Definition

HDD form factor (hard disk drive form factor)

Contributor(s): Carol Sliwa

HDD form factor (hard disk drive form factor) is the size or geometry of a data storage device equipped with one or more magnetic-coated spinning platters and one or more moving actuator arms with magnetic heads to read and write information.

The HDD form factor determines the storage device’s physical compatibility with the drive bays in a storage array or enclosure, server, portable computer or other computing system or consumer electronics product. Industry standards dictate options for the length, width and height of HDDs as well as the position and orientation of the host interface connector.

The most common form factors for HDDs in enterprise systems are 2.5-inch, also known as small form factor (SFF), and 3.5-inch, also known as large form factor (LFF). The 2.5-inch and 3.5-inch measurements represent the approximate diameter of the platter within the drive enclosures. Enterprise-class HDD enclosures, or boxes, typically have a standard length and width. They can vary in height, up to 15 mm for SFF and up to 26.1 mm for LFF.

The 3.5-inch desktop HDD form factor offers a range of height options, from 19.9 mm to 26.1 mm. The mobile 2.5-inch HDD form factor ships in heights ranging from 5 mm to 15 mm. Two of the most popular mobile form factors are single-platter 7 mm and dual-platter 9.5 mm.

Many solid-state drives (SSDs) are designed for the HDD form factor. SSDs that fit into the same slots as HDDs generally use the serial ATA (SATA) or serial-attached SCSI (SAS) interface to transfer data to and from the host computing system.

This was last updated in August 2015

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What are the most popular form factors for enterprise HDDs?
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I'm taking a stab in the dark here because it's been a while since I've been onsite at a larger enterprise office. I think it's still larger desktop drives that can be physically secured to desks and bundled along with workstations. As businesses get more streamlined and smaller, I've seen a lot of portable external drives - mostly because personnel uses laptops a lot more when in this scenario. For my business, I use portable HDD and am even contemplating setting up all my employees on flash memory drives...SSDs. Still waiting for price to move downward.
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I've found that storage arrays are the only spot where form factor is now an issue. Towers, desktops and more are fading away as folks leverage laptops and netbooks to perform their jobs. In fact, cloud storage might be fast making the discussion over form factor a thing of the past for business - but not for Amazon and those companies that serve up this storage.
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