Why Can't I Copy a Large File Despite Having Larger Free Space?

In these days of extra large hard disks many try to copy large files from a DVD but find that can't even though there is plenty of free space on the hard disk. Why not?

The most likely cause for this is not some sort of copy protection but that the file being copied is too large for the file system to handle. Windows XP allows you to format a hard disk in two different file system formats: FAT32 and NTFS. These file systems differ in the size of file they can handle. FAT32, for example, can only handle files up to 4GB in size. When it was developed, that size file was almost unheard of but now, a DVD can have files that large or large routinely. So, if you are trying to copy a movie from a DVD onto your FAT32-formatted hard drive it likely won't copy as most full-length movies are files larger than 4GB.

FAT32

The original File Allocation Table (FAT) file system was introduced in 1977 and generally applied to floppy disk storage. It was later modified to work with hard disks and other removable media. FAT had a problem however; it could only manage spaces up to 2GB in size. As Windows came into being and programs became larger, the 2GB barrier became a serious problem. Thus, in 1996, with the OEM Service Release 2 (OSR2) of Windows 95 (also known as Windows 95b) came a FAT enhancement known as FAT32.

The two major features of FAT32 that improved upon the original FAT (or FAT16 as it's sometimes known) are the disk efficiency and size of the disk supported.

Files are stored in clusters on the disk. The size of the clusters depends on the size of disk. Under FAT, drives over 1.2GB used clusters that were 32K in size as the file allocation table itself could not track more clusters because of it's 16-bit structure. The 32-bit structure in FAT32 allows disks of that size to use 4K per sector. This improves efficiency as a file, no matter how small, will always use at least one cluster and the space in the cluster not used is wasted. FAT32 doesn't start to use 32K clusters until the disk goes over 60GB in size and can handle disks up to 2TB (terabyte or trillion bytes); though not all operating systems can deal with disks that size even if the file system can.

There are many other features changed between the two but these are the major ones to be concerned with.

The problem that many encounter now is one of the limits of FAT32 that's being run into: file size. The original FAT (FAT12) had a maximum file size of 32MB, FAT16 has a maximum file size of 2GB, and despite the much larger hard disk size supported by FAT32, the maximum file size only doubled to 4GB.

This is largely why a movie file larger than 4GB in size might not be able to be copied to a hard disk with lots of space. The hard disk is probably formatted using FAT32. There is no quick solution short of converting the hard disk to the NTFS file system.

NTFS

The New Technology File System (NTFS) was introduced in Windows NT (mid-1993) and is available in different forms in all following products: Windows 2000, Windows XP, and Windows Server 2003. It replaces FAT and FAT32 although some operating systems allow you to format disks as either FAT32 or NTFS. You can convert FAT32 disks to NTFS with little problem however going back from NTFS to FAT32 may not be possible due to FAT32 limitations that NTFS does away with (e.g., file size as seen above).

NTFS makes a number of improvements over FAT-based file systems. It uses advanced data structures, has a B+ tree directory structure, has improved reliability and use of disk space, allows for extensions such as security control, and has both a hard disk and file size of 16 EiB (EiB = exbibyte; a contraction of exa binary byte, and equaling 1,152,921,504,606,846,976 bytes).

So, if you need to copy files larger than 4GB, you need to make certain that the file system on the hard disk you are copying to is NTFS and not FAT32.

More Information

• Microsoft Description of FAT32
• How to convert a FAT16 volume or a FAT32 volume to an NTFS file system
• FAT32 Structure Information
• Wikipedia FAT Entry
• Wikipedia NTFS Entry