USB: Ready for Prime Time?
Perhaps the biggest variable in the iMac’s equation is Apple’s renunciation of its old connectivity standbys—SCSI, ADB, and traditional Macintosh serial ports—in favor of the Universal Serial Bus (USB).
The bad news is that no current Mac peripherals support USB. Unless printer, scanner, or other external-device manufacturers take the time to write special drivers and provide adapter cables, chances are that iMac owners won’t be able to use any devices they already own—or those released before the iMac’s debut. It’s physically possible to connect non-USB peripherals to the iMac with an adapter, but peripherals vendors must write USB drivers before their devices can communicate with the iMac.
Apple claims that hardware vendors will offer a wide variety of USB devices for the iMac, although the company was unwilling to reveal names at press time. Surprisingly, Apple itself has no plans to offer critical devices such as floppy and Zip drives and instead will rely on third parties.
Although USB offers an inexpensive and speedy alternative to traditional serial and ADB, it’s a poor substitute for SCSI because the speeds of USB devices are interdependent: the more active devices on the bus, the slower each USB peripheral is likely to perform—a major issue for storage products.
But the good news is that a machine equipped with USB can support up to 127 logical devices, including disk drives, keyboards, mice, modems, scanners, cameras, printers, and even monitors. Still, the iMac’s two ports might seem rather skimpy, considering that every peripheral device has to have its own connection. However, because USB uses a hub topology (like Ethernet), adding more ports is simply a matter of connecting a powered USB hub, a feature built into many USB devices. The keyboard that comes with the iMac acts as such a hub: both the mouse and another USB device can be plugged into it.