With both PC and Mac platforms switching over to USB as a standard interfacing protocol, the original serial and SCSI connections seem slowly to be being abandoned, notably on the 'boiled sweet look' iMacs, iBooks, G3s and G4s. This leaves many of us with 'legacy' (polite term for obsolete) equipment which we can't plug in. While SCSI PCI cards are an option for G3s and G4s, iMacs and iBooks have no such slots, which means an alternative is needed.
Adaptec have come up with a neat solution to the SCSI problem in the form of USBXchange, a USB‑to‑SCSI adaptor. While USB is considerably slower than modern SCSI connections, it does at least mean you might not have to throw away all your old SCSI peripherals. In practice the Adaptec USBXchange would be fine for use with things like scanners or CD‑R drives (of up to 4x speed), but connected hard drives will only really be useful for backup rather than for multitrack recording or playback.
The USBXchange converts from a USB connection to a mini SCSI 2 connection. The USB end ought to be connected either directly to the computer or to a powered hub, as the unit's power is supplied by the USB interface or by the SCSI peripheral itself. The support software comes on CD‑ROM and installed very easily on my Mac. It added another item to the Control Panel in order to be able to switch between mass‑storage devices and other peripherals — it's important to switch to the correct mode for the SCSI peripheral you're using. You can connect to only one SCSI device at a time, but because the connection to the computer is via USB, hot plugging and unplugging at the USB end is OK. Following the software installation, I booted up Adaptec's Toast and my old Yamaha SCSI CD‑R drive was brought on‑line straight away. I then had no problems burning a backup at 4x speed.
Though the USBXchange is fairly slow by SCSI standards, it does provide a cost‑effective means of connecting SCSI peripherals to USB interfaces. Indeed, in the case of iMacs and iBooks, an adaptor such as this may be the only practical option. Paul White