Why doesn't Mac hard drive need to defragment?

On Windows, traditional hard drives (not SSDs) often have to be fragmented - a process that takes a lot of time. On macOS (and Linux) you don't need to worry about this. Why?

What is fragmentation? Why does Windows need fragmentation?

First of all, remember that the fragmentation in question is with a spinning platter rather than an SSD (SSDs do not have a spinning disk and do not need fragmentation). Even on Windows, fragmentation is not as important as before.

New hard drives are faster, new machines have more memory, Windows also uses NTFS file system by default - all without having to defragment the hard drive. That's not to mention if you use those drives, Windows Vista, 7, 8 and 10 automatically defragment during maintenance.

What is defragmentation?

When deleting a file from a hard drive, the amount of space that the file occupies will be marked as usable. The more you delete, the more space you have in the hole. When the operating system writes a new file to the drive (and when the file size increases), part of it may be in this place, and part of it is elsewhere. That is called fragmentation.

Every operating system is more or less fragmented, but the way file systems handle this is important. macOS and Linux have slightly different ways to handle archives. Instead of placing multiple files close together, they will be scattered everywhere, thereby allowing space for larger files and creating new files. If fragmentation occurs, the OS will move the file around.

Windows is different. On old system files like FAT or FAT32, there is no protection against fragmentation and the drive must be defragmented regularly. Now, Windows defaults to using the file system as NTFS on multiple drives, despite its defragmentation capability (leaving room for file sizes to increase) but still not perfect.

Most flash drives are still FAT32 format and may be fragmented.

The defragmentation will fix by transferring the file, but this is very slow. Most users do not mind because Windows 10 automatically performs defragmentation but sometimes there are people who perform self-defragmentation.

Why doesn't Mac need defragmentation?

The simple answer is that it didn't encounter this problem from the beginning, because it uses a completely different file system. Plus, almost every Mac today uses SSDs and, just like on Windows, they don't need defragmentation.

The nature of the file system has caused Mac to not need to defragment

But even on older Macs using spinning drives, defragmentation is not necessary. It is due to how macOS stores files. HFS and APFS file systems that Mac uses automatically defragment files with a very good process called Hot File Adaptive Clustering.

When storing files on macOS, it will leave room for the file to expand instead of putting it all together. When opening the file, macOS can detect whether the file is in the wrong place and automatically switch to the right place. Combining these two processes makes you not defragment the drive, and Apple doesn't have to offer defragmentation tools on Mac.

What if I want to defragment on a Mac?

If you want, you can still do so but remember:

1. If the device is slow, it could be a cause.
2. There is no need to defragment on SSDs.
3. Not many software do this.
4. It may make the drive slower because it interferes with macOS's original defragmentation.

See more:

1. Use Disk Defragmenter in Windows
2. Top 5 hard drive defragmenters should be used
3. These quality hard drive defragmentation software