Features of QIC
The QIC cartridge is distinguished from other types of tape cartridges by the fact that it contains an endless drive belt which is moved at a uniform speed by a motorised capstan. Since the belt is in contact with the tape, this ensures both that the tape moves at uniform speed, and that neutral tension is maintained at all times. This is in contrast to cassette tapes or DATs where the tape is moved past the head by a capstan and pinch wheel, but the takeup reel is driven by a servo motor or slipping clutch.
The tape in a QIC cartridge is not physically attached to the reels and is never completely unwound. This is again different from other cassettes or cartridges, which generally have some form of clip anchoring on at least one end of the tape. To ensure that the tape is never completely unwound, each end has a small beginning or end of tape hole which is detected by an optical sensor, and an "early warning" hole further from each end. If a defective drive—for example with fluff in a sensor—winds the tape past the BOT or EOT marker, the tape will detach from the spool and the cartridge will be unusable unless it is reattached.
The design of the QIC tape cartridge is very robust: the aluminium baseplate is an eighth of an inch thick, and the robust plastic cover can withstand abuse and impacts that would damage other tape formats.
However, because the tape is belt-driven, seeking back and forth can eventually cause the tape to become unevenly tensioned. It is therefore necessary to periodically retension the cartridge. This is accomplished by winding the tape from beginning to end and back in one operation, allowing the belt to equalize itself. For newer QIC drives that use a SCSI interface, there is a SCSI "RETENSION" command to do this.
When the cartridge gets old, the belt may not provide enough friction to turn the takeup spool smoothly. When this happens, the tape will need to be replaced.
In some cases a cartridge must be formatted before use. The capability to do this is in the drive rather than the host computer.
Read more about this topic: Quarter-inch Cartridge
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