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Hard Drive Interview Questions

Q   |   QA

  • Hard drives are usually devices that can be used for storing data and to retrieve it. They are composed of one or more than one rigid disc that rapidly rotates.
  • The discs are magnetically coated and use magnetic heads to read and write data on them.
  • They are also known as the secondary storage devices used to store large amounts of data.
  • They can be classified into the following types : Non-Volatile, Digital, Magnetic or data storage devices.
  • Hard drives have been dominant since the use of personal computers as they allow large amounts of data to be stored at low costs and high reliability. 

  • Hard disks in them contain various components such as Platter, Spindle, Actuator, power connector, Jumper block, IDE connector etc.
  • In the inside of a hard disk there is the spindle which is used to hold circular magnetic disks also known as platters. They are usually made up of a non magnetic material, ( aluminum alloy).
  • These platters are spun at speeds in excess of 4000 RPM, nowadays 7200 RPM based hard disks are common enough.
  • The read and write heads work on these spinning platters to read and write data. They are controlled by an actuator arm that prevents any error. 

  • In a hard disk information / data is written on the rotating platters by the read and write heads.
  • The heads are not in actual contact with the disk they are actually slightly above the magnetic surface of the platter.
  • The heads detects the magnetization of the platter right below them. The actuator arm aids the heads in covering the platter area.
  • The surface is divided into micro sized areas known as magnetic domains. Every magnetic domain has a magnetic dipole which has their own field.
  • The write heads read/write by magnetizing the area. It generates a strong magnetic field for this purpose.

There are various ways in which modern hard disks handle errors.

  • Most hard disks use ECC`s error correcting codes mostly the Reed-Solomon error correction techniques.
  • The error checking codes usually employ the use of complex algorithms mathematically derived to store extra bits. These bits are used to correct various errors.
  • Nowadays most of the drives support LDPC or the low density parity check codes.
  • The LDPC allows performance to reach the Shannon limit and also result in the highest storage capacity drives.

  • Generally the controller determines how the hard disk is presented to the host system.
  • In general the modern SATA and SAS present themselves as contiguous set of logical blocks, They are usually 512 bytes long.
  • Formatting can be classified into two types high level and low level formatting.
  • The process through which the logical blocks are initialized on the physical platters is known as low level formatting. This is generally performed during production itself.
  • Once the low level formatting is performed then high level formatting is performed to write the file system structure into the particular logical blocks.

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