64 bytes of user data, a synchronization marker, unique address information, Cyclical Redundancy Check (CRC) code and Error Correction Code (ECC). Each Packet Segment on the VXA tape includes 387 data packets recorded and read through a special buffer segment. The VXA “Perfect Write”  . VXA  Packet Drives are the only production tape drives in the world that employ a zero-tolerance “perfect write”. When writing data, the VXA drive records a pair of alternate azimuth packets during each rotation of the drum. With a zero tolerance write, a second head (the trailing head) reads the data packets that were just recorded to the tape. If the VXA drive detects inaccurate data in a packet, then the affected packet will actually be re-written on-the-fly. This results in a zero tolerance for write errors at the packet level. While other conventional tape drives write some “allowable amount of errors” during their write cycle, VXA allows none. The VXA Packet Technology Read/Restore Cycle. When reading data, the VXA drive does not need to sequentially trace tiny track geometries. Instead, it uses all four heads to completely scan the surface of the tape. This technique allows the VXA drive to read data packets with multiple scans (overscanning), ensuring that each packet is easily read no matter where it is on the tape (see Figure 2). The geometry of packet sections and variation in section pitch are insignificant because every packet will be read, regardless of where it lies on the tape surface. This technique is especially valuable when the tape has been damaged or when reading a tape in one VXA drive that was written by another VXA drive guaranteeing interchange. Buffer Segment. During a read operation, all four heads scan the tape and read the data packets into a buffer segment. Because each packet has a unique address, the VXA buffer reassembles the packets in the correct order, regardless of the order in which they were received. Packets that were read correctly in the first pass are retained in the buffer. Packets that were missing in the first pass are read in subsequent passes and are added until the data strings are complete. Once complete, the data is forwarded to the host. This is a technique similar to that used in the networking, Internet, and rewriteable CD technologies. p1   p2   p3   p4   p5   p6