A hard drive has a plurality of concentric tracks for storing data. Each track has a plurality of sectors. Some hard disk drives contain several hard disks, each hard disk being horizontally mounted on one shared vertical spindle-axis, so that the hard disks form a stack of hard disks. The hard disk drive includes a magnetic read/write head which flies above the surface of the hard disk while the hard disk is rotating. A head actuator locks all the heads together so that all heads are at the same position from the center of the disk along a given radius. A hard drive relies upon mechanical actions such as rotation of a disk or movement of a magnetic head for reading and writing data. A hard disk drive includes one or more randomly accessible rotatable storage media, or disks upon which data is encoded. The data is encoded as bits of information using magnetic field reversals grouped in tracks on the magnetic hard surface of rotating disks. A transducer head supported by an actuator arm is used to read data from or write data to the disks. A voice control motor (VCM) attached to the actuator controls positioning of the actuator, and thus the transducer head position over a disk. Data read from the disk or written to the disk is provided through circuitry to a processor. Servo position data read from the disk is processed by the processor, enabling the processor to provide servo current command signals to control the VCM for proper positioning of a transducer head relative to a disk. The read/write heads may move from at least an inner diameter to an outer diameter of each platter where data is stored. This distance may be referred to as a data stroke. Hard disk drives also include a variety of electronic circuitry for processing data and for controlling its overall operation. This electronic circuitry may include a preamplifier, a read channel/write channel circuit, a servo controller, a motor control circuit, a read-only memory (ROM), a random-access memory (RAM), and a variety of disk control circuitry to control the operation of the hard disk drive and to properly interface the hard disk drive to a system bus, and voltage regulators to supply voltages needed other than the ones from the power plug.

A hard drive is typically disposed on a carrier assembly, and the carrier assembly is inserted, via a guide rail system, into a bay in a computer chassis. The hard drive carrier accommodates a hard drive and mechanically mates with a drive bay in a computer chassis.  An electromagnetic energy interference (EMI) shield is sometimes a part of a carrier assembly and functions to shield the hard drive from any EMI interference. The actuator arm, motor and other components of a typical disk drive unit are relatively small and fragile, and are therefore susceptible to damage when subjected to excessive external shock loads or vibration. For this reason, hard disk drives are typically rigidly mounted to the housing of the computer system by screws or other fastening means. In a notebook computer, the hard disk drive is conventionally installed in the base housing of the computer by horizontally inserting the disk drive inwardly through an external housing side wall until an electrical connector on the inner end of the disk drive is removably mated with a corresponding electrical connector. In general, the hard disk drive cannot be removed from the computer unless the enclosure is disassembled. A primary function of the hard disk drive is to receive data from the associated computer system, write the data onto the hard disk without loss of the data, and then read and transmit the data to the computer system when necessary. Therefore, a manufacturer of the hard disk drive not only makes an effort to maximize data recording capacity, but also looks for various means to prevent data loss when writing and reading the data. Hard disk drives contain programs and other information that are vital to the user. It is sometimes desirable to transfer such information to a different computer system. Transferring programs from a hard disk typically requires loading the information onto storage devices. Such methods can be time consuming, particularly if the program is long or there is a large amount of data. Additionally, removing an HDD from most computer systems today requires tools and involves pulling 25 to 50-pin cables from cable sockets. Overtime, or through incorrect usage, these cables or sockets become frail and can introduce data transfer errors associated with the HDD in use. Furthermore, a computer data center (also referred to as an Internet data center or an enterprise data center) may contain a myriad of computer systems utilizing various hard drives. The large number of high-capacity HDDs in a data center poses significant problems associated with their removal and installation.

Accordingly, it is becoming extremely important for various reasons (such as data backup and generally switching hard drives) to be able to easily, quickly, and efficiently remove and install a hard drives in a computer system. Today's personal computer systems provide users with a high degree of flexibility in terms of the number of peripheral devices that may be connected to a given system. Users are generally able to connect additional internal and external peripheral devices to meet the storage or data access demands required to complete the user's job. Portable external hard drives have been developed to work with the hard drive built in the computer, which dramatically increases the convenience to the user. A portable hard disk drive provides convenient access to data stored therein through a signal cable assembly. A removable external hard drive allows a plurality of users to each have a separate hard drive with the respective user's applications and data. In this manner, multiple users each having their own drives can effectively share a single computer system. A removable hard drive also allows a single user to store a greater number of applications and data for use in the computer system than would otherwise be available with a single non-removable hard drive. External hard drive solves the problem of connecting a drive to a computer without opening up the computers. The external hard drives attach to a computer via one of the common I/O ports on a computer: USB, firewire or PCMCIA. The external hard disk drive typically has the same structure as that of a hard disk drive internally mounted in the computer. Generally, an external hard disk consists of shell in which is allocated a USB transmission interface for connected to a memory module, whereby universal serial bus (USB) connector of said USB transmission interface stands out from one side of shell and is protected by cover. The main unit of the hard disk drive is covered with a metal sheet to control EMI, and is then housed in a case fabricated of a resin. When a hard drive system is intended to be mobile, and includes an internal battery, the system is typically set to operate at a low power level.