External hard drive
An external hard disk is a hard disk drive that can be connected directly to a computer via an interface such as USB , FireWire , eSATA , Thunderbolt or as a removable disk drive . There are also external hard drives that can be connected to a network with a LAN cable or wirelessly via WLAN , see Network Direct Attached Storage (NAS).
The drives of external hard drives are identical to internal hard drives. They are connected via converter electronics ( host bus adapter ) for connection with the common external interfaces. A housing is used to protect against damage caused by electrostatic discharges and, to a very limited extent, to dissipate heat.
HDD and SSD
Below are just be hard drives ( English hard disk drive , abbreviation HDD described) where the data is stored on rotating, magnetic metal disks. This must be distinguished from solid-state drives , abbreviation SSD , which are an immovable block. Both are translated in German with the word hard disk . In terms of data security, interfaces and power consumption, both are equivalent. The SSDs are less sensitive to vibration, quieter and faster, but cost a lot more than the HDD, so that they are hardly used in the field of external hard drives.
Sizes of the HDD
Hard disk drives with a form factor of 3.5 inches measure around 10 cm × 15 cm × 2.5 cm. External hard drives with such drives are accordingly somewhat larger. An additional power supply unit is required due to the power consumption.
The smaller 2.5-inch hard drives are approximately 7 cm × 10 cm. The height depends on the capacity and varies between 5 and 15 mm. 2.5-inch hard drives do not need their own power supply , but are supplied with power via suitable connections such as USB or FireWire. Therefore, they are particularly suitable for transporting data (see also sneaker network ).
The 1.8-inch format, which is still used today in part for external SSDs that work with electronic memory modules instead of rotating magnetic disks , is less common . The 1.0-inch format has been replaced by USB sticks .
There are also external hard drive enclosures with two or four hard drives. These can work for a higher data transfer rate in the RAID- 0 network or for greater data security in the RAID-1 network.
Accident-proof data memories exist for particularly secure data storage .
Connection types
External hard drives can be connected to other devices via various interfaces. The most common is the connection via USB . The two USB versions 2.0 and 3.0 are basically compatible with each other, but the usable data rate for USB 2.0 is in the order of 40 MB / s, while with USB 3.0 around 300 MB / s can be achieved.
With both USB versions, a 2.5-inch hard drive can be supplied with power via the interface. With USB 2.0, the maximum current is limited to 500 mA, which is why some manufacturers of external hard drives supply Y-cables with which the current of a second USB port can be used. With USB 3.0, the current was increased to 900 mA, with which practically any 2.5-inch hard drive can be operated.
Power can also be supplied via the bus when connecting via FireWire or Thunderbolt . However, the data rates that can be achieved with FireWire 400 and 800 are below those of faster hard disks, so that this interface also represents a bottleneck in transmission. Thunderbolt, on the other hand, is fast enough to also access external SSDs at full speed.
The eSATA connection, which is no longer in use , made the SATA bus system, which is common with hard disk drives, also available for external devices. This means that an external hard drive via eSATA works at the same transfer rate as an internal hard drive that is connected to SATA. However, no power supply can be provided via eSATA, so that corresponding external hard drives require power from a power supply unit or a USB port.
Power supplies
3.5-inch IDE / PATA hard drives usually require 5 and 12 V operating voltage. In the beginning, the external power supply units used for the supply provided these two voltages. However, each manufacturer used their own connector to connect to the hard drive. Mostly, mini-DIN connections with four, five or six pins were used. The pin assignments also differ, so that an incorrect power supply unit can, in the worst case, destroy the connected hard disk due to overvoltage or polarity reversal , despite the mechanically matching plug . Since the 2010s, power supplies with only one voltage and a barrel connector have been used (mostly 12 V). The 5 V required are generated in the device by a voltage converter .
Encryption
The stored data or the entire data memory of a hard disk can be completely or partially encrypted using software or hardware-based hard disk encryption. This applies to internal and external hard disks, but is particularly important for external hard disks in order to prevent unauthorized data access in the event of loss.
Individual evidence
- ↑ 2.5-inch and external hard drives - www.gnir.ch ( Memento of the original from December 20, 2008 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Benjamin Benz: Fast as an arrow - the third USB generation delivers transfer rates of 300 MB / s. In: c't . No. 22, 2008, p. 212.
- ↑ Connections for external hard drives | Hardware bulkheads. www.HardwareSchotte.de, accessed on November 1, 2013 .
- ↑ Firewire and USB - www.powermacintosh.de
- ↑ Thunderbolt in the practical test: Up to 825 MByte / s | CHIP. (No longer available online.) In: chip.de. September 15, 2011, archived from the original on March 9, 2014 ; Retrieved November 1, 2013 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ eSATA - external SATA | Electronics Compendium. www.elektronik-kompendium.de, accessed on November 1, 2013 .
- ↑ Various external power supplies with plugs
