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How Hard Drives Work


hard drives, hard disks, hard discs, disk drives
In order to better understand the data recovery process, it may be helpful to learn a bit about how hard drives physically work.

Hard drives store data magnetically on glass or aluminum disks, or "platters." Every few years, the capacity of hard drives goes up due to new advances in data storage technology; current drives usually store from 40-500GB of data, though drives that store up to 1 terabyte (1,000GB) of data are available and larger hard drives are expected by the end of 2007.

A spindle spins the platters under read/write heads, which are able to magnetically write and read the data which is stored on the magnetic surface of the hard disk platters. While in operation, the heads of the drive never actually come into contact with the hard drive's platters unless the drive suffers a fairly severe physical failure; rather, they float slightly above the platters while reading, writing, and seeking information.

The heads of a hard drive can move back and forth across the surface of the platters at extremely high speeds in order to seek specific sectors of data. They're also extremely precise, and read and write data at blindingly fast speeds. Because the heads of the hard drive are so sensitive, it's important that hard disks aren't subjected to large amounts of physical shock that may cause them to become damaged or misaligned.

The PCB or logic board (the green electronics board on the bottom of the drive) of a hard drive is the electronic board the controls the flow of data between the computer memory and often contains critical information that the drive needs to function properly in the form of
specialized microcode. This information is often specifically programmed to the board of the drive during the drive's construction to meet each individual drive's specifications.

In addition, much more microcode is located within the service area of a hard disk's platters. In fact one side of a platter is specially reserved to store information about the drive. The information contained in the system or service area of the hard drive are as follows:

Relational information about the drive's heads. The drive must be programmed so its heads can work together. slight differences between drives make this information unique to every hard drive. Factory-born defects contained on the drive (often called a P-list). Again, this information is unique to every hard drive. According to data recovery experts, the chances of two 300GB drives having the same factory defect table is roughly one in 500 trillion. Just one lost defect from this table and your data will not be recoverable unless you you contact a data recovery company such as Data Recovery Lab who have the expertise to recover the lost data.

Hard drives, Hard Discs, Hard DisksA list of sectors that have gone bad since you owned the drive (called the G-list). While not as critical, a misappropriated or "bad" sector can cause your data to become temporarily inaccessible. This should be recoverable by any competent data recovery company.

The zone table of the drive also contains critical information tells the CPU about the density of data on the platter as the heads move from the inner part of the platter to the outer edge. Heads map tells the drive in what order it should use a disk head, and also how many heads there are in the drive. SMART log keeps track of operating specs, and flags the BIOS when failure is imminent.

In recent years, hard drive manufacturing companies have researched ways to safely spin platters at extremely high speeds, currently up to 15,000 RPM. These incredibly high speeds help reduce seek time and increase the rate at which data is read by the hard drive and sent to the CPU. The higher speeds are also concurrent with a move to scale down the physical size of hard drive components; this allows for better and more secure data storage.

When a hard drive fails, one or more of the physical components of the drive are usually to blame. By getting the drive to an operational state long enough to copy data off of the hard drive's platters, data recovery technicians are able to maintain a high rate of recovery without risking any sort of damage to the hard drive.

What is data recovery?

Data recovery is the process of salvaging data from damaged, failed, wrecked or inaccessible primary storage media when it cannot be accessed normally. Often the data is being salvaged from storage media formats such as hard disk drive, storage tapes, CDs, DVDs, RAID, and other electronic storage devices. This can be due to physical damage to the storage device or logical damage to the file system that prevents it from being mounted by the host operating system. Data recovery can also be the process of retrieving and securing deleted information from a storage media for forensic and investigation purposes.

Physical damage:

A wide variety of failures can cause physical damage to storage media. CD-ROMs can have their metallic substrate or dye layer scratched off; hard disks can suffer any of several mechanical failures, such as head crashes and failed motors; tapes can simply break. Physical damage always causes at least some data loss, and in many cases the logical structures of the file system are damaged as well. This causes logical damage that must be dealt with before any files can be salvaged from the failed media.

Most physical damage cannot be repaired by end users. For example, opening a hard disk in a normal environment can allow dust to settle on the surface, causing further damage to the platters and complicating the recovery process. Furthermore, end users generally do not have the hardware or technical expertise required to make these repairs; therefore, a data recovery company such as Data Recovery Lab are consulted to salvage the data using specialist tools.

Data recovery specialists often use Class 100 clean room facilities to protect the media while repairs are being made. The extracted raw image can be used to reconstruct usable data after any logical damage has been repaired. Physical recovery procedures include removing a damaged PCB (printed circuit board) and replacing it with a matching PCB from a healthy drive (this often entails the movement of a
microchip from the original board to the replacement), changing the original damaged read/write head assembly with matching parts from a healthy drive, removing the hard disk platters from the original damaged drive and installing them into a healthy drive, and often a combination of all of these procedures. All of the above described procedures are highly technical in nature and should never be attempted by an untrained individual and must only be entrusted to a trained data recovery technician.

Logical damage:

Far more common than physical damage is logical damage to a file system. Logical damage is primarily caused by power outages that prevent file system structures from being completely written to the storage medium, but problems with hardware (especially RAID controllers) and drivers, as well as system crashes and or electro-static discharge (ESD), can have the same effect. The result is that the file system is left in an inconsistent state. This can cause a variety of problems, such as strange behaviour (e.g., infinitely recursing directories, drives reporting negative amounts of free space), system crashes, or an actual loss of data. In these cases, the disk space is identified by the Operating System as "unallocated space". This means that the logical structure or logical format of the drive has been destroyed and consequently data is lost. Data recovery technicians often use disk editors to correct the logical structure of the data and make the drive accessible to the Operating System.

Some types of logical damage can be mistakenly attributed to physical damage. For instance, when a hard drive's read/write head begins to click, most end-users will associate this with internal physical damage. This is not always the case, however. Often, either the firmware on the platters or the controller card will instead need to be rebuilt. Once the firmware on either of these two devices is restored, the drive will be back in shape and the data will be accessible. Data recovery specialists use special tools which operate the hard drive in safe mode enabling them to reconstruct or update the hard disk firmware.

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