Abstract: In response to the mounting of a magnetic tape on the tape drive, the tape drive begins reading data from the tape into the preload buffer while concurrently signalling the data processor that the tape drive is instantaneously available to read/write data. The data processor can then begin the data transfer operation without incurring the delay occasion by media set up time. The data that is transferred from magnetic tape is stored in the preload buffer in anticipation of the data processor issuing a data read command. Upon receipt of the data read command, the tape drive reads the data out of the preload buffer to the data processor via the data channel while simultaneously reading data from the magnetic tape into the preload buffer.

Abstract: The present invention discloses a method and apparatus for computing CRC codes for fixed length page buffers of user data where the user data arrives from a transmission device in variable length packets with the packet contents being out of sequential order. The received data is written to a storage device after being restored to the correct sequential order. The data packets are comprised of a header portion and a data portion. The transmission and compression methods commonly employed by the transmission device dictates that the header portion of each packet follows the data portion. The present invention computes a complete CRC code for the data stored in a page buffer in real time as the packets are received by using several registers for saving intermediate CRC codes and circuitry to combine partial CRC codes for those packet portions received out of order.

Abstract: Control software and hardware in the tape drive control unit creates and manages a header segment at the beginning of the magnetic tape. This header segment includes an administrative information section that contains data relating to the magnetic tape itself. The administrative information includes read/write status information such as the write protect status of the magnetic tape that enables the tape drive control unit to manage the data records written onto the magnetic tape without reference to any other source of administrative data. In addition, each data record written on the magnetic tape includes a header which denotes the read/write status of the data record.

Abstract: The control software and hardware in the tape drive control unit creates and manages a header segment at the beginning of the magnetic tape. This header is interposed between a leader portion of the magnetic tape on the 3480-type cartridge and the remainder of the magnetic tape contained therein. This header segment contains two sections, a first of which is a data record directory that is used by the control unit to denote the location of each data record written on to the magnetic tape as well as administrative information associated with the data record. The second section of the header is an administrative information section that contains data relating to the magnetic tape itself. The stream of data records is divided into data segments, a plurality of which comprise a single helical scan track. The helical scan tracks are formed into scan groups and written on the magnetic tape.