Hard disk

Hard disk or Hard Drive (disk drive, HDD, “Winchester”) is a main storage device in most computers, based on the magnetic recording principle.

Looking on hard disk definition, it’s easy to see that in contrast to the “flexible” disk (floppy), in a case of hard disk the information is recorded on the “hard” materials. A single hard disk usually consists of several platters. Almost always, aluminum or glass plates are used. Each platter requires two read/write heads, one for each side.

Also (unlike a floppy disk or USB flash drive) the hard disk itself is usually combined with some other electronic devices, so it’s ready-to-use storage solution for computer users. Because of that hard drives are often used in non-removable computers.


The hard disk has several basic characteristics:

  • Interface. The way of the interaction between 2 devices of different types. Modern hard drives can use ATA (IDE and PATA), SATA, eSATA, SCSI, SAS and other interfaces.
  • Capacity. The amount of data hard drive can store. Modern hard drives can store up to 5 TB.
  • Dimension. There are a lot of possible dimensions of hard drives: “classic” 8 and 5.25 inches, “standart” 3.5 or 2.5 inches and modern 1.8, 1.3, 1 and 0.85 inches.
  • Random access time. The average time the hard drive performs a read/write operations to a random section of the disc. Usual range of this parameter is from 2.5 to 16 ms (for comparison, this parameter for SSD-drives is less than 1 ms).
  • Energy consumption. The less energy consuming drive, the less you have to pay for its operating. Hard disk consumption for Mobile users directly affects the battery life.
  • Transfer Rate. The rate of data transmission. If this number is low, the speed of copying inside the disk and to an external media will be slow.

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