VXA Autoloader Technology                                                                                                         August, 2004 Page 6 of 8                                                                                              Rather than reading and writing data in a continuous track, which is the technique utilized by older tape technologies such as DDS, DLT and AIT, Exabyte’s VXA Packet Drive reads and writes small, individually addressed packets, similar to the method used to transmit data over the Internet.  Tape drives that read and write in a constant stream require very tight mechanical tolerances to maintain perfect alignment of the tape with the read-write heads. When reading the tape, four tape heads simultaneously read each packet, each slightly offset from the other.  By overscanning with four heads, tape alignment and distortion errors are eliminated.  Should an error be detected, the drive applies a four-level Reed-Solomon Error Correction Code (ECC) that corrects errors in most circumstances, allowing the drive to achieve a bit-error rate of 10^-13.  The combination of overscanning and four-level ECC correction makes the VXA Packet Drive 100 times more likely to recover damaged data than other tape technologies. As each packet is written, a trailing head re-reads the packet to detect write errors.  Upon detecting a write error, the drive re- writes the packet without stopping or rewinding.  Because the packets are individually numbered, they are automatically rearranged into the correct order.  Further, Packet Drive technology allows the drive to adjust the tape speed to match the host data transfer rate, thus eliminating the need to rewind the tape and restart recording.  Hence, Packet Drive technology minimizes job delays and excessive wear on the media and drive mechanism⁶. Because the VXA Packet Drive reads and writes individual packets rather than a continuous stream, the manufacturing tolerances are 270 times larger than competing tape technologies.  This larger tolerance directly translates to a lower cost of manufacture, whereby pricing the VXA Packet Drive at about one-third the cost of comparable tape technologies. Most autoloaders targeted at small to medium-sized businesses are based on a magazine mechanism that selects from a stack of tapes, which the magazine contains.  Exabyte’s VXA-2 PacketLoader is based on a far simpler carousel mechanism that stores tapes in a circle on a platter.  Where the magazine mechanism loading apparatus must precisely move the magazine up or down from one tape to another, the carousel mechanism merely rotates a platter to position the selected tape in front of the drive, eliminating most moving parts.  This streamlined robotics and creative engineering again reduces the cost of manufacture while increasing the device’s reliability. The Exabyte carousel accommodates more tapes than a similarly sized magazine mechanism – ten versus eight or fewer.   With the capacity for ten tapes, the VXA-2 PacketLoader                                                  6 Exabyte Corporation, VXA: Re-Inventing Tape Storage, April 2002 p1   p2   p3   p4   p5   p6   p7   p8