Computer hardware problems can range from being harmless to catastrophic. A hard disk failure is one of the most serious hardware problems. It’s something that cannot be taken lightly because the data on the disk could be lost forever depending on the severity of the damage. Hard disk failure can occur instantly without notice and other times it can happen over time. Usually there are warning signs when a hard disk is failing over time.

I’m going to show you some warnings signs that your hard disk may be on its way out. It’s always good practice to back up your data to secondary storage before your hard disk crashes.

Warning Sign #1: Clicking or tapping noise coming from the hard drive

A computer hardware problem is imminent if you start hearing a clicking or tapping noise coming from your hard drive especially when first turning on your pc or retrieving a file. This is a really bad sign that your hard drive is dying. When you hear such unusual noises you should immediately back up your data.

Warning Sign #2: Computer is running unusually slow

Hard disk failure is a possibility if your computer is running slow and the slowness cannot be resolved through general maintenance tasks. If you already tried the following: scanned for viruses, remove temporary files and unused programs, check for software problems, defragment your disk and your computer is still slow it’s possible that the hard drive is failing.

Warning Sign #3: Files mysteriously disappeared

If you are missing some files that you know for sure the files were there and nobody deleted them, it’s possible that your disk may have some bad sectors. Your missing files may be sitting on the bad sectors. When your disk has bad sectors this is a sure sign of malfunction.

source: http://ezinearticles.com/?Computer-Hardware-Problem—Top-3-Warning-Signs-of-Hard-Disk-Failure&id=5646495

Hard drives are destined to fail. It’s just a matter of when. As terrifying as its sounds, it’s true. It’s scary because your entire life can be on that drive in the form of valuable documents, pictures or other data. It’s important to backup and be prepared for this fact before you boot up the computer and get the dreaded No Operating System Found error. This can be a bad error or a really devastating error. The following will help you how to tell if your hard drive has died or whether there is another reason why it is not booting.

Hard Drive Problems

With the exception of new Solid State Drives (SSD), hard drives have a lot of moving parts. Because of this, there is a lot that can fail mechanically as the result of a manufacturing defect, heat, or simply normal wear and tear. If your hard drive has a physical problem, it has failed. You can take it to a business that specializes in recovering data, but it will probably cost you more than the computer’s worth to get that data back.

The hard drive can also fail due to electrical issues, and as with a mechanical problem, it will cost a lot to retrieve the data on the disk.

Lastly, the drive can simply be corrupt, which means it cannot boot but can be repaired by either reinstalling the Operating System or running a repair install from your Windows disk.

No Operating System Found

If you get the No Operating System Found error, this means the BIOS was in the process of handing boot control over to the hard drive and its Operating System but could not proceed because it could not locate an OS. The following could be some of the reasons for this error:

* There is a disk in the CD drive, floppy drive or USB port. Depending on how your BIOS is configured, it could be trying to boot to a drive other than the hard drive. Remove all disks and try booting up again. If Windows loads, go into the BIOS and specify the hard disk as the first boot device.
* The hard drive is unplugged. Open the case and confirm both the power connection and the data connections are securely attached.
* Jumpers are not configured properly. This problem will not just happen by itself. Unless you have been changing drive configurations or have recently added a new drive, this likely will not be the problem.
* Drive does not show up in BIOS. Change the power connector from the power supply, replace the data cable and perform other steps to determine why the drive is not recognized in BIOS. If the DVD drive shows up when you swap it out with the hard drive, this eliminates the motherboard controller and cables as being the problem. The next likely reason a drive does not show up in the BIOS is because it has died.

Fixing A Corrupt Hard Drive

You can quickly fix a corrupt hard drive if you have a Windows disk. If you have Windows XP, you can proceed to the Recovery Console by pressing the R key when prompted, then type chkdsk /r from the command prompt to repair Windows. Both Vista and Windows 7 have a Startup Repair option available when you boot to the Windows install disk. Windows Vista and Windows 7 will repair the drive automatically when you click the Startup Repair link.

In conclusion, to determine if your hard drive has died, the first place to look is the BIOS. If it’s not listed there–and if you have not performed any recent upgrades–then the hard drive has probably suffered a catastrophic failure. Also, pay close attention to your computer. If it begins making grinding sounds, if it crashes frequently, or if files suddenly begin disappearing, then this can be a sign of impending doom and you should take appropriate actions to replace it as soon as possible.

source: http://www.pctechbytes.com/hardware/hard-drive-has-died

Your hard drive contains all of your important data, like the Windows Operating System, pictures, music, and other data you do not want to lose. Keeping track of the health of your hdd is a dubious chore. Unfortunately, most people do not realize there is a problem before it’s too late and they lose all of their data.

You can spot early warning signs of imminent failure if your hard drive has SMART technology. SMART stands for Self-monitoring Analysis and Reporting Technology and will often give you a notice if the drive is experiencing problems. If you see a warning like that at boot, be sure to backup you data and buy a new drive.

Using Third Party Software to Monitor Your Drive

You can use applications that help keep an eye on your drive. HDD Health is one of those aplications. It can give you valuable info about the the disk’s temperature and overall health. It can also give you all of its SMART statistics.

It also shows valuable hdd information, such as the model number, partitions and remaining space.

But unless there is a glaring problem with the drive, there is no way to tell if it is about to fail. In fact, hard drives can fail suddenly and without warning. These tools should be used in addition to the SMART technology built into the drive.

How to Diagnose Problems With Your Hard Drive

Generally speaking, if you begin getting errors or blue screens that you cannot recover from, or if you occasionally cannot boot into Normal Mode or Safe Mode, then your hard drive might be on the way out. Problems will start intermittently and gradually grow worse. If you start experiencing these problems, you can try running chkdsk. Chkdsk will repair errors (if you specify that) and make sure data is no longer written to those areas of the disk. To run a chkdsk, right click the hard drive and select Properties. Under the Tools tab, click Check Now in the Error Checking area. A box will pop up. Choose Automatically Fix Errors and Scan for and attempt recovery of bad sectors. You will likely need to reboot before the check begins and it could take quite a while.

Make sure the size of the hard drive appears correctly in the BIOS and in My Computer. For instance, if the drive once reported it was 20 Gigs and now reports as 13 Gigs, there could be a problem.

Listen for strange noises from the hard drive. You have been using your PC for a long time, if the hard drive begins making scraping, churning or any other sounds out of the ordinary, then it could mean the drive’s actuator arm is damaged or perhaps the ball bearings on the spindle are starting to go.

source: http://www.pctechbytes.com/troubleshooting/hard-drive-troubleshooting-2

The hard drive is a device that is used for reading/writing digital data. It is a general section of every computer. The HDD keeps all the information we have. The hard drive might basically be separated into 2 general pieces – the mechanic one and the electronic one.

The mechanical part of the hard drive contains the following: plates, heads, spindle, arm and slider. The plates of the hard disk drive are produced from aluminum alloy or from glass. They are very smooth and are manufactured in special areas with no dust. In order to achieve the magnetic covering they are wrapped with cobalt alloy. On the plates is stored all the digital information.

The plates are being rotated with a very high speed by the spindle. It uses 12 volts. Ordinary hard disks (their plates) are rotating with a pace of 7200 RPM (revolutions per minute).

The plates have numberless very microscopic sectors which include a number of even tinyer bits of data – every bit is 0 or 1. When the digital data is being written or read the small bits are accessed by the also so tiny head. The head is being floated just above the correct bit by an arm and slider which are pretty precise. There are truly complex systems that command this operation and secure the accurate spot.

The read/write operation is very complicated. The most easy explanation is that the head and all the bits of information are magnets. When the head is right overhead a bit, and the data needs to be changed, the microscopic magnet bits shift their direction of their magnetic poles.

The electronic part is getting increasingly complicated with the years. It includes now a its own memory, separate processor and its own software. The electronics of the HDD manage the spinning of the spindle, the movement of the arm and the exact positioning, controlling the write/read process and even others.

The electronics also contain the HDD’s cache. This is chip of pretty fast memory that plays the role of a buffer between the information on the plates and the random access memory of the PC.

This is pretty much what the HDD is. There are also portable hard drives (also external hard drive) and they operate by the same rules. They just have divers interface for creating communication with the PC.

source: http://ezinearticles.com/?How-Does-the-Hard-Disk-Function?&id=5173215

When you replace a hard drive, what do you do with the old one? Most people give their surplus drives away to friends or charities. Some just throw them in the trash. But what about all the data on that old drive? Even if you deleted files or formatted the drive, your data might still be readable. Here’s how to securely and completely erase every last bit of data from your hard drive…

How to Erase Your Hard Drive

Erase Hard Drive What’s on that old hard drive? Your name, address, phone number, email, tax returns, bank account info, love letters… maybe some software or (ahem) other files you’d rather no one else knew you had. Maybe your family’s info is on there, as well. How can you erase all that stuff before disposing of the drive?

You might be surprised to learn that when you delete a file, it’s really not gone. All the “delete” command does is erase the record of a file’s location on the hard drive, stored in the Master File Table (MFT) or File Allocation Table (FAT). That’s like removing the cards from a library’s card catalog but leaving the books on the shelves for anyone to inspect at random.

Okay, but formatting a hard drive erases all data on it, right? The operating system warns you about that before it executes the format command. But no, you can even recover files from a freshly formatted drive if nothing has been written over them. Data recovery software such as the Data Recovery Wizard from EASEUS.com can easily restore files on a freshly formatted drive.

To truly make your sensitive data unreadable, you have to cover it completely with new data; not just once, but several times. It’s like using a pen to scratch out something you wrote earlier. A few penstrokes will obliterate old writing to the casual observer, but someone with a magnifying glass and determination can still make out the indentations of the old writing on the paper unless you scribble over it half a dozen times or more.
Tools to Securely Erase Files From a Hard Drive

Mac operating systems come with secure data erasure built in. All you need to do is move folders or files to the trash can and from the Finder menu select ‘Secure Empty Trash’. Windows does not have a secure data erasure function, but several third-party utilities provide this ability.

Eraser is a free utility for securely erasing data from a Windows hard drive. It works with Windws 95/98, XP, Windows Server 2003 and 2008, Vista, and Windows 7. Eraser has a simple name but it erases files completely in several complex ways.

The default erasure method used by Eraser and many other similar programs is called the Guttmann Method after its inventor, Dan Guttmann. It overwrites data 35 times, ensuring that no one will be able to recover it. Of course, that takes a very long time. Eraser and other utilities let you schedule a secure data erasure during hours when you won’t be using your computer.

A second, less thorough method is called the US DoD 5220-22.M Method. This is a standard developed by the U. S. military for securely erasing drives “good enough for government purposes.” It overwrites data seven times. That will thwart all but the most determined and well-equipped data recovery experts, but it won’t stop the “men in black” from the CIA, the National Security Agency, or those guys from CSI.

Years ago, I remember reading a story about one paranoid guy who lived in fear of the feds busting his door down and confiscating his computer. He had a strong electromagnet positioned near the computer, so that when the dreaded midnight raid occurred, he could flip a switch and instantly wipe the hard drives clean. I wouldn’t recommend that method, because forensic tests have shown that electromagnets can leave some data intact.

I’d like to mention one final method of completely erasing your hard drive, which I have personally found to be immensely satisfying. It involves physically removing the hard drive from the system unit, and beating it senseless with a 16-lb steel sledge hammer. There’s always the possibility of shrapnel, so place the drive in a brown paper grocery bag first, and wear eye protection. When you’re finished, you can inspect the carnage and maybe learn a little something about how hard drives work.

source: http://askbobrankin.com/completely_erase_a_hard_drive.html

This is actually technology that has been around for many years, but only now is it actually set to become something that consumer may actually get to use within the next year. This article takes a look at exactly what is a solid state drive and how it may benefit consumers, especially with their portable computing.

What is a Solid State Drive?

Solid state is an electrical term that refers to electronic circuitry that is built entirely out of semiconductors. The term was originally used to define those electronics such as a transistor radio that used semiconductors rather than vacuum tubes in its construction. Most all electronics that we have today are built around semiconductors and chips. In terms of a SSD, it refers to the fact that the primary storage medium is through semiconductors rather than a magnetic media such as a hard drive.

Now, you might say that this type of storage already exists in the form of flash memory drives that plug into the USB port. This is partially true as solid state drives and USB flash drives both use the same type of non-volatile memory chips that retain their information even when they have no power. The difference is in the form factor and capacity of the drives. While a flash drive is designed to be external to the computer system, an SSD is designed to reside inside the computer in place of a more traditional hard drive.

So how exactly do they do this? Well, an SSD on the outside looks almost no different than a traditional hard drive. This design is to allow the SSD drive to put in a notebook or desktop computer in place of a hard drive. To do this, it needs to have the standard dimension as a 1.8, 2.5 or 3.5-inch hard drive. It also will use either the ATA or SATA drive interfaces so that there is a compatible interface.

Why Use a Solid State Drive?

Solid state drives have several advantages over the magnetic hard drives. The majority of this comes from the fact that the drive does not have any moving parts. While a traditional drive has drive motors to spin up the magnetic platters and the drive heads, all the storage on a solid state drive is handled by flash memory chips. This provides three distinct advantages:

* Less Power Usage
* Faster Data Access
* Higher Reliability

The power usage is a key role for the use of solid state drives in portable computers. Because there is no power draw for the motors, the drive uses far less energy than the regular hard drive. Now, the industry has taken steps to address this with drive spin downs and the development of hybrid hard drives, but both of these still use more power. The solid state drive will consistently draw less power then the traditional and hybrid hard drive.

Faster data access will make a number of people happy. Since the drive doesn’t have to spin up the drive platter or move drive heads, the data can be read from the drive near instantly. In a recent demo of two similar equipped notebook computers, Fujitsu was able to demonstrate a roughly 20% speed increase in the booting of Windows XP on a SSD over a standard hard drive.

Reliability is also a key factor for portable drives. Hard drive platters are very fragile and sensitive materials. Even small jarring movements from an impact can cause the drive to be completely unreadable. Since the SSD stores all its data in memory chips, there are fewer moving parts to be damaged in any sort of impact.

Why Aren’t SSDs Used For All PCs?

As with most computer technologies, the primary limiting factor of using the solid state drives in notebook and desktop computers is cost. These drives have actually been available for some time now, but the cost of the drives is roughly the same as the entire notebook they could be installed into. This is gradually changing as the number of companies producing the drives and the capacity for producing the flash memory chips grows. Drives announced at the 2007 CES were priced at less than half of the drives of the same capacity from the previous year.

The other problem affecting the adoption of the solid state drives is capacity. Current hard drive technology can allow for over 200GB of data in a small 2.5-inch notebook hard drive. Most SSD drives announced at the 2007 CES show are of the 64GB capacity. This means that not only are the drives much more expensive than a traditional hard drive, they only hold a fraction of the data.

All of this is set to change soon though. Several companies that specialize in flash memory have announced upcoming products that look to push the capacities of the solid state drives to be closer to that of a normal hard drive but at even lower prices than the current SSDs. This will have a huge impact for notebook data storage.

source: http://compreviews.about.com/od/storage/a/SSD.htm

Introduction

Hard drive crashes are one of the most frustrating experiences one can have with a computer. The inability to read data off of the hard drive can render a computer useless. Even if the OS can run, the data may be inaccessible or damaged. The only way to recover from such a failure is to typically restore data from a backup onto a new drive with all the software installed from scratch. If no backup is available, then the data is either lost or will cost a lot for recovery services to retrieve.

This article is going to take a look at what causes hard drive failures, if failures are becoming more frequent and what steps one can take to try and avoid problems in the event of a failure.

Hard Drive Basics

Before understanding what can cause a failure, it is important to know the basics of how a hard drive functions. A hard drive is essentially a large device with magnetic storage media that is encased on rigid platters. This allows the drive to store large amounts of data that can be accessed and written to very quickly.

Every hard drive is comprised of several key components: case, drive motor, platters, drive heads and a logic board. The case provides protection for the drive in a sealed environment away from dust particles. The motor spins the drive up so the data can be read off of the platters. The platters hold the magnetic media that stores the actual data. The drive heads are used to read and write the data to the platters. Finally the logic board controls how the drive interfaces and talks to the rest of the computer system.

Common Drive Failures

The most common failure for a hard drive is something called a head crash. A head crash is any instance where the drive head manages to touch a platter. When this happens, the magnetic media will be etched off of the platter by the head and render both the data and the drive head inoperable. There is no clean recovery from such a failure.

Another common failure comes from imperfections on the magnetic media. Any time that a sector on the disk fails to properly hold the magnetic alignment will cause data to be inaccessible. Typically drives will have a few of these located on the platter, but they are marked out of use by a low level format from the manufacturer. Later low level formats can be done to mark sectors as unusable so they will not be used, but this is a long process that erases all data from the drive.

Mobile systems tended to be prone to platters that shattered. This was due to the fact that most hard drive platters are made of glass and were susceptible to shock. Most manufacturers have or are switching to other materials to prevent this from happening.

If there is electrical problems with the logic board, data on the drive can become unreadable or damaged. This is due to the logic board being unable to properly communicate between the computer system and the hard drive.

MTBF

In order for consumers to get a good idea of the lifespan of a hard drive, a drive was rated by something called MTBF. This term stands for Mean Time Between Failure and is used to represent the length of time that 50 percent of drives would fail before and 50 percent would fail after. It is used to give an idea to a buyer as to the average amount of time the device will function for. This was typically listed by the manufacturers on all computer drives but in recent years it has been removed from all consumer drives. They are still listed for enterprise class hard drives.

Capacity vs. Reliability

Hard drive sizes have been increasing dramatically over the last few years. This is due to the increase in the density of data being stored on the platters and the number of platters that are being placed inside of a hard drive case. For example, most drives used to feature two or maybe three platters, but many now can have up to four total platters. This increase in the number of parts and the reduction in space has greatly reduced the tolerances that the drives have and increases the amount of possible chance of failure.

Are Drives More Prone to Failure Now?

A lot of this has to do with the construction and use of hard drives. Most consumer computers were used only few a few hours per day. This meant that the drives did not have as long of continuous use that increase factors such as heat and movement that can lead to failures. Computers are much more prevalent in our lives and are being used for longer periods. This means that drives are likely failing more frequently due to heavier use. After all, a computer used twice as long as another will generally have a hard drive fail twice as quickly. So this hasn’t really increased the failure rate.

Of course, factors such as the increase in data density and number of platters may also be contributing the the chances of hard drive failure. The more parts and the tighter the density of the data on the platters means that there are more things that can potentially go wrong to cause data loss or a failure. To counter this though, technology has been improving. Better motors, chemical composition of the media and other materials means that failures that used to happen due to these parts are less likely to occur.

There is no hard evidence that failures are occurring more frequently. From my own personally experience, I have not seen an increase in the number of drives failing, but other people that I work with have seen a fair number of drives in their computers have problems. This is anecodotal evidence though.

Warranties may be a good indicator of how the industry is dealing with reliability. After the dark days surrounding the infamous Deskstar problems, many manufacturers were reducing warranties. Before this the typical warranty was three years in length, but many companies switched to one year warranties. Now companies are typically offering three to five year long warranties meaning that they must have confidence in their drives as they are costly to replace.

What to Do in Case of Drive Failure?

The biggest problem with a drive failure is the amount of data that can be lost. With the increase in the number of digital devices that we use and resulting data being stored on our computer systems, it is much more disruptive to our lives to have it destroyed. Data recover from damaged drives can range from several hundred dollars to several thousand. Data recovery services aren’t flawless either. A head crash will likely remove the magnetic media from the platter destroying the data forever.

There is no real way to prevent a drive failure either. Even the most reputable and reliable brand can have a drive that fails rapidly As a result, it is best to try and plan for an event that will cause the primary data drive to fail with data backups. There are a wide range of backup methods available to use. For some tips on this, check out the About Focus on PC Support Guide’s Data Backup articles.

One simple tip I like to suggest to people is portable hard drives. They are fairly inexpensive and due to their limited use, are less likely to fail when properly stored and handled. External hard drives are available in the exact same capacities as the desktop drives because they often use the same drives. The key is to only use the drive when backing up data or restoring it. This reduces the amount of time it is used and lessen the chance of failure.

Another option open to users is to build a desktop PC with a version of RAID that has data redundancy built in. The simplest form of RAID to setup is RAID 1 or mirroring. This requires a RAID controller and two identically sized hard drives. All data written to one drive is automatically mirrored to the other. In the event of a failure of one drive, the second drive will always have the data. For more information about RAID, check out my What is Raid article.

Conclusions

Hard drives in general are very reliable, but with the increasing amount that we use our computers to store the data from our lives, the more catastrophic it becomes to have that data be lost from a drive failure. In general the drives are not failing any faster than they have in the past, but with the increasing use of the drives, they are reaching their expected lifespan sooner. Because of this, it is important to be prepared for such an incident by planning how to store your data in multiple locations to avoid data loss.

source: http://compreviews.about.com/od/storage/a/HardDriveCrash.htm

Nearly every desktop computer and server in use today contains one or more hard-disk drives. Every mainframe and supercomputer is normally connected to hundreds of them. You can even find VCR-type devices and camcorders that use hard disks instead of tape. These billions of hard disks do one thing well — they store changing digital information in a relatively permanent form. They give computers the ability to remember things when the power goes out.

In this article, we’ll take apart a hard disk so that you can see what’s inside, and also discuss how they organize the gigabytes of information they hold in files!

Hard Disk Basics

Hard disks were invented in the 1950s. They started as large disks up to 20 inches in diameter holding just a few megabytes. They were originally called “fixed disks” or “Winchesters” (a code name used for a popular IBM product). They later became known as “hard disks” to distinguish them from “floppy disks.” Hard disks have a hard platter that holds the magnetic medium, as opposed to the flexible plastic film found in tapes and floppies.

At the simplest level, a hard disk is not that different from a cassette tape. Both hard disks and cassette tapes use the same magnetic recording techniques described in How Tape Recorders Work. Hard disks and cassette tapes also share the major benefits of magnetic storage — the magnetic medium can be easily erased and rewritten, and it will “remember” the magnetic flux patterns stored onto the medium for many years.

Cassette Tape vs. Hard Disk

Let’s look at the big differences between cassette tapes and hard disks:

* The magnetic recording material on a cassette tape is coated onto a thin plastic strip. In a hard disk, the magnetic recording material is layered onto a high-precision aluminum or glass disk. The hard-disk platter is then polished to mirror-type smoothness.

* With a tape, you have to fast-forward or reverse to get to any particular point on the tape. This can take several minutes with a long tape. On a hard disk, you can move to any point on the surface of the disk almost instantly.

* In a cassette-tape deck, the read/write head touches the tape directly. In a hard disk, the read/write head “flies” over the disk, never actually touching it.

* The tape in a cassette-tape deck moves over the head at about 2 inches (about 5.08 cm) per second. A hard-disk platter can spin underneath its head at speeds up to 3,000 inches per second (about 170 mph or 272 kph)!

* The information on a hard disk is stored in extremely small magnetic domains compared to a cassette tape’s. The size of these domains is made possible by the precision of the platter and the speed of the medium.

­ Because of these differences, a modern hard disk is able to store an amazing amount of information in a small space. A hard disk can also access any of its information in a fraction of a second.

Capacity and Performance

A typical desktop machine will have a hard disk with a capacity of between 10 and 40 gigabytes. Data is stored onto the disk in the form of files. A file is simply a named collection of bytes. The bytes might be the ASCII codes for the characters of a text file, or they could be the instructions of a software application for the computer to execute, or they could be the records of a data base, or they could be the pixel colors for a GIF image. No matter what it contains, however, a file is simply a string of bytes. When a program running on the computer requests a file, the hard disk retrieves its bytes and sends them to the CPU one at a time.

There are two ways to measure the performance of a hard disk:

* Data rate – The data rate is the number of bytes per second that the drive can deliver to the CPU. Rates between 5 and 40 megabytes per second are common.

* Seek time – The seek time is the amount of time between when the CPU requests a file and when the first byte of the file is sent to the CPU. Times between 10 and 20 milliseconds are common.

The other important parameter is the capacity of the drive, which is the number of bytes it can hold.

Inside: Electronics Board

The best way to understand how a hard disk works is to take a look inside. (Note that OPENING A HARD DISK RUINS IT, so this is not something to try at home unless you have a defunct drive.)

A typical hard disk drive is a sealed aluminum box with controller electronics attached to one side. The electronics control the read/write mechanism and the motor that spins the platters. The electronics also assemble the magnetic domains on the drive into bytes (reading) and turn bytes into magnetic domains (writing). The electronics are all contained on a small board that detaches from the rest of the drive:

Inside: Beneath the Board

Underneath the board are the connections for the motor that spins the platters, as well as a highly-filtered vent hole that lets internal and external air pressures equalize:

Removing the cover from the drive reveals an extremely simple but very precise interior:

* The platters – These typically spin at 3,600 or 7,200 rpm when the drive is operating. These platters are manufactured to amazing tolerances and are mirror-smooth (as you can see in this interesting self-portrait of the author… no easy way to avoid that!).

* The arm – This holds the read/write heads and is controlled by the mechanism in the upper-left corner. The arm is able to move the heads from the hub to the edge of the drive. The arm and its movement mechanism are extremely light and fast. The arm on a typical hard-disk drive can move from hub to edge and back up to 50 times per second — it is an amazing thing to watch!

Inside: Platters and Heads

In order to increase the amount of information the drive can store, most hard disks have multiple platters.

The mechanism that moves the arms on a hard disk has to be incredibly fast and precise. It can be constructed using a high-speed linear motor.

Many drives use a “voice coil” approach — the same technique used to move the cone of a speaker on your stereo is used to move the arm.

Storing the Data

Data is stored on the surface of a platter in sectors and tracks. Tracks are concentric circles, and sectors are pie-shaped wedges on a track, like this:

A typical track is shown in yellow; a typical sector is shown in blue. A sector contains a fixed number of bytes — for example, 256 or 512. Either at the drive or the operating system level, sectors are often grouped together into clusters.

The process of low-level formatting a drive establishes the tracks and sectors on the platter. The starting and ending points of each sector are written onto the platter. This process prepares the drive to hold blocks of bytes. High-level formatting then writes the file-storage structures, like the file-allocation table, into the sectors. This process prepares the drive to hold files.

source: http://compreviews.about.com/gi/o.htm?zi=1/XJ&zTi=1&sdn=compreviews&cdn=compute&tm=686&f=00&su=p284.9.336.ip_p504.1.336.ip_&tt=2&bt=1&bts=1&zu=http%3A//computer.howstuffworks.com/hard-disk.htm

A hard drive enclosure is used to house a hard disk externally, adding storage and flexibility to any system. The enclosure connects to the computer through a universal serial bus (USB) or Firewire port, making it a plug-and-play device. This means it can be turned off and on while the system is up and running. A hard drive enclosure can be used for many purposes and provides portability between desktop and laptop, or home and office.

Security: One of the main advantages to using an external hard drive enclosure is security. Many people are concerned about online threats including viruses, Trojan horses, spyware, hacking, poorly written software and malicious scripts. Some threats can expose data to outside sources, while others corrupt it.

Installing financial data or sensitive programs on an external hard drive is one way to help ensure they stay safe. The hard drive enclosure can be left off when the user isn’t accessing the programs or data, and when online. If several family members share the computer, an external drive is one way to keep key information or software private. Simply remove the hard drive enclosure and lock it in a drawer or safe when not in use.

Back Up: An external hard drive is perfect for storing system back ups or “ghost” images of the main hard disk. If the main drives fails, the ghost image on the external drive can re-create the main disk in mere minutes. Alternately, popular software like Acronis True Image will make a bootable carbon copy of the main disk on the external disk. In this case, the external disk can be removed from the enclosure and installed into the system for an instant fix. It is also possible to boot directly from the hard drive enclosure by using settings in the motherboard’s Basic Input/Output System (BIOS) menu.

Archiving and Libraries: People today are rapidly amassing memory-intensive libraries of music, movie, and graphic files. Storage of these libraries using an external hard drive enclosure frees up on-board system resources for ripping, burning and downloading, while protecting libraries from online threats. Moving these libraries to an external drive also greatly reduces maintenance time for system tasks like file defragmentation, spyware sweeping and virus-checking.

A hard drive enclosure also allows people to reuse “smaller” hard disks that have been replaced by newer, larger capacity drives. For example, as prices have dropped many people have replaced 30, 40 and 60-gigabyte (GB) drives with 250 GB drives or better. Installed in an external hard drive enclosure, older drives become quite useful for archiving.

Portability: It’s simple to transport huge amounts of data between computers using an external hard drive enclosure. Any system equipped with a USB port or Firewire will be able to instantly read the drive and transfer files quickly and easily. An external drive is the next best thing to a massive memory stick.

Alternate Operating Systems (OSs): True geeks might like to use an external hard disk to load a bootable, alternate OS, such as an upcoming Windows OS or Linux. Having a fully functional secondary operating system allows for experimentation without unduly risking the main system, its setup or configuration. One can also try out critical programs for compatibility issues. Installing the OS on an external drive avoids the hassle of creating a dual boot system as is necessary when loading two operating systems on internal disks. Motherboard BIOS settings allow one to easily boot from the external storage device or the internal hard disk.

In considering which hard drive enclosure to purchase, keep in mind that the enclosure must be made for the type of hard drive it will contain. Older drives are IDE, which stands for Integrated Drive Electronics. Newer drives are Serial-ATA or SATA drives. The relevant difference is in the imbedded connector and controller. Noise is also a consideration. Some enclosures have a built-in power supply and fan. Fan design determines whether the fan will be quiet or noisy. If you plan to leave the hard drive enclosure on most of the time, you may want to consider a quieter model. Vendors like NewEgg.com provide customer reviews that can be a great asset in making the right decision.

An external hard drive enclosure is so handy you might want more than one. Once you use it, you’ll likely wonder how you ever got along without its many benefits.

source: http://www.wisegeek.com/what-is-a-hard-drive-enclosure.htm