Big Drives. Big Files. Big Problems.

The first hard drive I purchased, way back in the 1980s, held 10 MB . That's about enough space to hold two mp3 music files. Paltry doesn't even begin to describe that size of hard drive. Today it's hard to find a new hard drive that's smaller than 1TB . That's enough space for 200,000 mp3 music files.

What's driving this insane increase in size? Well, more and larger files of course. Today it's not uncommon to have files that are much larger than 1GB on your hard drive. And that brings us to the challenge that this column will address.

Computer hard drives are not just one big block of space. They look like that to you in Windows Explorer or in Finder, but in fact they are broken up into different pieces. This is a very technical subject so we're going to gloss over a bunch of stuff here, but for the purposes of this discussion just understand that your hard drive actually acts like a big wall of post office boxes. When you read a file off the hard drive, it is looked up by the post office box number that it was written to. And when the file is larger than one post office box, it is stored in a bunch of post office boxes. Here comes the problem. There is a limit to the number of post office boxes that your operating system can handle. And there is another limit: the number of post office boxes that your file can take up.

One of the oldest file systems around is called FAT . The FAT file system has several versions, but the two you're most likely to run into these days are: FAT 16, limited to a maximum hard drive size of 2GB and maximum file size of 2GB; and FAT 32, limited to a maximum file size of 4GB and a maximum hard drive size of 8TB .

That's not the whole story of course. There's another player here and that's your computer's BIOS. This is the firmware that boots up your computer, and deals with the interface between various components in your computer, including the hard drive(s). It's most likely limited to 2TB for a hard drive. So, before you buy a hard drive larger than 2TB make sure your BIOS can support it. Your sales person should be able to confirm this.

Not so very long ago these limits seemed, well, almost limitless. But 3TB drives are on sale and larger will come. And right now, if you try to rip a DVD you own to your hard drive, it may not fit. That's because it will almost certainly be larger than 4GB.

If you try to copy a file larger than 4GB to a drive and it tells you that there isn't enough space, even though you know that there's more than that free, it's likely that it's because the drive is formatted as FAT. The solution is to reformat the drive to NTFS. NTFS is Window's current file system. It supports file sizes and hard drives up to 16EB .

You can usually do this without losing data. There's even an eHow page on it .

Unless you're on an older Mac you probably won't face this in Apple land, unless of course you have an external drive that you previously/currently used on a PC. In that case you'll want to reformat it to HFS+, Apple's equivalent to NTFS. You can do this with Disk Utility. Just remember once it's in Apple format you can no longer read it with a PC.

So, watch out for gigantic files that give strange copying errors and get ready to buy a new computer if you suddenly feel the urge to buy a hard drive larger than 2TB.

Happy Computing.

1. MB is megabyte or 1 million bytes. Interestingly (for computer geeks) when talking about RAM memory a megabyte means 1,048,576 (1024*1024), but for physical media like hard drives it means 1,000,000.
2. A typical mp3 music file is around 5 MB.
3. TB is terabyte or 1,000,000,000,000 bytes. Put another way a million megabytes.
4. GB is gigabyte or 1,000,000,000 bytes.
5. FAT stands for File Allocation Table.
6. Of course it's not that simple. Different versions of Windows have their own limits, but let's go with this as a theoretical limit.
7. Firmware is permanent code. As opposed to software, which can be written over.
8. EB is exabyte or 1 with 18 zeroes after it.
9. http://tinyurl.com/22w6cmo