form factor is today used by most desktop hard drives. They usually have 10 mounting holes with American 6-32 UNC 2B threads: three on each side and four on the bottom. "2.5-inch" drive: (2.75 in × 3.945 in × 0.374 in = 69.85 mm × 100.2 mm × 9.5 mm)This even smaller, form factor is widely used today in notebook computers and similar small-footprint devices. One commonplace feature for these drives is radically lower power consumption than is found in larger drives. This enables enclosure vendors to power the devices directly from the host device's USB or other external bus, in most cases. "1.8-inch" drive: Found in extremely compact devices, such as certain portable media players and smaller notebooks, these devices are not standardized like their 2.5 inch cousins. A range of other form factors has emerged for mobile devices. While laptop hard drives are today generally of the 9.5 mm high variant of the "2.5-inch" drive form factor, older laptops and notebooks had hard drives that varied in height, which can make it difficult to find a well-fitting chassis. Laptop optical drives require "slim" 5.25-in enclosures, since they have approximately half the thickness of their desktop counterparts, and most models use a special 50-pin connector that differs from the 40-pin connectors used on desktop ATA drives. While they are less common now than they once were, it is also possible to purchase a drive chassis and mount that will convert a 3.5-inch hard drive into a removable hard disk that can be plugged into and removed from a mounting bracket permanently installed in a desktop PC case. The mounting bracket carries the data bus and power connections over a proprietary connector, and converts back into the drive's native data bus format and power connections inside the drive's chassis. Enterprise enclosures In enterprise storage the term refers to a larger physical chassis. The term can be used both in reference to network-attached storage (NAS) and components of a storage area network (SAN) or be used to describe a chassis directly attached to one or more servers over an external bus. Like their conventional server brethren, these devices may include a backplane, temperature sensors, cooling systems, enclosure management devices, and redundant power supplies. Connections Native drive interfaces SCSI, SAS, Fibre Channel, eSATAp, and eSATA interfaces can be used to directly connect the external hard drive to an internal host adapter, without