Low End Mac's Online Tech Journal

Introduction to FireWire

Dan Knight - April 1998

By now you've probably heard of FireWire, the new high speed standard for moving data between devices.

Also known as IEEE Standard 1394 or P1394, FireWire was invented by Apple as a faster alternative to SCSI in its many permutations. The typical Ultra SCSI interface runs at 10 MBps (megabytes per second, note capital B), while Wide Ultra SCSI offers double that speed. SCSI-3 goes further, but peaks at 40 MBps. At such high data rates, especially with parallel data connections, cables must be of the highest quality.

Faster than SCSI

FireWire is a serial protocol initially supporting speeds of 100, 200, and 400Mbps (megabits per second, note lowercase b) or 12.5, 25, and 50 MBps. The slowest is two-and-a-half times faster than the typical 8-bit SCSI connection; the fastest is 25% faster than a 16-bit SCSI-3 connection.

But that's not all. The FireWire standard is designed for upward expansion to 800Mbps, 1600Mbps, and beyond. Compare this with the emerging SCSI-4 standard which can reach 80 MBps (640Mbps), but only with the highest quality cables.

Already in use

First adopted for use in digital camcorders, FireWire has found a home in digital audio and video. The same FireWire connection used on consumer products allows them to be attached to any FireWire equipped computer.

Apple has built support for FireWire for PCI-based Macs into every version of the Mac OS since 7.6. All you need is a PCI FireWire card and you're ready to start.

Features

As Apple has implemented it, SCSI supports eight devices. For most of us, that's plenty. But FireWire goes well beyond that, allowing chains of up to 64 devices.

Unless you are willing to damage your computer or SCSI devices, you should only connect or disconnect them when they are all turned off. FireWire is designed for hot connections - no need to turn any device when you add it to or remove it from the chain.

FireWire also says good-bye to those bulky SCSI cables. FireWire cables are like wide 6-conductor phone cables, complete with an easy to use plug on each end. And devices need not be in a single chain; the standard supports branches. And instead of SCSI's 18' maximum chain length, FireWire allows up to 4.5m (15') between devices.

Not only is connection easy, but FireWire is even more plug-play than SCSI. Each device has an ID which the Macintosh FireWire driver can read. Based on this, it knows how to access the device. (BTW, Microsoft is also enamored of FireWire - I'm sure the plug-n-play architecture is a big part of the reason.)

Another nice feature of FireWire is that it can supply up to 60 watts of power to devices. This could eliminate a lot of power bricks and wall plugs.

Beyond Networking

The Macintosh world migrated from 230.4Kbps LocalTalk to 10Base-T ethernet and has been moving toward 100Base-T ethernet, especially for graphics and video, where the older 10Mbps protocol is simply too slow.

Imagine networking a dozen computers, a couple scanners, several huge hard drives, and a whole bunch of digital AV equipment without installing a hub, a server, or special device sharing software.

That's the promise of FireWire.

FireWire allows multiple computers on the same chain, each with access to any device on that chain.

Why invest in an AppleShare server when FireWire lets you share a hard drive at 100-400Mbps? Instead of sending files to the server so it can write them to a central hard drive, you'll be able to write directly to the drive.

Or scan from a central scanner without using a host computer.

Or get digital video directly from a digital camcorder or DVD drive.

The possibilities are endless.

How about a FireWire cable modem? FireWire laser and inkjet printers?

Conventional ethernet networks would be relegated as backbones between FireWire workgroup clusters, since anything within 15' can be directly connected to the chain.

For those of us living with pre-PCI Macs, FireWire is as good a reason to plan on buying a newer Mac as is the increased performance.

Other Resources

• Is FireWire ready for prime time?, MacCentral
• Termination Explained, MOTJ
• USB compared with other ports, Mac Speed Zone
• FireWire: connection of the (near) future, MacTimes
• FireWire Heats Up the Digital World, Apple
• FireWire Home Page
• New Mac Buses on the Horizon, Macworld
• IEEE 1394: A Ubiquitoous Bus , excellent overview
• Apple TIL, About FireWire 400 Technology , quite technical
• Rallying Around the IEEE 1394, a comparison with other interfaces
• FireWire by Shad Stafford
• SCSI