How the Hard Drive Works

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HDDA Hard disk is a secondary and permanent data storage device that is placed in the system. It is made up of a magnetic material that helps in storing data by following the magnetic recording techniques. A Hard disk stores data from 1 GB to Terabytes depending on the capacity of the hard disk. A Hard disk consists of several circular platters. Each platter has read/write heads on both the sides. The platters are divided into concentric circles called as tracks and each track is divided into smaller units called sectors. The read/write head examines and records data in these sectors. The identically aligned tracks on each side of every platter together make up cylinder.

Types of Hard disk:

Hard disks can be classified into types depending on the speed at which the hard disk transfers data and the reliability of the hard disk in storing data if the hard disk crashes. The different types of hard disk are:

  1. Serial ATA (SATA)
  2. SCSI Hard Disk Drive
  3. External Hard Disk Drives (USB 2.0/Firewall)
  4. Wireless Hard Disk Drive

Serial Advanced Technology Attachment (SATA)

Serial ATA transfers data using 1 bit with the speed of up to 600MB per second but external SATA is capable of 1.5Gbps. SATA hard disk uses a smaller 7 –wire cable to connect to the system. This cable can have a maximum length of meter. The power cable of SATA Hard disk is smaller than the ‘Molex’ connectors used in ATA hard disks. We can only connect one SATA hard disk to a SATA controller on the motherboard. This eliminates the need to set a Hard disk as Master or slave. We can connect more than one hard disk by connecting them to different SATA controllers on the motherboard using separate cables.

Small Computer Systems Interface (SCSI)

SCSI hard disk is used in network server which includes lot of processing. SCSI is a high speed interface that enables you to connect up to 15 devices on a single port. SCSI is used with the Redundant Array of Inexpensive Disk (RAID), where two or more hard disks are combined together to form a single hard disk. RAID allows to access data quickly and prevents loss of data in case of a hard disk crash.

External Hard Disk Drives (USB, Fire wire)

External hard disk can be connected using USB2 and fire wire interfaces. External HDD also supports high-speed data transfer. External Hard Disks that uses this interfaces consumes the required power from the port through which they are connected like USB or Fire wire.

Wireless HDD

Wireless Hard Disk Drives are small and light in weight. They use 802.11g standard for communication. Wireless HDD requires external power supply. It is a Wi-Fi hard disk.

Characteristics of Hard Disk Drive:

Before selecting a HDD several factors are taken into consideration such as capacity, cost, performance, reliability, RPM of the HDD. The different types of HDD are:

  1. Cost & Capacity: At first the HDD capacity was very less and too costly. With the advancement in technology the cost of the HDD gradually decreased and the capacity of the HDD also increased. Now HDD are available from 500 GB to 1 TB.
  2. Performance: Mainly computer use involves loading and saving data frequently. All these operations require access to hard disk. The performance of HDD depends on the way data is stored and retrieved on the HDD.
  3. Reliability: Hard disk is the most commonly used data storage device. Reliability is measured in terms that the user should be able to retrieve and store the data when required.
  4. RPM: Revolutions Per Minute is the count of the revolutions made by the Hard disk per minute. Faster RPM results in quick access time which in turn results in faster read and writes. IDE HDDs are available in 5400 and 7200 rpm and SCSI are available in 10K and 15K rpm.


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 HDD.

  1. System does not start:
  2. The system will not boot if it cannot load the system files from the HDD. This may be caused due to improper jumper or BIOS settings or some problems with the cable connectors.
  1. Check if the power supply is switched ON.
  2. Remove any floppy disk inserted in the Floppy Disk Drive.
  3. Check if the BIOS is set to boot from the HDD.
  4. Check that the cables connecting the hard disk to the motherboard are connected properly.
  5. Set the proper jumper settings if multiple HDDs are present.
  6. Connect the HDD using a different interface cable that you know is working.
  7. Install the HDD on a different system to check if it is working.
  8. Boot the system using the bootable floppy disk or CD and try accessing the hard disk and scan the disk for errors.
  9. Format and reinstall the operating system on the HDD.
  1. HDD contains Bad sectors: There are several ways in which a Hard disk can develop bad sectors:
  1. A hole in the magnetic thin film on the platter when it was coated.
  2. A defect in the substrate which gets worse with the time.
  3. A mechanical failure which causes the head to contact the platter.
  4. Thermal fluctuations which corrupt magnetic data.
  5. Power loss during a write operation.
  6. Viruses and Trojans causing minor logical damage to the HDD.

Fixing Bad sectors:

  1. Bad sectors can be repaired using the Disk Diagnostics Utility. Go to ‘Start’ — ‘Computer’. Right click on the ‘Local Disk C’ and click ‘Properties’. The ‘Properties dialog box appears.
  2. Click the ‘Tools’ tab and click on ‘Check Now’ button. The ‘Check disk’ dialog box appears.
  3. Select the ‘Scan for and attempt recovery of bad sectors’ option.
  4. Click the start button.
  5. It may ask you to reboot the computer to perform the fixing of bad sectors. Restart the computer to do so.

Hard disk drive crashes:

  1. Remove the HDD from the system.
  2. Install HDD in another system as secondary drive.
  3. If HDD is working, try to copy the data into another storage device (HDD) available.
  4. Format the HDD.

Hard disk does not display the correct formatted size:

  1. Scan the system for viruses.
  2. Use scan disk to check the system for errors.
  3. Check the settings from BIOS.
  4. Check the jumper settings to see if any size restrictions are set for the HDD.
  5. Back up the HDD and reformat the drive.