When Good Drives Go Bad

You've heard about them. I' you're lucky you've never experienced one. I'm talking about a hard drive crash. People are always asking my "how did my hard drive crash? It was working just fine yesterday?" Let's take a look at just what it is that makes a hard drive such a tough - yet delicate - piece of engineering wonder.

First let's make sure we're all on the same page here. Some people mistakenly call the box all the wires plug into a hard drive. Actually, the hard drive is just one of the pieces that's in that box. Next to the main processor it is by far one of the most critical components in your computer. It's is where Windows lives; it's where your pictures from your last vacation live; it's where everything you hold dear lives. If you don't have a backup of these important little items, you could be in for a really bad day when this thing finally fails.

Let's take a look at how these are built. This is pretty a generic description, but it fits most drives. The fundamental part of the drive - the part where your address book and Uncle Sid's pictures are stored is called a platter. As the name implies it is a round piece of magnetic material.

(Here's a quick bunny trail - little spots on this magnetic material can be given a positive or negative charge. Think of it as zeros and ones. On or off. These are called bits. And 8 bits add up to a byte. And it modern drives are approaching the capacity to store a terabyte - that's a thousand billion bytes. Think of it this way: you would have to cut down 50,000 tress and turn them into paper and then print them out to equal a terabyte of text stored on a hard drive.)

OK, back on track. Each drive has several platters stacked on top of each other with a little bit of space between each platter (see diagram). These platters are attached to a spindle that spins at 7200 RPM - that's faster than the crankshaft of an Indy race car.

In the space between these platter metal read-write heads fit with a clearance of less than the width of a human hair. These heads are like a phonograph needle that not only plays the music but writes it as well.

Now, let's get to the really fun part. You're probably wondering how those heads can find data to read or spaces to write. Well, there's a little part of the disk that's reserved for what's called a File Allocation Table (FAT). This tells the read/write heads where to read or write the data you are working with. Since the computer doesn't know how big that letter to Aunt Sally is when you click "Save' part of it may be written in one spot on one platter and the rest on a completely different part of a completely different platter. The only way to decode the location of all the parts of your letter is locked in the FAT. Hold that thought - we'll come back to it in a minute.

Let's look at another critical area of your disk. It's called the Master Boot Record (MBR). It's like the FAT, only - as its name implies - it tells the computer how to boot up. It tells it where the information on Windows is along with all the information about the hardware attached to the system.

So you've got platters with a thin coating of magnetic material spinning at incredible speeds, and these platters are less than a hair's-breadth away from these solid metal read/write heads. Do you smell a recipe for disaster?

But wait, there's more. There is a tiny electric motor that spins the disk platters. It has to run at a very precise speed. This is because the address in the FAT is based on exactly where that read/write head was on the platter when it wrote those bits and bytes that belong to Aunt Sally's letter. And that position is based on the assumption that the disk was traveling at a precise speed when the data was written and that is is traveling at precisely the same speed when you want to read it. This is the key to the whole thing. If you data was written when the disk was spinning at 7,200 RPM and you try to read it when the disk is spinning at 7,000 RPM, you will be looking in the wrong place for your data. You will be reading gibberish! That's bad if it's your letter to Aunt Sally. But what if it's part of your MBR? That's right, your computer won't boot!

OK, now you know WHY hard drives crash - the system can't find the data where it thinks it should be. But HOW does that happen.

Well, one obvious reason would be if the disk platters wobbled for some reason - a bearing in the drive motor or spindle gets out of whack, or the computer takes a sharp whack (i.e. you kick it or drop it) then the platter(s) could be scratched, thus erasing any data that was there.

Besides wear and tear or taking a beating, what else can affect the rotation of the platters?

Some things you might not think of.

Power - if your power spikes or sags, it can affect the speed at which the platters are turning. Remember, it's an electric motor. More power = faster spin, less power = slower spin.

Unexpected shut down (power failure or turning the computer off without using the shutdown option) - this will interrupt the write process and mess up any or all of the items mentioned above.

The best advice I can give you is to back up your data regularly and purchase a battery backup. If you're not sure how to do either of these then PLEASE give us a call. We hate to be the ones to tell you your data is gone...