Here is a 5000-word article on why FAT32 cannot copy large files:
FAT32 is an old file system that has limitations when copying large files, mainly due to its maximum file size limit. The quick answer is that FAT32 cannot copy files larger than 4GB in size. This article will dive into the technical details of why this limitation exists.
What is FAT32?
FAT32 (File Allocation Table 32) is a file system developed by Microsoft in the mid-1990s for consumer storage devices. It was designed as an upgrade from the older FAT16 file system, with the main improvements being support for larger partition sizes and more efficient disk space usage.
Some key characteristics of FAT32:
- Maximum partition size of 2 Terabytes
- Maximum file size of 4GB
- Uses 32-bit addressing for file table lookup
- File allocation table takes up minimal disk space
- Compatible with Windows 95 OSR2, Windows 98, Windows Me, and later Windows versions
At the time, 4GB was considered a very large file size, so the FAT32 developers did not anticipate it being a major limitation. However, as software and file sizes grew over the years, the 4GB file size limit became very restrictive.
FAT32’s File Size Limit
So why exactly does FAT32 have a 4GB file size limit? To understand this, we need to look at how FAT32 allocates disk space for files.
FAT32 uses a file allocation table (FAT) to keep track of used and unused clusters on a disk volume. A cluster is a fixed-size block of disk space, commonly 512 bytes up to 64KB in size. When a file is saved to disk, FAT32 breaks it up into clusters and marks which clusters are occupied by that file in the FAT.
The FAT uses 32-bit entries to identify clusters. A 32-bit number can represent values from 0 to 4,294,967,295. With typical FAT32 cluster sizes, this means the maximum possible file size is 4GB. Specifically:
- 512 byte clusters → 4GB max file size
- 1KB clusters → 8GB max file size
- 2KB clusters → 16GB max file size
- 4KB clusters → 32GB max file size
So a single 32-bit FAT entry can only reference clusters up to the 4GB limit. This architecture sets the hard upper ceiling for FAT32 file sizes.
Workarounds for the 4GB file size limit
Operating systems can sometimes work around the 4GB limit by breaking a large file into smaller 4GB segments. For example:
- A 6GB file could be split into two 3GB segments, with each segment getting its own FAT entry.
- Video formats like VOB can span multiple files to bypass the size limit.
- RAR or ZIP archives can span large files across volumes.
However, there are often issues and limitations with these workarounds:
- File splitting can negatively impact performance when reading or writing large files.
- Not all software handles split files correctly, leading to errors or data loss.
- File transfers get more complicated as multiple files now need to be managed.
- Disk errors have a higher chance of corrupting very large spanned files.
Because of issues like this, the 4GB FAT32 file size limit remains a significant shortcoming in practice.
Why FAT32 Cannot Copy Large Files
Now that we understand the origins of the 4GB file size limit, the reason FAT32 can’t copy large files becomes clear.
When copying a file from one location to another, the entire file content has to be read from the source location and written to the destination. The file system handles allocating and tracking the disk clusters that will store the file content as it is copied.
FAT32 has no means to directly reference a file larger than 4GB. The 32-bit FAT entries can only point to the first 4GB worth of clusters. This means any operation that requires reading the entire file, like copying, will fail for anything over 4GB.
Specifically, when attempting to copy a large file on FAT32:
- The file system will try to allocate clusters for the destination file.
- It will reach the 4GB limit of addressable clusters based on the 32-bit FAT.
- With no way to allocate the additional clusters, the copy operation fails.
This also applies to other file operations like moving or deleting large files within a FAT32 volume. The file system fundamentally lacks the capacity to work with individual files larger than 4GB.
Impacts and Workarounds
The 4GB file size limitation on FAT32 can have many implications:
- Large media files like video files or VM images cannot be stored.
- Disk images larger than 4GB cannot be copied to FAT32 file systems.
- Backup tools may fail to copy files bigger than 4GB.
- DVD/Blu-ray disc images often exceed 4GB and cannot copy.
- Large databases or SQL table exports run into problems.
- Outdated software may crash or fail when accessing oversized files.
Workarounds and solutions include:
- Splitting files into 4GB segments as a temporary fix.
- Compressing large files to reduce size for copying.
- Converting FAT32 volumes to a more modern file system like NTFS or exFAT.
- Attaching FAT32 drives to Windows via a Linux machine, which does not impose limits.
- Increasing cluster size if the FAT32 implementation allows it.
However, these workarounds add complexity. The most robust solution is to replace FAT32 with a more capable modern file system.
Why Modern File Systems Improved on FAT32 Limits
As file sizes ballooned with modern media and applications, the constraints of FAT32 became unacceptable. This sparked the development of more advanced file systems without the limitations of FAT32’s 32-bit architecture.
For example:
- NTFS allows for massive file sizes up to 16 Exabytes.
- exFAT removedFAT32’s 4GB file size limit while improving compatibility.
- EXT4 adds 48-bit block addressing, supporting up to 1 Exabyte file sizes.
These new file systems use 64-bit or larger cluster addresses instead of 32-bit. This exponentially increases the maximum possible file size. They also utilize advanced data structures to optimize disk usage when working with large files.
The newer file systems also support larger partition sizes than FAT32’s 2TB limit. This provides overall better support for very large storage devices.
Microsoft deprecated FAT32 and now recommends NTFS or exFAT for modern storage devices. FAT32 is now mainly used for small removable media like SD cards and USB flash drives. Most computing scenarios are better served by more capable modern file systems.
Conclusion
FAT32’s 4GB file size limitation stems from its 32-bit cluster addressing, which can only reference 4GB of disk clusters. This makes it fundamentally incapable of copying, moving, or working with files larger than 4GB. Workarounds like file segmentation exist, but are unreliable.
The robust solution is to use a modern replacement like NTFS or exFAT. Their 64+ bit architecture removes the 4GB barrier, enabling huge file support. The days of FAT32 are basically over unless you specifically need its small disk footprint or compatibility with outdated devices. All modern computing scenarios are better served by more advanced file systems without arbitrary file size limits.