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A ‘Hard Disk Drive’ (HDD) is in fact, an integral part of all kinds of data processing in the computer. They are constantly read from and written on, storing and retrieving information on the fly. The HDD is magnetic media that facilitates storing of data inside the computer for retrieval or editing at a later date. They are powered by a set of wires running from the ‘Switching Mode Power Supply’ (SMPS) that connected into the power cable slot on the HDD. The basic read and write operations are then carried out through electromagnetism, which drive the ‘U’ shaped read and write heads inside the body of the HDD. Formally called ‘Winchester Disk Drives’, fixed HDD based on a printed circuit board is made up of platters mostly aluminium or glass, lined up one above the other and pivoted around a spindle, which spins these platters when data is read and written onto them. The HDD is connected to the motherboard with conductor ribbon cable that carries signals between the bus adapter circuits and the controller. Depending upon the usage, amount and processing speed of data, HDD comes in more than one format and form. The HDD also includes the drive controller, which is necessary to ensure that data is read from and written onto by the movement of precision mechanical parts inside the body of the HDD. The ‘FDISK’ command under ‘DOS’ prepares the boot sector of the HDD in such a way that different operating systems with different file systems can co-exist on a single physical HDD. Each and every HDD needs to be formatted before using it to store data. On ‘DOS’ based systems, the ‘FORMAT’ command achieves this purpose. One of the most critical components in a computer, the HDD has evolved a lot in terms of speed and storage capacity. A HDD is actually a sealed aluminium box with controller electronics attached to one side, contained on a small board that detaches from the rest of the drive. Under the board are connections for the motor that spins the platters, also a highly filtered vent that lets internal and external air pressures equalize. Each HDD comes with the same basic features but what varies is how the parts function. The platters, spindle motor, heads and head actuator are inside the drive, sealed from outside. This layout is called the ‘Head Disk Assembly’ (HAD). The externals are made up of the logic board, bezel, and mounting equipment. The platters are the disks inside the drive, which can vary in size. Often, the size of the drive is based on the size of the platters. Most drives have two or more platters. The larger the capacity, the more platter, usually made up of an aluminium alloy, the newer platters however use a new technology of glass/ceramic platters. Many popular manufacturers already use it, as glass platters can be made much thinner than aluminium and can resist the heat better. Each platter is coated with a film of some magnetically sensitive substance. A mixture of compound syrup is poured on the platter, which evenly distributes the film over it. The other main media consists of a thin film of a cobalt alloy, which is placed on the platter through electroplating, much like chrome. There is an arm that holds the read/write heads, which is controlled by the mechanism in the upper-left corner. This 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. On a typical HDD, the arm can move from hub to edge and back up to 50 times per second. The head actuator is the device that all heads are attached to. There are two ways as to how the heads move around the platters. The actuator comes in type: stepper motor actuators and voice coil actuators. The stepper motor design is believed to be inferior as it suffers from slow access rate and is also very sensitive to temperature. Sensitive to physical orientation, it can’t automatically park the heads in a safe zone. In heads in the voice coil actuator, found in all modern drives, this ensures that proper tracks are read. This is unlike the stepper design. The guidance system of the heads is called servo and it positions the head over the correct cylinder. This is done through grey code, which is a special binary number system in which any two adjacent binary numbers provide information to the servo as to their positions on the drive. The heads usually have a coil of copper wiring and when current is passed through the wiring, the surface under it is magnetized, creating one bit of data. The direction of the current in the wiring determines the polarity of magnetization, creating either a 0 or a 1. To read the data again, the electronics of the drive sense the polarity changes and determine a 0 or a 1. After it reads this data, it first takes apart the data from the clock signals. The disk controller to check if this is what the computer wants verifies the data. If it is, it keeps going. If not, it ignores that bit of data. Bit after bit, the useful data is converted from serial to parallel from so that it moves towards the computer’s bus. A data separator integrated onto the drive does this, on IDE and SCSI drives. Other designs convert the data in disk controller. Data on a hard drive is stored in tracks. Tracks are concentric circles; each track is divided into sectors. The two main ways to record the data on the drives are ‘Modified Frequency Modulation’ (MFM) and ‘Run Length Limited’ (RLL). MRM encoding takes 17 sectors per track. RLL encoding uses 16 sectors per track hence packaging more information in less disk space. When the HDD is powered down, the springs attached to the heads pull them into the platter. This is called a landing. Every drive is designed to handle thousands of takeoffs and landings. When powered on, the drive automatically embarks itself and the parking springs are taken over by a magnetic force. The spindle motors are set to spin the platters at a set rate, ranging from 3600 RPM to 7200 RPM. The motor is attached to a feedback loop, which ensures it spins at exactly the same speed that it is supposed to. The speed cannot be adjusted during operation. The location of spindle motors can vary from being at the bottom of the drive, below the HAD, or built into the hub of rotations of the platters, thereby taking up no vertical space to allow more platters. Attached to the spindle motor is a ground strap, which helps the drive get rid of the static charges, created by the rotation of platters through the air. Underneath the drive is the logic board, the board of chips. It controls the spindle and head actuator and translates data to a usable form by the controller and the rest of the system. HDD needs to be handled with care; it doesn’t handle shocks very well, and is quite expensive. If it is dropped, it might be more dead than alive. IDE has become the default standard in HDD but the choice of HDD must be based on the environment of usage and the performance level desired. The interfaces between the disk and the computer that is IDE, SCSI, EIDE, etc. share a few attributes. All of them have an interface adapter card and the ability to interpret data. They can send data to the disk and retrieve it when needed. The actual data storage differs between the interfaces. ‘Integrated Drive Electronics’ (IDE) drives are the default drive on most modern computers. IDE systems put most of the electronics on the drive itself. The encoding and decoding and the control signals are done on the circuit board under the drive. The adapter card relays the signals from the drive to the computer. IDE and ‘Integrated Drive Electronics’ (EIDE) interfaces come as standard, ATA, Fast ATA-2, ATA-3 Ultra DMA, ATA-66. IDE and EIDE style hard drives connect to the computer usually via a built-in connector on the motherboard. As many as 2 drives can be connect to a single 2 headed cable. A computer can have a total of 2 IDE/EIDE hard drive cables connected. The first cable is the motherboard connector and the hard drives attached to it are referred to as primary. The second set is called the secondary. Each of the cables has own designation of master and slave. SCSI is pronounced as “SKUZZY”. The ‘Small Computer System Interface’ (SCSI) drives are independent and their bus is far different from the others. They do not rely on the BIOS to be able to communicate to the computer. When the computer boots, it checks for additional hardware ROMs. As it does this, it finds the SCSI adapter card, if available. It gets no details as to what is attached to the adapter. As many 7 SCSI devices can be connected to the adapter. The adapter watches the flow of data across the SCSI bus. Each device gets its own SCSI address and can talk with the other SCSI devices across the bus. The SCSI interface speeds up the computer. There are no set standards for SCSI; there is the original SCSI and the newer SCSI 2. Proprietary SCSI standards of many companies may not be able to get with a SCSI device of a different brand. EIDE means Enhanced IDE, which does not carry come of the limitations of the original IDE interface. Maximum four devices can be put on one controller. EIDE even allows non-disk devices to be used, such as CD-ROMs. The original IDE allowed only hard drives. EIDE allows the use of much higher capacity drives. It allows a transfer rate of around 11.1 MB per second, which is much faster than IDE. The capacity depends on the environment in which the drive will be used. Desktop or workstation systems, most of the time, these need 20 Gigabytes to 60 Gigabytes of disc drive storage. Servers, audio-video, and CAD systems are believed to require 8 Gigabytes to 73 Gigabytes of disc drive storage. The capacity estimations above can soar depending on the number, size of program applications installed and the environment related to the system. Several factors may be considered when the reported capacity of a disc drive is seen. There are two different number systems to express units of storage capacity; binary, which says that a kilobyte is equal to 1024 bytes, and decimal, which confirms that a kilobyte is equal to 1000 bytes. The storage industry standard adheres to the decimal method. The performance level necessary depends more on how the system is being used. The average home or small business desktop user is not put to high-level performance. Hence it is believed that ATA, Performance ATA or SCSI be used for this category. Mid-range servers and workstations designed for business environments with light to medium workloads have approximately 10 to 50 people accessing the server at a time or workstations on an arbitrary basis during usual business hours. Performance SCSI is considered best for this usage category. High performance servers and workstations designed for mission critical, heavy-use file servers could probably stick to the high-end SCSI. Where more than 50 people are at a time accessing workstations and are logged on to servers on 24 hours a day basis, nothing else could really be better. There are some steps to determine the drive interface. Refer to the system documentation on the current drive. Check system properties. To do this through the device manager in Widows 95/98; select start; settings; control panel. Open the system icon. Click device manager tab. Spread out disk drives heading. Check the phrase “GENERIC IDE DISK TYPE”. If it is found then the machine supports IDE drives. If the SCSI controllers heading is found then the machine may support SCSI hard disk drives. Check the drive cable and connector. If hard disk drive or CD-ROM drive is currently installed then the interface can be determined by checking the drive cable or connector. If the drive connector matches this 40 pins connector with 50 mm wide cable then an ATA interface drive is there. If the drive connector matches narrow SCSI interface of 50 pins connector with 63 mm wide cable or wide SCSI Interface of 68 pins connector with 43 mm wide cable then a SCSI drive is there. HDD is the heart beat of the system and its installation can be an interesting challenge. Buying a new HDD is probably the simplest decision one makes when in need of some big fat space for those gigs of games and MP3’s. Just make a phone call to the vendor and ask for the biggest, leanest, fastest and cheapest HDD. The real trouble starts when it comes to installing a HDD. Unlike PCI cards which can be simply inserted into their respective slots, one first needs to make appropriate space for the HDD, then connect the IDE and power cable, make proper jumper settings and finally ascertain that the HDD is secured firmly in it’s position and completely immobile. HDD is available in two types of interfaces like ‘Integrated Device Electronics’ (IDE) or ‘Enhanced Integrated Device Electronics’ (EIDE) and ‘Small Computer System Interface’ (SCSI). IDE is the defector standard for all desktop computers. Servers and laptops however prefer SCSI interface, as it is more rugged compared to IDE. Each of the myriad SCSI manufacturers has unique techniques of installing. Ground against any static electricity. Touch the metal chassis to discharge any electric current from the human body and then turn of the power supply and remove the plug. Tie any anti-static wrist-strap before opening the computer to protect against a possible electric sock. Most hard disk drives spin either at 5400 RPM or 7200 RPM, which is approximately the speed at which the tires of an airplane move when it takes off, making them extremely fragile. HDD has a plastic protection at the edges, but an occasional drop can render the drive useless. So be extremely careful in handling the HDD. The dorsal side of the HDD contains some circuitry. Regardless of whether it is properly shielded or not, HDD must be kept on top of a non-conducting material like magazine or newspaper to prevent any short circuit. A HDD is said to be “Master” drive if it has been directly connected to the computer. When another HDD is connected to the drive already connected directly to the computer, then the former HDD is said to be “Slave” while the other is “Master” drive. While installing, make sure the jumper settings are correct i.e. in master or slave mode. If not, the CMOS may display messages such as “Boot failed” or worse, fail to detect the HDD. On top of every HDD, there is a small rectangular box, which gives a pictorial representation explaining the jumper settings to be made when connecting the HDD in master or slave mode. To remove the jumper, make use of a small pointed tool, usually a pin, insert it in the middle of the jumper and slowly remove it. Again be careful as excess amount of force breaks the jumper pins. IDE connector is a male connector at the back of the HDD. An IDE data cable is connected to it. Inserting the data cable into the connector can be quite tricky, as both the top and bottom side look quite familiar. So ensure doubly before inserting the cable. While removing the IDE cable, adopt a zigzag manner. Pulling it the way we plug-out the iron socket can do irreparable damage to the IDE cable. The same applies while connecting or removing the power chord. After making proper connections and jumper settings, secure the HDD in the appropriate sized bay 3½” or 5¼”. Normally HDD comes in 3½” sized bays. It may be possible that all 3½” bays are pre-occupied. Under such circumstances, make sure of a mounting bracket and proper screws for the 5¼” bay. It is mandatory to secure the HDD firmly before one starts using. A loose fit makes the drive shaky and even a minor jerk, when the drive is in operation will cause irreparable damage. Once these prerequisite steps are completed, start the computer. The HDD settings now need to be configured in the CMOS. In most cases, the “Auto-detect” option will successfully detect the HDD. Under rare circumstances, one may need to specify cylinders, sectors, heads, write ProComm, landing zone, and the size manually. These details are normally found on top of the HDD. If not, check the accompanying user’s manual. Nowadays, it is common to find 20 GB and 40 GB sized HDD. For those who buy these drives with the sole purpose of replacing their 8 GB or less HDD, ensure that the accompanying CMOS supports the capacity of the HDD to be installed. Some CMOS chips can be made to provide support to the HDD by downloading an upgrade from the manufacturer’s website. If that doesn’t do the trick, buy a new CMOS chip. It is a gruelling task to install it. Installing a HDD can at times be tedious. Be extremely careful while handling the drive as its fragility makes it very susceptible to damage. There are specific instances when the HDD will give problems. When the HDD goes on a troubling spree, it really becomes tough to manage the mess. Sometimes the ultimate options available is formatting the disk and losing all the data. The CMOS knows about the HDD, but it still won’t boot, and there are errors. Formatting and partitioning the HDD is required. This should be done before it is used. Positively in most of the cases, to mount it upside down is not a good idea though. To add info about a new HDD to the CMOS, usually the F1 or F2 key can be hit during boot up. Some systems allow doing it by hitting Ctrl-Alt-Esc, Alt-F2, or Ctrl-S. If not this then the manual may work. If the drive works as a slave, but not as a master, and as a master not as a slave then the settings differ for every drive and this problem is related to that particular setting. Check the master and slave jumper on the back of the drive and consult the manual for correct settings. If the HDD works fine in one system and then stops working when it is moved or motherboard is upgraded, check all configuration and connections. It could also be an incompatibility between the BIOS and the HDD. The translation mode affects how the system reads data off the drive sectors. If boot from the drive doesn’t work but booting off a system disk does then this is because formatting and partitioning has not yet happened to the drive. Maybe the damaged boot sectors or possibly a virus. Scan the drive with a virus scanner. Check if the primary partition is active so that it is bootable. If HDD gets hot and hotter then HDD normally generates a lot of heat. However don’t let them get too hot touch, the newer drives especially. A well-ventilated case should do the needful. If the HDD just won’t work then check the power connection. The spare power connectors if any, in the system, might have gone badly. Check all connections and jumpers. If the HDD won’t boot or says “C: drive failure, insert boot disk” then check error message on the screen and act accordingly. Boot the system with a floppy disk or use the system disk. If the HDD can be read then the drive and controller are fine. May be a boot sector is damaged. Re-copy “COMMAND.COM”, “AUTOEXEC.BAT”, and “CONFIG.SYS”, than retest, if error persists, the drive may be dead or dying. If the machine doesn’t allow a partition over 2 GB in size and if the machine has a FAT 16 file system then this limitation will come built-in to the operating system. Windows 95 OSR 2 and Windows 98 are however capable of using the FAT 32 system, which will get rid of this problem. Else, divide the drive into partitions where each is less than 2 GB. If the HDD seems to have failed then the HDD is not bootable or cannot be detected by the computer. If it is not auto-detectable by the BIOS, it might be a drive failure. If running a scan disk utility finds occasional errors then some files get corrupt during various operations. However, if there are excessive errors the problem is aggravated. Check for viruses. Ensure the shut down procedure is followed properly. If the system fails to recognize the large size of the disk then the BIOS is an old version and cannot recognize a drive larger than this. An up-gradation in the BIOS is required. A driver called dynamic disk can be installed that serves as a medium between a large disk drive and the old BIOS. If a new HDD changes all the drive letters then letters are first assigned to the primary partition, than the logical drive partitions and later to the other drives. They will change if a primary partition is created on the new drive. Create only logical partitions on the second drive. The disk should be formatted and partitioned before using. A necessary step to HDD preparation, formatting, cannot be ignored, and most installation cases require a high level format. When getting a new drive ready, it is required to use the “FORMAT C: /S” command. This high-level command formats the volume drive C; copies hidden operating system files to the volume and asks for a label. The bad sectors are marked as unreadable. This command also overwrites the boot sector and creates the FAT. The root directory is written and system files are copied. The second style of formatting is the low-level format and this is already done on the drive. The low-level format on the HDD is needed to erase all traces of data on the disk or remove corrupted operating systems and viruses or map the drive to relocate all bad sectors to other sectors thus replacing bad sectors with good ones that is called defect mapping. Manufacturers recommend not using low-level format on the HDD.