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Get on the BUS
USB and FireWire will change the way you work forever. Hook up dozens of peripherals in a flash and get ready for a new level of performance.

-- by Lenny Bailes

The Pentium MMX has hogged the PC hardware spotlight in recent months, but two other technologies are emerging that could make using PCs easier than ever. And it should come as no surprise that Intel and Microsoft are actively involved in ushering in these technologies. The Universal Serial Bus (USB) and the IEEE 1394 (also known as "FireWire") peripheral interface may prove to be the most important developments in Windows PC technology since the introduction of the PCI bus. They may not have generated the same kind of ballyhoo as Intel's flashy MMX rollout, but they just might have as much, if not more, influence on changing the essential architecture of PCs.

There's little doubt that USB and IEEE 1394 will become standard fare in both business and home computers, but for now-and some months to come-you must carefully consider whether the systems and peripherals you're about to purchase will support these bus technologies.

You need to know what USB and IEEE 1394 are all about: how they work, the performance gains and ease-of-use benefits they promise, and the availability of compliant PCs and peripherals.

Two Bus Routes

Overall performance of a Windows PC is more likely to be affected by the machine's bus architecture and motherboard design than by the efficiency of its CPU. The 32-bit Video Electronics Standards Association (VESA) and PCI bus standards represented significant advances in computer technology, allowing Windows to juggle disk I/O and high-bandwidth video data more effectively. The ease-of-use features that Windows 95 brought to the peripheral realm-specifically with its Plug-and-Play hardware interface standard-complemented the performance enhancements of 32-bit bus design.

Anyone who's been using Win95 for a while knows that the implementation of PnP is far from perfect, yet it is a solid first step toward addressing one of the thorniest issues of Windows computing. Adding hardware is generally far easier than it used to be, but the physical installation of hardware peripherals-even with PnP-can still be something of an ordeal. You have to open the computer case, slide cards in and out of expansion slots and often tinker with DIP switches that seem designed to make even the nimblest hands feel oversized and clumsy.

The Universal Serial Bus was originally conceived by a seven-member consortium consisting of Compaq Comuter Corp., Digital Equipment Corp., IBM PC Co., Intel Corp., Microsoft Corp., NEC and Northern Telecom. The original concept has since been expanded, and a large number of computer and peripheral manufacturers have given their support to the bus standard. USB is designed to put an end to the roll-up-your-sleeves-and-get-under-the-hood school of peripheral installation and configuration. It combines the best features of SCSI architecture with an advanced PnP standard. If USB delivers as advertised, you won't have to worry about bus slots, IRQs or poking around your PC to find space for a new port.

What's more, a single USB port will support a slew of external peripherals-up to 127-such as keyboards, monitors, scanners, modems, video cameras and digital telephones. When you connect a new device, Windows will recognize and install it on the fly-without even rebooting the computer. USB allows for both low- and high-speed data paths of 1.5Mb per second and 12Mbps.

The IEEE 1394 standard is named for the group that defined it, the Institute of Electrical and Electronic Engineers. Apple Computer and Texas Instruments, the companies involved in the IEEE 1394 interface's primary development back in the '80s, dubbed it "FireWire." Some view IEEE 1394 as competition for USB, but in fact, the two buses can coexist and complement each other in a single system, in a manner similar to today's parallel and serial ports. Bill Gates has described FireWire as a key technology that will help put the PC in the nucleus of a home entertainment center-but this does not mean Microsoft intends to deviate from its support of USB.

IEEE 1394 isn't as far along in development as USB, but support for the standard-in addition to that already pledged by Microsoft, Apple, Texas Instruments and Intel-is widespread. Among the manufacturers already in the FireWire camp are Adaptec, Sony and Compaq. A number of other companies, including Cirrus Logic and Western Digital Corp., have issued statements of intent to cooperate with IEEE 1394.

FireWire provides high-bandwidth, high-speed data transfers in excess of what USB offers. It can support data-transfer speeds from 100Mbps to 400Mbps-roughly four times as fast as a 100BaseT Ethernet connection and far faster than USB's 1.5Mbps or 12Mbps per second speeds. Its high-speed capability makes FireWire viable for connecting digital cameras, camcorders, printers, televisions, network cards and mass storage devices to your computer. The current implementation of the standard supports up to 63 devices on a single bus.

Take a Bus Tour

All peripherals connected via a USB interface are managed by a USB host controller mounted on the PC's motherboard or on a PCI add-in card. The host controller and subsidiary hub controllers manage USB peripherals, helping to reduce the load on the PC's CPU time and improving overall system performance. In turn, USB system software installed in the operating system manages the host controller.

Microsoft has issued an OEM USB service supplement to Windows 95 and plans to incorporate full USB support in future releases of Windows 9.x and Windows NT, although timing remains an unknown factor. (See sidebar "Missing in Memphis?")

Data on the USB flows through a bidirectional pipe regulated by the host controller and by subsidiary hub controllers. An improved version of "bus mastering" allows portions of the total bus bandwidth to be permanently reserved for specific peripherals; this is called isochronous data transfer.

USB's bandwidth of 12Mbps is much higher than current serial connections (115.2Kbps) allow. You can daisy-chain up to 127 peripherals to one another using USB's simple rectangular cable connectors or plug them into a multiported hub controller. The maximum cable length for USB is 5 meters. Hub controllers will be available as separate units and will also be incorporated into larger peripherals, such as monitors and printers.

In addition to offering the convenience of PnP with support for hot-swapping, USB is source-terminated, so you don't have to worry about device termination issues as you add or remove peripherals. When you connect a new device, the USB hub controller queries the device for a vendor ID and the operating system chooses an appropriate device driver. USB further simplifies peripheral handling by using a single IRQ, port address and DMA channel.

What USB doesn't offer is the high-bandwidth data transfer required by such data-hungry devices as digital cameras/camcorders, high-speed printers, network cards and mass storage devices. But in addition to the devices mentioned earlier, USB should be able to handle light-workload printers and low-bandwidth cameras used in videoconferencing.

USB-enabled devices are beginning to trickle into the market, and many more should appear in the coming months. With widespread acceptance among manufacturers, there's little to impede the USB's progress. The standard is very inexpensive to implement in systems, and the components cost less to manufacture than do equivalent PCI components. (No precise figures were available at press time.)

IEEE 1394 and USB have similar architecture and goals-move more data and service more devices-but they differ when it comes to transfer rates and capacity. IEEE 1394's higher data-transfer capability makes it ideal for digital cameras, camcorders and high-speed printers, as well as DAT grade audio and cable modems. Devices can be daisy-chained and managed via a single port address, IRQ and DMA channel. The IEEE 1394 cable can supply up to 1.5 amps of DC power to keep attached devices "alive" when they're powered down. And your computer doesn't have to be turned on to manage some FireWire peripherals; for example, a VCR can control a camcorder, TV set or audio receiver that's connected to the bus.

IEEE 1394 also supports PnP, automatically recognizing new devices and allowing the computer to reconfigure itself when the devices are removed. It does not, however, use additional external hub controllers, as USB does. The current IEEE 1394 specification supports data transfers of 100Mbps, 200Mbps or 400Mbps. The "1394-b" standard currently under development will extend that bandwidth to 800Mbps-or higher. Like USB, IEEE 1394 supports reserved bus bandwidth for specified peripherals (isochronous transfer) as well as bulk data transfer. Isochronous data transfer ensures that video or audio playback and recording won't suffer random degradation when some other peripheral makes a sudden demand on the bus.

FireWire uses a six-conductor cable (up to 4.5 meters long) that contains two twisted-pair transmission lines, two power conductors and a shield. The design resembles a standard 10BaseT Ethernet cable. Some consumer FireWire devices from Sony use a nonstandard variant of the cable that doesn't contain the power conductors; these devices require an additional power adapter. Most future devices will use the standard six-wire IEEE 1394 connector and provide special adapter cables to incorporate nonstandard devices. Members of another IEEE standards committee are also working on designs for IEEE-1394 bridges that can connect multiple FireWire node clusters.

On the Software Side

Although the retail version of Windows 95 does not currently include support for USB devices, Microsoft's OEM Service Release (OSR) 2.1 provides USB operating system support as well as several peripheral drivers. Unfortunately, the Win95 OSR is only available on new PCs. Microsoft is in the process of changing its API model for Windows device drivers so that a single code module can be used for both Windows 9.x and Windows NT. Several drivers written to the new Windows Device Model (WDM) standard are already present in the Windows 95 OSR 2.1. Currently, there are no operating system-level additions for USB in the Windows 9.x NT Control Panel, but in the future, individual peripheral manufacturers may provide supplements that let users regulate display screen settings, power management and so forth. Some of these controls may also appear in a hardware format on standalone or peripheral-mounted hub controllers.

Microsoft announced its support for the IEEE 1394 bus in early 1996. Microsoft and Sony Electronics signed a letter of intent to develop open device driver interfaces, APIs and an open host controller interface for IEEE 1394. Several companies plan to assist Microsoft and third-party USB/IEEE 1394 hardware vendors by marketing driver development kits and by designing custom drivers for specific peripherals. Paul Lever, president of BlueWater Systems, which publishes the WinDK Device Driver Development Kit, says he believes the implementation of USB and IEEE 1394 standards in Intel-based PCs will significantly lower the current barriers-such as PnP problems and the lack of drivers-to attaching new hardware to Windows NT.

More Bus Business

USB computers are here now, with systems available from such noted vendors as Compaq, DEC, IBM PC Co., Sony and Toshiba. Separately sold motherboards and clone systems with onboard support for USB are also available as of this writing. Since April 1996, all motherboards based on Intel 430VX and 430HX chipsets have USB host controllers. If your system has one of these USB-enabled motherboards, the only obstacles you face may involve obtaining the physical USB connector that plugs into the header on the motherboard and getting a copy of the Windows 95 OSR 2.1 that supports USB.

Several motherboard manufacturers we interviewed said the connectors needed to hook up USB peripherals should be available later this year. We were able to locate one motherboard vendor, ASUS Computer International, that currently stocks connectors for its USB-enabled motherboards. Owners of systems with ASUS motherboards can order the connector for $10.

Some examples of USB peripherals that are currently shipping (or about to) include the Top Gun joystick from ThrustMaster; Alps Electric and Keytronics keyboards; a TAPI-compliant telephone from Mitel Corp.; the ScanMan color scanner and a mouse from Logitech; and the Xirlink Visionlink videophone, a digital camera that's designed for videoconferencing.

IEEE 1394 has not yet approached USB's market penetration, and only a few devices and systems are available. Toshiba and Texas Instruments have 1394-enabled notebook computers. Sony's DCR-VX700 DV camcorder has a front-panel FireWire connector, and Panasonic has added FireWire support to its line of professional broadcast TV editing decks. Microsoft's support for this interface may or may not appear in 1997 upgrades to the Windows operating system, but will definitely show up in subsequent releases.

Support for Older PCs

There's a lot of good news about USB and IEEE 1394, but maybe the best news is that you don't have to trash your current system to take advantage of these technologies. In most cases, you'll be able to add USB and IEEE 1394 support using special adapters manufactured by third-party vendors.

CMD Technology, a well-known manufacturer of IDE controller peripherals, is currently marketing the CSA-6700 PCI-to-USB controller board. This is an inexpensive card that plugs into a PCI slot on any 486/Pentium motherboard and allows the computer to handle USB peripherals. The CSA-6700 includes software drivers that integrate with Microsoft's OEM USB release of Windows 95.

Adaptec is shipping the AHA-8940 PCI-to-IEEE 1394 host adapter, which supports up to 63 FireWire devices through one internal and two external connectors at speeds of up to 200Mbps. The connectors use the standard six-pin IEEE 1394 cable. Drivers for the current version of Windows NT are included.

The Bus Stops Here

USB and IEEE 1394 make Windows computing a lot less confusing. They'll add little or nothing to the cost of new PCs and can even breathe new life into older systems. Catch one of these buses-or both-and you'll find yourself cruising down Easy Street.

Lenny Bailes is a San Francisco-based instructor and consultant. Contact him care of the editor at the addresses here.

Windows Magazine, May 1997, page 224.

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