USB and IEEE 1394 Guide
As described in our External Hard Drive buying guide, the USB and IEEE 1394 ports (also
known as FireWire) are mainstream interfaces for the connection of computer peripherals and
devices. What are the advantages of these interfaces and how do we go about recognizing
them? Let’s find out.
USB
What is USB?
The USB (Universal Serial Bus) I/O interface standard is usually featured on computer
peripherals and handheld digital devices. The latest revision of this standard is USB 2.0 and
the majority of external hard drives utilize one or more USB 2.0 interfaces.
Benefits of USB:

Hot-pluggable: you can plug or unplug an external hard drive while your computer is
running. Shutting down or restarting your computer to connect or disconnect your USB
peripheral is not required.

Outstanding cross-platform performance: USB can be used on both the Mac and PC.
The older USB 1.1 specification operates at 1.5 Mbps in Low-Speed mode and 12 Mbps
in Full-Speed mode. With USB 2.0 support, the USB interface provides 480 Mbps
bandwidth in Hi-Speed Mode to greatly improve interface performance.

Backwards compatibility: USB 2.0 compliant external hard drives will work on
computers that are equipped with only USB 1.1. Although transfer speeds are limited to
USB 1.1 spec, however. The USB 1.1 and USB 2.0 ports utilize the same port
mechanism.

Provides power to your peripherals: The power provided by the USB bus is sufficient to
power certain small form factor external hard drives, e.g. 1-inch and 1.8-inch products.
These external hard drive solutions are extremely portable, especially without an AC
adapter to carry around.
USB port types on external hard drives
There are three types of USB connectors often found on external hard drives: series “A”,
series “B” and mini-USB.

Series “A” connector: The series “A” USB connector is often offered in the form of a
plug on small form factor (especially 1-inch) external hard drives. All you need to do is
simply connect it to a USB port on your computer as computers today typically provide the
series “A” receptacle/port as standard.
USB series “A” plug on an external hard drive

Series “B” connector: 3.5-inch external hard drives will typically provide one USB series
“B” receptacle. You need to use a USB cable (commonly bundled as an accessory)
featuring a USB series “A” plug on one end and a series “B” plug on the other to connect
the external hard drive to a USB port on your computer.
USB series “B” receptacle on an external hard drive

Mini-USB connector: This connector is very common on 1.8 and 2.5-inch external hard
drives. To connect these drives to your computer, please use a USB cable (commonly
bundled as an accessory) featuring a USB series “A” plug on one end and a Mini-USB
plug on the other end.
Mini-USB receptacle on an external hard drive
IEEE 1394
What is IEEE 1394?
Like USB, IEEE 1394 too is a high-speed serial I/O technology that can be found on many
peripheral devices. IEEE 1394 goes by a few other names, such as FireWire (Apple), and
i.Link (Sony).
There are two IEEE 1394 standards in use today:
1. IEEE 1394a offering 400 Mbps bandwidth;
2. IEEE 1394b offering double the bandwidth of IEEE 1394a currently, and capable of
supporting up to 3.2 Gbps in the future;
Both IEEE 1394a and IEEE 1394b are used on external hard drives.
Benefits of IEEE 1394

Cross-platform performance: as mentioned above, both IEEE 1394a and IEEE 1394b
offer fast transfer speeds, especially the latter. In addition, IEEE 1394 provides sustained
fast data transfer rates, making it extremely suitable for frequent large data transfers often
seen in digital video and audio devices and graphics applications. IEEE 1394 is supported
by both the Mac and PC.

Hot-pluggable: IEEE 1394 also supports hot-plugging. To use an IEEE 1394-enabled
external hard drive, just connect it to a running computer.

Backward compatible: IEEE 1394 is designed to be backward compatible, meaning that
an IEEE 1394b-equipped external hard drive can be connected to the IEEE 1394a port of
a computer, and vice versa. As IEEE 1394a and IEEE 1394b ports utilize differing port
designs, it is necessary to use the right adapter cable.
IEEE 1394 port types on external hard drives
There are three types of IEEE 1394 ports available: 4-pin, 6-pin and 9-pin. The 4-pin and 6-pin
ports are compliant with IEEE 1394a, and the 9-pin port supports IEEE 1394b.
4-pin: The 4-pin port is favored by small form factor external hard drives thanks to its thin and
small profile. Please note that the 4-pin IEEE 1394 port does not supply power, thus an
alternate power source is required. To connect a 4-pin IEEE 1394-equipped external hard
drive to the computer, use a 6-to-4-pin IEEE 1394 cable as computers typically often offer
6-pin ports.
4-pin IEEE 1394 receptacle on an external hard drive
6-pin: 6-pin IEEE 1394 ports are frequently used on 2.5” and 3.5” external hard drives. The
6-pin IEEE 1394 port also provides power to the connected device. As a result, an alternate
source of power is unnecessary on certain external hard drives equipped with the 6-pin IEEE
1394 port. A 6-to-6 pin cable is needed to connect these external hard drives to the computer.
6-pin and 9-pin IEEE 1394 receptacles on an external hard drive
9-pin: Currently the fastest IEEE 1394 port, it is often used on high-end external hard drives.
The 9-pin IEEE 1394b port it is physically smaller than the 6-pin port and isn’t used very widely
at the moment. In addition, and you may need a 9-to-6-pin IEEE 1394 cable for connection to
your computer, which may only provide IEEE 1394a 6-pin ports.