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A disk enclosure is a specialized casing designed to hold and power hard disk drives or solid state drives while providing a mechanism to allow them to communicate to one or more separate computers.
Drive enclosures provide power to the drives therein and convert the data sent across their native data bus into a format usable by an external connection on the computer to which it is connected. In some cases, the conversion is as trivial as carrying a signal between different connector types. In others, it is complicated enough to require a separate embedded system to retransmit data over connector and signal of a different standard.
Factory-assembled external hard disk drives, external DVD-ROM drives, and others consist of a storage device in a disk enclosure.
Key benefits to using external disk enclosures include:
In the consumer market, commonly used configurations of drive enclosures utilize magnetic hard drives or optical disc drives inside USB, FireWire, or Serial ATA enclosures. External 3.5-in floppy drives are also fairly common, following a trend to not integrate floppy drives into compact and laptop computers. Pre-built external drives are available through all major manufacturers of hard drives, as well as several third parties.
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. The exterior of the caddy typically has two female sockets, used for data transfer and power.
Variants of caddy: [9]
Advantages:
Disadvantages:
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.
In enterprise storage the term refers to a larger physical chassis. The term can be used both in reference to network-attached storage (NAS) [5] 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.
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. External variants of these native drive protocols are extremely similar to the internal protocols, but are often expanded to carry power (such as eSATAp and the SCSI Single Connector Attachment) and to use a more durable physical connector. A host adapter with external port may be necessary to connect a drive, if a computer lacks an available external port.
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. Parallel ATA and internal Serial ATA hard disks are frequently connected to such chassis because nearly all computers on the market today have USB or FireWire ports, and these chassis are inexpensive and easy to find.
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. This type of external hard drive is also known as Network-attached storage or NAS. Often, such drives are embedded computers running operating systems such as Linux or VxWorks that use their NFS daemons and SAMBA to provide a networked file 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.
"Shucking" refers to the process of purchasing an external hard disk drive and removing the drive from its enclosure, in order for it to be used as an internal disk drive. This is performed because external drives are often cheaper than internal drives of the same capacity and model, and that external drives designed for continuous usage often contain hard drives designed for increased reliability. [10]
Following the hard disk drive shortages caused by the 2011 Thailand floods, data storage company Backblaze reduced its cost of acquiring hard drives by purchasing external hard drives and shucking them. According to Backblaze Chief Executive Gleb Budman, the company purchased 1,838 external drives during this period. [11] Describing the process as "drive farming", the company noted that it was much cheaper for them to purchase 3 TB external drives and removing them from their cases manually, than it is to purchase internal drives. [12]
Parallel ATA (PATA), originally AT Attachment, also known as Integrated Drive Electronics (IDE), is a standard interface designed for IBM PC-compatible computers. It was first developed by Western Digital and Compaq in 1986 for compatible hard drives and CD or DVD drives. The connection is used for storage devices such as hard disk drives, floppy disk drives, optical disc drives, and tape drives in computers.
A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored and retrieved in any order. HDDs are a type of non-volatile storage, retaining stored data when powered off. Modern HDDs are typically in the form of a small rectangular box.
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices, best known for its use with storage devices such as hard disk drives. SCSI was introduced in the 1980s and has seen widespread use on servers and high-end workstations, with new SCSI standards being published as recently as SAS-4 in 2017.
SATA is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard to become the predominant interface for storage devices.
A laptop computer or notebook computer, also known as a laptop or notebook, is a small, portable personal computer (PC). Laptops typically have a clamshell form factor with a flat-panel screen on the inside of the upper lid and an alphanumeric keyboard and pointing device on the inside of the lower lid. Most of the computer's internal hardware is fitted inside the lower lid enclosure under the keyboard, although many modern laptops have a built-in webcam at the top of the screen, and some even feature a touchscreen display. In most cases, unlike tablet computers which run on mobile operating systems, laptops tend to run on desktop operating systems, which were originally developed for desktop computers.
The Power Macintosh G3 is a series of personal computers designed, manufactured, and sold by Apple Computer from November 1997 to August 1999. It represented Apple's first step towards eliminating redundancy and complexity in the product line by replacing eight Power Macintosh models with three: Desktop and Mini Tower models for professional and home use, and an all-in-one model for education. The introduction of the Desktop and Mini Tower models coincided with Apple starting to sell build-to-order Macs directly from its web site in an online store, which was unusual for the time as Dell was the only major computer manufacturer doing this. Apple's move to build-to-order sales of the Power Macintosh G3 also coincided with the acquisition of Power Computing Corporation, which had been providing telephone sales of Macintosh clones for more than two years.
The Zip drive is a removable floppy disk storage system that was announced by Iomega in 1994 and began shipping in March 1995. Considered medium-to-high-capacity at the time of its release, Zip disks were originally launched with capacities of 100 MB, then 250 MB, and finally 750 MB.
In computing, an optical disc drive (ODD) is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only read from certain discs, while other drives can both read and record. Those drives are called burners or writers since they physically burn the data onto on the discs. Compact discs, DVDs, and Blu-ray discs are common types of optical media which can be read and recorded by such drives.
In computer hardware a host controller, host adapter or host bus adapter (HBA) connects a computer system bus which acts as the host system to other network and storage devices. The terms are primarily used to refer to devices for connecting SCSI, SAS, NVMe, Fibre Channel and SATA devices. Devices for connecting to FireWire, USB and other devices may also be called host controllers or host adapters.
Network-attached storage (NAS) is a file-level computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. The term "NAS" can refer to both the technology and systems involved, or a specialized device built for such functionality.
ExpressCard, initially called NEWCARD, is an interface to connect peripheral devices to a computer, usually a laptop computer. The ExpressCard technical standard specifies the design of slots built into the computer and of expansion cards to insert in the slots. The cards contain electronic circuits and sometimes connectors for external devices. The ExpressCard standard replaces the PC Card standards.
In computing, Serial Attached SCSI (SAS) is a point-to-point serial protocol that moves data to and from computer-storage devices such as hard disk drives and tape drives. SAS replaces the older Parallel SCSI bus technology that first appeared in the mid-1980s. SAS, like its predecessor, uses the standard SCSI command set. SAS offers optional compatibility with Serial ATA (SATA), versions 2 and later. This allows the connection of SATA drives to most SAS backplanes or controllers. The reverse, connecting SAS drives to SATA backplanes, is not possible.
The USB mass storage device class is a set of computing communications protocols, specifically a USB Device Class, defined by the USB Implementers Forum that makes a USB device accessible to a host computing device and enables file transfers between the host and the USB device. To a host, the USB device acts as an external hard drive; the protocol set interfaces with a number of storage devices.
In computing, external storage refers to non-volatile (secondary) data storage outside a computer's own internal hardware, and thus can be readily disconnected and accessed elsewhere. Such storage devices may refer to removable media, compact flash drives, portable storage devices, or network-attached storage. Web-based cloud storage is the latest technology for external storage.
A SCSI connector is used to connect computer parts that communicate with each other via the SCSI standard. Generally, two connectors, designated male and female, plug together to form a connection which allows two components, such as a computer and a disk drive, to communicate with each other. SCSI connectors can be electrical connectors or optical connectors. There have been a large variety of SCSI connectors in use at one time or another in the computer industry. Twenty-five years of evolution and three major revisions of the standards resulted in requirements for Parallel SCSI connectors that could handle an 8, 16 or 32 bit wide bus running at 5, 10 or 20 megatransfer/s, with conventional or differential signaling. Serial SCSI added another three transport types, each with one or more connector types. Manufacturers have frequently chosen connectors based on factors of size, cost, or convenience at the expense of compatibility.
A solid-state drive (SSD) is a type of solid-state storage device that uses integrated circuits to store data persistently. It is sometimes called semiconductor storage device, solid-state device, and solid-state disk.
Target Disk Mode is a boot mode unique to Macintosh computers.
This glossary of computer hardware terms is a list of definitions of terms and concepts related to computer hardware, i.e. the physical and structural components of computers, architectural issues, and peripheral devices.
In computing, eSATAp is a combination connection for external storage devices. An eSATA or USB device can be plugged into an eSATAp port. The socket has keyed cutouts for both types of device to ensure that a connector can only be plugged in the right way.
Hard disk drives are accessed over one of a number of bus types, including parallel ATA, Serial ATA (SATA), SCSI, Serial Attached SCSI (SAS), and Fibre Channel. Bridge circuitry is sometimes used to connect hard disk drives to buses with which they cannot communicate natively, such as IEEE 1394, USB, SCSI, NVMe and Thunderbolt.