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When backing up large amounts of data the filesystem used on the backup media matters. FAT32 often can't handle the way that many backup programs work.

I have downloaded a backup program for Windows XP Home Edition. A differential backup of the C drive & System Settings to an external 250gb hard drive fails with a message that the drive is formatted as Fat 32 & the maximum backup is 4gb. There is plenty of space on the external drive. How do I backup 40 gigabytes?

Actually the clue is right there in the error message: the problem is FAT32.

Fortunately the solution is fairly straightforward.

FAT32 is what's called a "file system" which specifies exactly how files are laid out on a hard disk. By that I mean that it defines where the computer would go to look for the names of files and folders stored on the disk and how the computer locates the data on the hard disk associated with the files and folders that it finds.

FAT32 (which stands for "File Allocation Table, 32 bit version") is actually fairly old and was devised as a easily upwards compatible version of its predecessors FAT16 and FAT12. FAT12 actually dates back some 30 years.

"One of the limitations of FAT32 is simply this: a single file can be no greater than 1 byte short of 4 gigabytes."

One of the limitations of FAT32 is simply this: a single file can be no greater than 1 byte short of 4 gigabytes.

My guess is that your backup program is attempting to write its backup in to a single file, and as a result that file is exceeding that 4 gigabyte limit. Fortunately it's nice enough to point out the exact problem: that FAT32 is at the root of the problem.

Since you're using Windows XP, the solution is actually quite simple: convert the hard disks format from FAT32 to NTFS.

NTFS (for New Technology File System) was introduced with Windows NT in the early 1990's. Among other things it replaces the 4 gigabyte file size limit with 2 terrabytes or 2,048 gigabytes. That should be sufficient for your needs, as it's roughly 8 times bigger than your 250 gigabyte hard drive.

Converting your external drive to NTFS is simple. Open a Windows Command Prompt and enter the following command:


Be sure to replace "E:" with the actual drive letter that corresponds to your external drive.

The convert utility converts everything in place with no data loss. If you'd rather, you can also reformat your external hard drive to NTFS, but that will of course erase the contents of the drive in the process.

Once the external drive is formatted as NTFS your backup program should have no problems writing out that 40 gigabyte backup file.

Coincidentally, that's exactly what I have on my external hard drive.

Article C3213 - November 15, 2007 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

November 16, 2007 3:50 AM

So what will come after NTFS?
Files sizes are becoming so huge now (a Blue-ray movie is typically 45gb) and the size of Hard Drives getting bigger.
What happens when people want to back that much data up?

November 16, 2007 7:44 AM


I have a feeling that the 2TB limit won't be a problem for a couple years yet.
Supposedly Windows is releasing WFS (Windows File System). They stripped it from Vista, but it is supposed to get around that limitation (on the off chance it's a problem).

JFS, however, has a limit for the file size of 4 Petabytes (4000 TB). (according to wikipedia:


November 19, 2007 5:58 PM

Ziggie: actually, NTFS's theoretical maximum file size limit is 16 *exa*bytes, over 4000 times bigger than JFS's limit. It's only in the current implementation that you're limited to 16 (not 2) terabytes.

(Besides, it's not as if Microsoft might switch to JFS, as it's an inferior file system to NTFS in a number ways -- no file changelog, no internal snapshotting, doesn't support transparent compression, doesn't support filesystem encryption... etc.)

Steve Bukosky
December 29, 2008 5:04 PM

That answers why Acronis made around 36 files rather than one big one on my new external HD. That's one question answered! If Acronis mentions this in their software, I missed it.

June 23, 2009 8:27 AM

where is the command prompt?

[All] Programs -> Accessories -> Command Prompt.
- Leo

Ged McDonald
December 4, 2009 8:49 AM


I am running Windows XP & have bought an external hard drive to perform a full back up, the hard drive came with Nero BACKITUP software. The booklet states the external drive is formatted in FAT32 format. I have tried to use the Windows XP back up utilty, not Nero, and get the 4GB error message. I have tried to convert my external drive to NTFS as suggested by entering CONVERT F: /FS:NTFS but receive another message in DOS 'Enter Current volume label for drive F:' - am I missing something?


Not at all, you simply need to type in the current label for the external drive. This article talks about what that is, and how to create one if the drive is unlabelled: What's a Volume Name?

March 18, 2010 10:52 PM

EXCELLENT explanation on the file system issue.

I recently got a 16GB flash drive and I've been meaning to backup my VMWare Ubuntu image. I was going crazy since it wouldn't let me copy it over.
That line you mentioned:

worked like a charm! In about a minute the file
system was converted and I could backup the file.
GREAT explanation.

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