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A hardware dongle is a small, portable device that interfaces with a laptop or desktop computer, typically with the Universal Serial Bus (USB) port. Sometimes resembling a flash drive, it was traditionally used as a security key designed to authorize the use of certain software packages, or to allow the holder entrance into a Virtual Private Network (VPN). Today, the term also refers to pigtail-type adapters, to wireless network adapters, and even to common flash drives, though the latter usage is not universally accepted.
Software that requires a dongle will not run without the device present, or it might run in crippled mode. The device can authorize or unlock particular features of the software in accord with the type of license purchased. In addition to providing security, it is more difficult to crack a dongle or pirate it than it is to copy or crack software. Requiring both the software and matching hardware increases the difficulty of piracy to such a degree that it essentially makes the product a less desirable target.
A hardware dongle is also used with many VPNs, issued to authorized employees. The device exchanges security tokens with the VPN in the handshake process, providing stored, encrypted credentials before the computer is allowed access to the network. The dongle is typically mated to a particular computer through unique profile identifiers, disallowing it to be operated on an unknown system should it be lost or stolen. A secure password is also commonly required of the user, further deterring unauthorized use.
A pigtail dongle or adapter translates the data flow from one type of port to another. For example, an ExpressCard®-to-USB dongle allows a laptop or desktop that does not have an ExpressCard® slot to use such a device by inserting it into an external port, pigtailed to a USB connector that can be attached to the computer.
Other pigtail dongles are 2-in-1 adapters. One example is the HDMI 2x1 Auto-Switching dongle. This adapter has a male HDMI connector for plugging into a high-definition TV (HDTV) or home entertainment receiver. The other end features two female HDMI ports for incoming signals from two separate devices, such as a DVD player and game console. The cable senses which of the devices is active, displaying the signal on the HDTV. This dongle is handy for receivers or for HDTVs with limited inputs.
Another type of hardware dongle is the wireless network adapter. There are several types of these devices for connecting to either a Bluetooth® network, a wireless local area network (WLAN), or to a cellular or mobile network.
Bluetooth® is a wireless personal area network (PAN) that is used primarily for connecting personal devices over short distances. A Bluetooth® dongle will allow a laptop to trade data with a cell phone, for example, or with other Bluetooth®-enabled devices, including printers and fax machines.
WLANs are typically found in the home and office and most computers today have wireless network cards built-in. When an internal card cannot be used, an external wireless adapter or wireless hardware dongle can be purchased. The dongle must share a common wireless protocol with the router it will be connecting to.
Mobile connectivity was previously associated solely with handheld portable devices such as cell phones and personal digital assistants. The popularity of cellular broadband is growing as an alternative for laptop connectivity, however. Since a cellular dongle must be branded by or compatible with the carrier of the cellular service the user wishes to connect to, the service is chosen first, then a dongle can be selected.
A common flash drive might also be referred to as a hardware dongle, though some do not consider these true dongles because they do not translate data streams between port types, nor are they security keys in the strict sense, even when adapted for use as such. Other types of adapters commonly referred to by this term also fall short of this stricter definition, such as the 2-in-1 HDMI adapter/dongle.
The Bluetooth dongle is one of the most convenient things ever invented. They are cheap and reliable -- keep that in mind should you be looking at a computer that doesn't have Bluetooth already installed but can be added as an expensive option. A cheap, reliable dongle could save you a few bucks.