Hard Disk Drives – Types, Sizes and Future Technology

December 21, 2010 at 1:54 pm by artefact_admin

What is a Hard Disk Drive?

A Hard Disk Drive (Commonly referred to as a Hard Drive or HDD) is a device that stores digital data. It includes rigid platters made from aluminum alloy or glass coated with a magnetic material and housed within a metal case. The data is encoded “magnetically” and float on a cushion of air above the platters.

Size / Form Factor / Capacity

Hard Drives come in various shapes and sizes. The Hard Drive Suppliers and Computer Industry refer to them as 1.8”, 2.5” or 3.5” Form Factor Drives. These “form factor descriptions” refer to the approximate physical diameter size of the “platters” that are housed within the drive casing and account for over 95 % of the drives in use today.

Another way to describe hard drives is by the market segment to which they are designed. You will hear the term Desktop or Server / Enterprise ( 3.5” Drives) or Mobile Drives ( 2.5” or 1.8” ) as a common description.

In order to increase the capacity of data that is stored on a platter, in 2005 the technology of storing information in a longitudinal format ( LMR – longitudinal magnetic recorded ) was changed to a PMR or perpendicular magnetic recorded mode. Virtually all NEW drives purchased today are PMR Drives. In order for this method of recording to be accomplished, the disk areal density (known as
Coercivity ) had to increase up to 5,000 Oersted.

Future Drive Technology

Today’s Hard Drives are based on magnetic media technology with “read/write” heads that read the stored data that resides on the internal platters. Due to the “moving” parts on a hard drive, they are all subject to wear and eventual failure. The good news is that most magnetic drives have built-in diagnostics to warn the user of an eventual failure. This gives the user time to back-up the data to help mitigate the loss of any data. Drives based on “flash memory” are also available. These drives do not have moving parts. These “memory” drives are particularly important in applications where the movement of the drive itself may cause a head crash and thus a catastrophic failure. They are typically much smaller in size and therefore ideal for smaller devices that require data storage. The Hard Drive Industry projects only a small percentage ( about 12% ) of the 675 M unit annual volume will be in use in the next five years.


The most commonly used hard drives in today’s computing world are the 3.5”, 2.5” and 1.8” form factor drives based on PMR Technology. They represent over 95% of the drives currently being used in the marketplace.

While there are some 5.25” Form Factor drives with widths up to 5.75” and heights up to 6” still in use, these drives account for only a small portion of the Hard Drives being deployed today. Future drives will be based on flash memory and will only account for a small portion of the 675 million unit HDD market.

Current major Hard Drive Suppliers who account for 95% of world wide HDD Manufacturing are as follows: Seagate (Owns Maxtor, Quantum), Western Digital, Toshiba (Owns Fujitsu), Hitachi (Owns IBM) & Samsung.

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