Abstract: An input and output system has a plurality of tape drives (1-3) connected by a daisy-chained bus (5) to a processor (4). Each of two tape drives (2, 3) at the end of the bus has a terminator (30, 31) for transmit lines (6) of the bus. Each terminator of each line comprises a pull-down resistor (40) connecting the line to ground, and a pull-up resistor (41) and a diode (42) in series connecting the line to a source of potential (43). When a source is powered up, potential is present and a diode connected thereto is forward biased and supplies potential to the line. When the source is powered down and potential is withdrawn, a diode connected thereto becomes reverse-biased and prevents the powered-down source from grounding the line. Redundant termination of each line therefore allows any one tape drive to be powered down without precluding communications over the bus from continuing while the other terminator continues to supply the line with potential.

Abstract: Disclosed is a tape controller (105) that recovers data from a block (203b) of data stored on magnetic tape (109) that has been affected in part by uncorrectable errors such as tape blemishes (213). Upon receiving a request for the block of data, the controller causes a tape drive (108) to read the block from the tape. The controller stores the read data in a buffer memory (111) that is at least the size of the data block. When the tape drive encounters the affected data while reading the block of data, the controller clears the buffer memory and causes the drive to read the block in reverse. The controller again stores the read data in the buffer memory, in the order in which they are read. When the drive again encounters the affected data, the controller reverses the contents of the buffer memory and then causes the drive to read the block in forward. The controller once more stores the read data in the buffer memory, thereby concatenating the two data portions.