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CHIPS Articles: FireWire versus USB

FireWire versus USB
By Patrick Koehler - January-March 2001

If you have purchased a new personal computer (PC) recently, your system is probably USB-ready. This means that your PC is Universal Serial Bus (USB) compliant. This is important because it lets you use your PC and peripherals in some very valuable new ways. With USB, a user can connect peripherals, such as a digital joystick, scanner, digital camera, or a PC telephone instantly to a computer.

Before USB connection, a user, who wanted to add a device had to first determine which port to use, install an add-in card and set DIP (Dual-in-line package) switches and configure interrupt Request Queue (IRQ) settings. USB replaces all the different kinds of serial and parallel port connectors with one standardized "plug and port combination."

With USB-compliant PCs and peripherals, you just plug them in and turn them on or "plug and play!" USB makes the whole process automatic without the excruciating process of add-in cards, DIP switch settings or IIRQs.

Another timesaving USB feature is called "hot-swapping", which means you won't need to shut down and reboot your PC to attach or remove a peripheral. This feature is a favorite with users who participate in multi-player games, as well as business and notebook PC users who share peripherals. Most computers come with two USB ports but you can purchase USB peripherals, known as USB hubs, which have additional ports so you can "daisy chain" multiple peripherals together.

To achieve optimum performance speed, make sure you purchase a powered hub. This is because USB powered hubs can distribute electrical power to peripherals. USB lets the PC automatically determine the power required and delivers it to the device. USB connections allow data to flow both ways between the PC and device. An example of this is: a PC could automatically manage a telephone call center to maintain voice, fax and data mailboxes and perform a variety of other functions. For users who are interested in the current trend of entertainment for the PC-your PC can tune a set of USB-compliant stereo speakers.

Currently USB 1.0/1.1 devices run at a speeds of 1.2/1.5Mbps to 12Mbps. USB 2.0 version was approved for release at the Windows Hardware Engineering Conference (WinHEC) in New Orleans, Louisiana, in April 2000. This updated technology specification increases the data connection from 12Mbps on USB 1.1 up to a maximum speed of 480Mbps.

Compaq, Hewlett-Packard, Intel, Lucent, Microsoft, NEC and Philips Semiconductors jointly developed the technology. USB 2.0 enables high-performance PCs and user applications to be more productive. For example, scanners can create a high-resolution digital image in seconds, versus minutes on USB 1.1. Users will be able to back up a gigabyte of data in less than a minute on USB 2.0 in comparison with about a half-hour on USB 1.1.

Connectivity is being further advanced with the IEEE 1394 standard. USB 2.0 and 1394 primarily differ in terms of application focus. The USB 2.0 Promoter Group expects USB 2.0 to be the preferred connection for most PC peripherals while the principal market for IEEE 1394 will be audio/visual (AV) consumer electronic devices, such as digital camcorders, digital videocassette recorders (VCRs) and digital televisions. Most likely both USB 2.0 and 1394 will be available on many consumer systems in the future.


Originally invented by Apple and adopted as the IEEE 1394 standard in 1995. It simplifies cabling and supports transfer speeds of up to 400Mbps. Firewire is integrated into all Power Mac G4 computers, PowerBooks and iBooks. Like USB, FireWire speeds up the multimedia data and large files and enables easy connection of digital devices, including cameras, video tapes, video disks, set-top boxes, and music systems.

FireWire is a small, thin serial cable, replacing bulky and expensive interfaces. Like USB, it is "hot pluggable"-peripherals can be added and removed while the bus is active. It is easy to use and flexible, and like USB supports daisy chaining. It also allows branching for peer-to-peer connection.

FireWire supports both asynchronous and isochronous data transfers. Asynchronous data transfers support traditional memory-mapped, load and store applications. FireWire's ability to support isochronous data channels enables guaranteed data transfer at a specified rate. This is an attractive feature for multimedia applications where uninterrupted transfer of time-critical data and just-in-time delivery reduces the requirement for costly buffering.

FireWire is an excellent choice as the digital interface for consumer electronics and AV devices. As a peer-to-peer interface, it allows interface between camcorders without a computer. Like USB, it also allows multiple computers to share a peripheral without any special support in the device or computer. Industry forecasters predict that consumer electronics and computers will continue to come together.

FireWire takes the complexity out of connecting Small Computer Serial Interface (SCSI or "scuzzy") based mass-storage devices by using the Serial Bus Protocol-2 (SBP-2). This protocol allows for high-speed data transfer and will eventually scale up to the speed of the FireWire itself. FireWire has the bandwidth capability to replace and consolidate most of today's peripheral connection communications methods.

FireWire is not really a popular choice for PCs, whereas USB is the popular low-cost choice for PC connections.

Patrick Koehler is a member of the IT Umbrella Program Team. He holds a Bachelor of Science degree in computer information systems.

The views expressed here are solely those of the author, and do not necessarily reflect those of the Department of the Navy, Department of Defense or the United States government.

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