation Table)
  Introduced by Microsoft in 2006, exFAT is basically FAT32’s modern upgrade for today’s storage needs. It handles huge files and big partitions, uses disk space efficiently and works across Windows and macOS. While exFAT boosts performance and cross-platform support, it still lacks advanced features like file-level permissions, journalling and encryption, and it can fragment over time.
• NTFS (New Technology File System)
  Launched in 1993 with Windows NT, NTFS is a robust, feature-packed system. It supports large files and partitions, file-level permissions, encryption, compression, journalling and SSD TRIM operations. While NTFS is reliable and secure, it can fragment over time, disk repairs may be slow and compatibility outside Windows is limited.
• APFS (Apple File System)
  APFS, introduced by Apple in 2017, is designed for modern Mac and iOS devices, especially SSDs. It offers features like cloning, file-level encryption, copy-on-write, space sharing and metadata optimisations, boosting performance and data integrity. Its limitations include restricted Windows compatibility and incomplete support from older third-party software.
• HFS, HFS+ (Hierarchical File System)
  HFS, introduced in 1986, and HFS+ (1998) were Apple’s go-to file systems before APFS. They organise data hierarchically using metadata and resource forks. These systems lack modern features like journalling, encryption and compression, have file and partition size limits, and can lose resource fork data when files move across systems.
• Ext4 (Fourth Extended File System)
  Ext4, introduced in 2008, is a widely used Linux file system and the successor to Ext3. It supports large files and partitions, uses journalling for faster recovery after crashes and is known for reliability and scalability. It can still fragment over time, and extremely large storage setups might push it beyond its design limits.
• ReFS (Resilient File System)
  ReFS is Microsoft’s newer file system designed for data protection and reliability, but it is mainly used in Windows Server and enterprise environments and is not intended for everyday consumer storage or USB flash drives.

Understanding these common file systems helps you pick the right one for your devices, keeping your storage organised and reliable.

Choosing the right file system for your needs

Selecting the right file system comes down to how you plan to use your storage. Device compatibility is the first consideration. FAT32 works almost everywhere, exFAT works across multiple platforms and NTFS is ideal for Windows-only setups, while APFS is ideal for modern Mac systems.

File size matters too. FAT32 cannot handle files larger than 4GB, so exFAT or NTFS is a better choice for videos or large backups. Security and advanced features are another factor. NTFS and APFS provide encryption and file permissions, which are especially important if you are using an encrypted USB to store sensitive data.

File system use cases for USB drives, SSDs and SD cards

How you use your storage drives plays a big role in picking the right file system. Different types of storage, USB drives, memory cards and SSDs, have different needs, and certain file systems are better suited to each scenario.

• FAT, FAT16 and FAT32 are some of the oldest file systems, but they still have their place. For USB drives, SD and microSD cards that are 32GB or smaller, FAT32 is usually the default choice. It works with most devices like cameras, phones or dashcams, though for SD and microSD cards it’s often best to format them directly on your device rather than on your computer. For SSDs, FAT formats are very rare today, only relevant for retro setups like a Windows 95 machine that requires special drivers.
• exFAT is a versatile option that works well across both Mac and Windows. For USB drives 64GB and larger, exFAT is ideal because it avoids the 4GB file size limit of FAT32. External or portable SSDs that need to work on multiple systems also benefit from exFAT’s cross-platform compatibility. Many SD cards 64GB and larger come pre-formatted in exFAT, which is perfect for cameras, dashcams or mobile devices that record long videos. But again, formatting your memory card directly on the device is usually the safest approach.
• NTFS is mostly a Windows-focused file system. It’s required for Windows PC boot drives, as well as bootable USB or external SSD drives, because Windows system files and boot loaders require it. It also works well for storing data backups on USB drives and SSDs for Windows. However, if you need to use your external storage on multiple platforms, NTFS is not recommended, since macOS can’t write to them without third-party software. For SD or microSD cards, there’s very little practical use.
• APFS is optimised for modern Mac systems, particularly SSDs used as boot drives on macOS 10.13 and later. It’s fast and secure, but not ideal for portable drives like USBs, external SSDs, SD or microSD cards, since Windows, Linux and most cameras can’t read it.
• Similarly, HFS+ is an older Mac file system used for boot drives on macOS versions 8.1 through 10.12. However, it is not recommended for use with USB drives outside of retro computing. There are no devices that use memory cards that will recognise this format. Drives using HFS+ can still be read by and written to using macOS, all the way up to macOS Tahoe 26, but support could eventually be dropped.
• Finally, EXT4 is mostly relevant for Linux users. It can serve as a boot drive for Linux SSDs, but it isn’t compatible with Windows, Mac or typical cameras and USB drives, so it’s rarely used outside Linux setups.

The key is to match the file system to your devices and the type of files you use most. That way, your drives work smoothly and avoid common issues like incompatibility or storage limits.

Formatting USB flash drives and SSDs

Formatting a drive might sound intimidating, but it’s really just the process of setting up a file system so your device can store and read files properly. The right file system makes sure your files are accessible and compatible with your devices.

Whether you’re formatting your USB drive for sharing photos and videos, or formatting your external SSD for backups, taking a little time to pick the right file system and complete the format carefully keeps everything running smoothly and helps prevent problems down the line. The file system you choose depends mostly on the operating system of the computer you will be using the drives with, as explained in our list of file systems mentioned above.