CHAPTER 7 HARD DISK DRIVES

Introduction :
	A hard disk is the primary and permanent data storage device that is placed in the system. It is similar to a human brain where all the past and present events are stored. It is made up of a magnetic material that helps in storing data for the system by following the magnetic recording techniques. A hard disk stores data from 1 GB to 160 GB or even more depending on the capacity of the hard disk. A hard disk consists of several circular platters and each platter has read/write heads on both the sides of it. The platters are divided into concentric rings, called as tracks, and each track is divided into number of sectors. The read/write heads examines and then records the data in these sectors.
7.1 Types of Hard Disks
	The different hard disks specify the speed at which the hard disk transfers data and the reliability of the hard disk in storing the data if the hard disk crashes.
	7.1.1 Advanced Technology Attachment (ATA)
	The ATA transfers data between the hard disk and the system using 16 bits with speeds of upto 100 MB per second. You can connect two hard disks to a single controller on the system. You must set the hard disk to master or slave using the jumpers on the hard disk, so that the system can identify the required hard disk. This hard disk uses a 40-pin connector to connect to the system.
	7.1.2 Serial ATA
	The Serial ATA transfers data between the hard disk and the system using only 1 bit at a time with the speed of upto 600 MB per second. You can connect only one Serial ATA hard disk to a single controller on the system, thus this hard disk does not have settings such as master, slave or cable select. The Serial ATA hard disk uses a 7 wire cable to connect to the system.
	7.1.3 Programmed Input / Output (PIO)
	The PIO mode specifies that the controller for the hard disk is built into the motherboard. Thus, a separate controller card is not required to connect the hard disk to the motherboard. The PIO supports four hard disks - two hard disks on each channel.
	7.1.4 Redundant Array of Inexpensive Disk (RAID)
	RAID combines two or more hard disks in an array resulting in the increase in the speed of data storage and retrieval. All these hard disks are combined and used as a single hard disk. RAID is implemented on different levels, this provides security for the data stored on the hard disk so that if one hard disk fails the data can be retrieved.
	RAID Level 0
	This level enables you to treat a collection of two or more hard disks as a single unit. The data to be saved is spread out on the hard disk collection. This speeds up the process of reading and writing data as multiple disks are used to store data.
	RAID Level 1
	This level uses disk mirroring. One disk stores the data whereas the mirror disk stores a copy of the data. This ensures that if one disk fails the data can be retrieved from the mirrored disk.
	RAID Level 4
	This level stores the data on multiple disks and stores the sum of the data on a parity disk. If one of the disk crashes the parity disk can be used to recover the data.
	RAID Level 5
	This is the frequently used method to RAID hard disks. This level stores the data on multiple disks, the parity information is not stored on a single hard disk but on different hard disks.
	Linear RAID
	Linear RAID combines the multiple hard disks together to form one drive. While storing data it first fills the first hard disk in the series and after the first disk is full it stores data to the next disk in the series.
7.2 Types of Hard Disk Interfaces
	The hard disk interface specifies the method used by the hard disk to send and receive data to the system using a data cable. The type of the interface specifies the data transfer speed between the hard disk and the system. To use a specific interface you must have the required controller installed on the system.
	7.2.1 Enhanced Small Device Interface (ESDI)
	ESDI hard disk interface is a standard interface for personal systems. It connects the hard disk drives and other removable disk drives to the system. The ESDI interface enables the hard disk to communicate with the system at a speed of 10 MB per second.
	7.2.2 Small Computer Systems Interface (SCSI)
	The SCSI interface enables the hard disk to communicate with the system at very fast speeds. This interface is used on network servers that perform a lot of processing. The SCSI supports upto eight devices on a single cable and is used with RAID.
	7.2.3 Integrated Device Electronics (IDE)
	The IDE interface specifies that the hard disk controller is built on the hard disk. This ensures that the data communication between the hard disk and the controller is fast. The IDE interface also provides for a high data transfer rate between the hard disk and the system.
	7.2.4 Enhanced Integrated Device Electronics (EIDE)
	The EIDE interface supports hard disks that have sizes from 504 MB to 8.4 GB. The EIDE interface supports a maximum of four hard disk drives on a system. The EIDE hard disk is a plug and play device. Thus to use this device you must just plug the device to the system and use it, you do not need to install any special drivers to use the hard disk.
7.3 Components of the Hard Disk
	The different components such as the platters, the read / write head and the head actuator form the hard disk. These components are sealed inside the hard disk compartment known as Head Disk Assembly (HDA).
	7.3.1 Platters
	The platters are round disks that are made up of metal or glass. The platters of glass are preferred, as the shape of the glass does not change when the hard disk heats up. The platters in the hard disk are stacked over each other. The size of the platter determines the size of the hard disk.
	7.3.2 Recording Media
	The recording media is made up of a magnetic material such as iron oxide. This recording media layer is spread on the platters. The system stores the data on this layer of the hard disk.
	7.3.3 Read/Write Head
	The Read/Write head is used to read the data stored on the hard disk and also write the data to the hard disk. While reading, the head converts the data from binary to a magnetic pulse. The magnetic pulse charges the magnetic coating on the platter and stores the data on the disk. While reading data from the disk, the head reads the magnetic data stored on the disk and converts them to binary and sends it to the system. Every platter in the hard disk has two read/write heads one on each side of the platter. While the disk is reading or writing data to the disk the head does not touch the disk. However, when the disk stops spinning the head gently rests on the stationary disk.
	7.3.4 Head Actuator Mechanism
	The head actuator is used to move the read/write head from the center of the platter to the edge of the platter, moving from one track to the next. This enable the read/write head to position itself over the required hard disk sector and access the data from all the parts of the disk when the disk is spinning.
	7.3.5 Air Filters
	The Air Filters in the hard disk clean the air that circulates in the hard disk of the particles that scrape off the platter surface. The hard disk has small vents to ensure that the air pressure in the hard disk is the same as the air pressure outside the hard disk. The hard disk has air filter in these vents that filters the dust particles that may get into the hard disk using these vents.
	7.3.6 Hard Disk Temperature Acclimation
	The temperature acclimation specifies the time that the hard disk must not be used after it is transported from a place having a cold climate to a place having a warm climate. The air vents in the hard disk that are used for equalizing the pressure in the hard disk also let in moisture in the hard disk. If you use the disk, the moisture may condense on the platter and it can cause permanent damage to the hard disk. To prevent this damage due to moisture, you must place the hard disk in the working environment but use it only after the time duration specified in Table 7.1. Previous Climate Temp. Acclimation Time (hours) Fahrenheit Celsius +40°F +4° 13 +30°F -1° 15 +20°F -7° 16 +10°F -12° 17 0°F -18° 18 -10°F -23° 20 -20°F -29° 22 -30°F or less -34° or less 27 Table 7.1 - Acclimation Time
	7.3.7 Spindle Motor
	The Spindle Motor is used to spin the hard disk platters. These motors are very precise and reliable, as they have to spin for many continuous hours. The spindle motor must spin without causing a lot of vibrations as the slightest vibration during the operation of read / write can damage the hard disk.
	7.3.8 Logic Board
	The Logic Board contains the circuit for controlling the hard disk. All the connectors from the system connect to the logic board. The logic board stores the data on the hard disk platters. Sometimes the logic board of the hard disk may fail due to surges in the power supply. In such a case you can replace the logic board of the hard disk.
	Best practices
	1. Switch off the power supply before opening up the system. 2. Unplug all the cables of external devices connected to the system. 3. Attempt to replace the logic board if it is damaged only if you have critical data stored on the disk.
	Precautions
	1. Opening up the hard disk may terminate the hard disk warranty.
	Hands on exercise
	To replace the hard disk logic board : 1. Open the system case. 2. Disconnect the cables connected to the hard disk. 3. Remove the hard disk form the system case. 4. Pull out the logic board out carefully. The logic board detaches itself from the hard disk and appears.
	Detached Logic Board
	5. Attach a new logic board on the HDA taking care to align the connecting pins of the logic board with the connectors on the HDA. 6. Install the hard disk back in the system. 7. Close the system.
	7.3.9 Cables and Connectors
	The cables and connectors connect to the back of the hard disk. You can attach the power cable and the data cable to the hard disk. The cable connectors are attached to the logic board of the hard disk and are keyed to ensure that you insert the cables in the correct manner.
	7.3.10 Configuration Items
	The Configuration Items enable you to set the hard disk using jumpers that are located at the back of the hard disk. These jumpers also enable you to set the drive number as in the case of SCSI drives.
	Hard Disk Jumpers
	You can also set the hard disk to master, slave or cable select as per the jumper settings displayed on a label affixed on the top cover of the hard disk. If you have two hard disks installed on the system, you must set the jumper of one hard disk to master and the jumper of the other hard disk to slave. This ensures that the correct hard disk responds to the system calls. The system considers the master first and then the slave while assigning drive letters. The system also boots the primary partition from the hard disk set as master. You can also set the jumper option to cable select, this ensures that the hard disk is set with the status of master or slave depending on the cable connector used to connect the hard disk. For using the cable select option you must set the jumpers of both the hard disks to cable select and also use a special cable to connect the hard disks to the motherboard. The cable select cable is similar to the IDE cable but has a special pin numbered 28 that connects to the hard disk on the master connector and sets the hard disk as master.
	7.3.11 Faceplate
	The faceplate or the Bezel is the front plastic covering of the hard disk. To install a drive that has a faceplate you must remove a plastic panel from the front of the system case. However, the latest hard disks do not have a bezel.
7.4 Working of the Hard Disk
	The hard disk stores the data on the magnetic platter coating. The user executes a command, or the program requests information from the hard disk. The motor in the hard disk drive rotates the platters. The read write head moves over the required track and the read write head reads the data from the hard disk. The hard disk drive sends the data to the microprocessor for processing. The motor stops rotating the platters in the hard disk. The steps followed by the hard disk to write data on the hard disk: The user executes a command, or the program sends data to be written on the hard disk. The motor in the hard disk drive rotates the floppy disk. The read write head moves over the required track to read the track address from the hard disk for storing the data. The write head is energized. The write head converts the binary data into electromagnetic impulses and writes the data on the hard disk. The motor stops rotating the platters in the hard disk.
7.5 Types of File System
	The file system determines the way that the files and folders are stored on the hard disk. The type of the filesystem that you want to format the hard disk with depends on the operating system that you want to install and the features that the file system offers.
	7.5.1 File Allocation Table (FAT)
	The FAT file system stores the pieces of file data known as clusters on the hard disk. These clusters are stored on different locations of the hard disk. The FAT filesystem has a file allocation table that holds the information where the different clusters of a file are saved. It also lets the system know if a sector on the hard disk contains data or is empty.
	FAT16
	FAT16 uses a 16 bit binary number to identify the cluster number that stores the data on the hard disk. FAT16 file system is used on hard disks that have a medium storage capacity. It can be used on hard disks that have the capacity of upto 2 GB. The operating system such as Disk Operating System (DOS), Windows 3.x and 95 makes use of the FAT filesystem.
	FAT32
	FAT32 uses a 32 bit binary number to identify the cluster number that stores the data on the hard disk. FAT32 file system is used on hard disks that have a very large storage capacity. It can be used on hard disks that have the capacity of upto 2 Tetrabytes (TB). The operating system such as Windows 98 / 2000 / ME / XP makes use of the FAT filesystem.
	7.5.2 New Technology File System (NTFS)
	The NTFS file system offers a high level of security for the stored files. The NTFS file system is reliable as it ensures that when you save data to a file, all the updated data from the memory is saved to the file or none of the updated data is saved. This ensures that the file does not get corrupted when it is saved, due to any physical or technical problems such as a power failure. The operating system such as Windows NT / 2000 / 2003 makes use of the NTFS filesystem.
	7.5.3 Extended File System (EXT)
	The EXT file system has a root directory and all the files and folders are stored in this root directory. The EXT3 file system also has a feature called Journaling that keeps a log file with the data that must be stored on the hard disk. This ensures that the data does not get corrupted due to power failures. The operating system such as UNIX and Linux makes use of the EXT filesystem.
7.6 Installing the Hard Disk
	The system can read and write data to the hard disk after it is installed. You must also set the BIOS settings for the system to identify the hard disk.
	Best practices
	1. Check if the system supports the hard disk capacity. 2. Check the type of the hard disk that you can install. 3. Check the instructions and the settings specified on the label affixed on top of the hard disk. 4. The hard disk may be pre-configured as master as per the factory settings. Let this setting be as it is if you are installing only one hard disk on the system.
	Precautions
	1. Switch off the power supply before opening up the system. 2. Unplug all the cables of external devices connected to the system. 3. Wear an anti-static wristband. 4. Do not drop the hard disk. 5. Insert the signal cables carefully into the hard disk taking care not to damage the pins. 6. Ensure that the marking on the signal cable faces the power cable connector on the hard disk.
	Hands on exercise
	To install the hard disk : 1. Configure one hard disk as master and the other as slave if you are installing two hard disks in the system on the same IDE cable. 2. Open the system case. 3. Locate an empty drive bay in the system case. 4. Insert the hard disk into the drive bay and attach screws to hold it in place. 5. Connect one end of the signal cable to the motherboard.
	Inserting Signal Cable on the Motherboard
	6. Connect the other end of the signal cable to the hard disk.
	Inserting Signal Cable on the Hard Disk
	7. Connect the power cable to the hard disk.
	Inserting Power Cable
	8. Connect the second hard disk, if any to the system. 9. Close the system. 10. Restart the system and press Delete to enter the BIOS setup. 11. Browse to the Standard CMOS Setup page and ensure that the Type options are set to Auto. 12. Save and exit the BIOS. 13. Restart the system. 14. Boot into windows. 15. Create partition on the hard disk using the Disk Management Utility or Fdisk. 16. Format the partitions created.
7.7 Partitioning the Hard Disk
	Partitioning is used to divide the hard disk into sections known as drives. Partitioning makes your system start faster and it also enables you to install multiple operating systems on the different partitions such as you can have Windows 98 on the first partition and Windows XP on the second partition. The different partitions on the hard disk are assigned drive letters to enable you to access the drive. You can have upto four partitions on a single hard disk. You can create partitions using the Fdisk utility. The Fdisk utility enables you to specify the size in MB that you want the size of the drive to be. You can also enter a percentage value that specifies the size of the partition on the hard disk. For example, suppose you have a hard disk of the capacity 10 GB and you specify the partition size as 25%, then Fdisk will create a partition of the size 2.5 GB.
	7.7.1 Primary Partition
	A hard disk can have upto four primary partitions on the system. However, you can only mark one partition as an active partition. This active partition contains the Master Boot Record for starting the system. Your system must have one Primary partition.
	7.7.2 Extended Partition
	A hard disk drive can have only one extended partition. The extended partition can be further divided into logical drives. The logical drives are assigned drive letters to identify the drive.
	Best practices
	1. You must decide the number of operating systems that you will install on the system before you partition it. 2. You must decide the size of the partitions based on the data that you will store on the partition. 3. Copy and paste the file Fdisk.exe from the C:\Windows\Command folder located on a system having Windows 95 / 98 to a bootable floppy disk. A bootable floppy disk has system file that enables you to start the system using the floppy disk. 4. Restart the system after creating all the partitions and drives using Fdisk.
	Hands on exercise
	To create a primary partition using Fdisk: 1. Restart the system and insert the bootable floppy in the floppy disk drive. 2. Type Fdisk at the command prompt and press enter. The system displays the information.
	Information Screen
	3. Type Y and press enter. The Fdisk Options Page appears.
	Fdisk Options Page
	4. Select 1 and press Enter. The Create DOS Partition or Logical DOS Drive screen is displayed.
	Create DOS Partition or Logical DOS Drive Screen
	5. Type 1 and press Enter. The Create Primary DOS Partition screen is displayed
	Create Primary DOS Partition Screen
	To create a primary partition using all the available space on the hard disk, type Y and press Enter. 6. Type N and press Enter. The screen set the size of the partition is displayed
	Setting Partition Size
	7. Type the required partition size in MB such as 600 to create a primary partition of 600MB and press Enter. The screen displaying the information of the partition created is displayed
	Displaying Partition Information
	8. Press Esc. The Fdisk options page is displayed. 9. Press Esc to exit Fdisk. To create an extended partition: 1. Run the Fdisk utility. The Fdisk options page is displayed. 2. Type 1 and press Enter. The Create DOS Partition or Logical Disk Drive screen is displayed. 3. Type 2 and press enter. The Create Extended DOS Partition screen is displayed.
	Create Extended DOS Partition Screen
	4. Type the size in MB that you want to set the size of the extended partition and press Enter. The extended partition is created and displayed.
	Displaying Extended Partition the Created
	5. Press Esc to return to the Fdisk options page. 6. Press Esc to exit Fdisk. To create logical drives on the extended partition: 1. Run the Fdisk utility. The Fdisk options page is displayed. 2. Type 1 and press Enter. The Create DOS Partition or Logical DOS Drive screen is displayed. 3. Type 3 and press Enter. The screen to create logical drives is displayed
	Creating Logical Drives Screen
	4. Type the size in MB that you want to create the logical drive such as 260 and press Enter. The screen shows the logical drive created.
	Displaying Logical Drive Created
	5. Similarly, you can create logical drive using the disk space on the extended partition. 6. Press Esc after all the logical drives are created. The Create DOS Partition or Logical Drive screen is displayed. 7. Press Esc to return to the Fdisk Options page. 8. Press Esc to exit Fdisk. To set the active partition: 1. Run the Fdisk utility. The Fdisk options page is displayed. 2. Type 2 and press Enter to set a partition as an active partition. The screen displaying the different partitions created is displayed.
	Displaying Partitions
	3. Type 1 and press Enter to set the primary partition specified at 1 as the active partition. The primary partition is set to active and the screen is displayed
	Setting Active Partition
	4. Press Esc to return to the Fdisk options screen. 5. Press Esc to exit Fdisk.
7.8 Formatting the Hard Disk
	Formatting the hard disk creates the sectors, tracks and places the file system on the hard disk. This prepares the hard disk so that the system can store files on the hard disk. Formatting a hard disk erases all the contents of the drive. Therefore, you must back up the files on the system before formatting a hard disk. You must also format a hard disk after you install a new hard disk on the system or to erase all the contents on the disk, especially if the disk is infected with a virus that cannot be cleaned by the anti-virus software.
	7.8.1 Low Level Formatting
	The Low Level formatting is also called physical formatting. During low level formatting the system creates the tracks and the sectors on the hard disk. The hard disk is formatted using low level formatting at the factory.
	7.8.2 High Level Formatting
	The High Level formatting is also called logical formatting. This creates the necessary file systems on the hard disk for storing the files and folders on the hard disk. You can use the software format.com to perform a high level formatting. You can copy this file from the Windows\Command folder and paste it on a bootable floppy that enables you to start the system when it does not boot. The system also performs a high level formatting during the process of installing the operating system.
	Precautions
	1. Formatting the hard disk will delete all the data on the disk.
	Hands on exercise
	To format the drive of a new hard disk : 1. Insert the bootable floppy disk that has the file format.com in the floppy disk drive. 2. Start the system. The system boots using the files on the floppy disk and displays the command prompt. 3. Type the format command followed by the drive letter and press Enter. For example to format the C drive type the command at the command prompt
	Typing the Format Command
	4. Press Y and press Enter when the system displays a warning and requests for a confirmation to format the drive. 5. After the format is complete the system will request for a label name for the drive. Type a name such as jack and press Enter. To format a drive when an operating system is already present on the hard disk: 1. Open Windows Explorer. 2. Select the drive that you want to format. 3. Right-click and select Format from the pop up box. The Format dialog box is displayed
	Format Dialog Box
	4. Click Start. The formatting starts and a message box is displayed when the format is complete.
7.9 Troubleshooting
	You must troubleshoot the hard disk when the system does not start, the system displays errors while booting or the hard disk does not display the correct storage capacity. You must also check that there is no power leakage from the power supply case as this can damage the hard disk.
	7.9.1 System does not Start
	The system will not boot if it cannot load the system files from the hard disk. This may be caused due to improper jumper or BIOS settings or some problems with the cable connecting the hard disk to the motherboard. 1. Check if the power supply is switched on. 2. Remove any floppy disk inserted in the floppy disk drive. 3. Check that the BIOS is set to boot from hard disk. 4. Check that the cables connecting the hard disk to the motherboard is connected properly. 5. Remove the signal cable from the hard disk and connect it right side up, if the cable is not keyed. 6. Check that one hard disk is connected as the master and one as the slave if two hard disks are connected to the system. 7. Connect the hard disk using a different signal cable that you know is working. 8. Install the hard disk on a different system to check if it is working. 9. Boot the system using a bootable floppy disk or CD and try accessing the hard disk and scan the disk for errors. 10. Format and reinstall the operating system on the hard disk.
	7.9.2 The Hard Disk does not Display the Correct Formatted Size
	The hard disk does not display the correct size that it is formatted with. It displays a size that is less than or more that required size. 1. Scan the system for viruses. 2. Back up the hard disk and reformat the drive. 3. Use scan disk to check the system for errors. 4. Check the jumper settings to see if any size restrictions are set for the hard disk.