Disk enclosure

These may also be referred to as a caddy – a sheath, typically plastic or metallic, within which a hard disk drive can be placed and connected with the same type of adapters as a conventional motherboard and power supply would use.

SCSI, SAS, Fibre Channel, eSATAp, and eSATA interfaces can be used to directly connect the external hard drive to an internal host adapter, without the need for any intervening controller.

USB or FireWire connections are typically used to attach consumer class external hard drives to a computer.

Unlike SCSI, eSATA, or SAS these require circuitry to convert the hard disk's native signal to the appropriate protocol.

iSCSI, NFS, or CIFS are all commonly used protocols that are used to allow an external hard drive to use a network to send data to a computer system.

A newer technology NAS, has been applied to some disk enclosures, which allows network ability, direct connection (e.g., USB) and even RAID features.

A 3.5-inch USB/FireWire hard disk enclosure with cover removed
An external hard drive enclosure that uses a 2.5-in drive and a USB connection for power and transfer
Simplified circuit diagrams of harddiskdrive enclosure.
Factory-assembled Buffalo external hard drive in a disk enclosure
An eSATA and Mini USB hard disk enclosure board
Multiple connectors including external power on a 2.5 inch enclosure
The PCB of an enclosure controls the data transfer, generic mass storage device drivers are readily available on most operating systems
This 2.5 inch caddy uses a single connector mini USB
Surplus enclosures following a purchase of additional storage at the Internet Archive