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A Brief Lesson On Interfaces

Storage and Security On the Go: 6 External Hard Drives
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Now that parallel and serial ports are known as "legacy interfaces" and are gradually becoming obsolete, the USB (Universal Serial Bus) interface is taking over. USB was developed many years ago, and is noted for being cheap to implement and easy to use. USB 1.1 can handle up to 12 MBit/s, i.e. theoretically 1.5 MB/s. In real life, however, you can only achieve around 1 MB/s. This makes it fast enough for small peripherals like keyboards, but not for storage devices.

USB 2.0 was developed to provide more flexibility for USB, especially for applications such as mass storage. All PC systems available today support USB 2.0, which increases bandwidth from 12 Mbit/s all the way to 480 MBit/s, or 60 MB/s. Real-world throughput is usually only just under 30 MB/s, but this is still more than enough for most newer external devices.

Users who want more speed can avail themselves of one of the two FireWire (IEEE-1394) interfaces. The protocol is isochronous and therefore particularly suitable for transmitting data in real time - that is why many video devices feature FireWire, or the Sony version, i.LINK. The latter is technically identical but doesn't come with its own power supply, making it especially popular for notebook owners who don't want to empty their batteries with an external device.

Interestingly, even though the 400 MBit/s number is lower than USB 2.0's 480 Mbit/s, FireWire interfaces are almost always faster in practice than USB 2.0 interfaces. FireWire units often achieve transfer speeds above 30 MB/s, although in theory USB 2.0 should be faster.

FireWire 800 is faster still and can enable speeds of 60 MB/s. This is necessary if you want to operate an external storage device without slowing the data transfer speed. Serial ATA devices pose the only alternative, but so far these still require a proprietary interface.

Interface Theoretical bandwidth Actual bandwidth
USB 1.1 (old) 12 MBit/s 1 MByte/s
USB 2.0 480 MBit/s 25 MByte/s
IEEE 1394A / FireWire400 / i.Link 400 MBit/s 30 MByte/s
IEEE 1394B / FireWire800 / i.Link 800 MBit/s 60 MByte/s
Serial ATA 1500 MBit/s 120 MByte/s
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