IBM 3590 and 3592 SCSI drives support the "READ REVERSE" SCSI command[1] which (in variable-block transfer mode) is equivalent to the "READ BACKWARD" channel co

IBM 3590 and 3592 SCSI drives support the "READ REVERSE" SCSI command[1] which (in variable-block transfer mode) is equivalent to the "READ BACKWARD" channel command. For application details, see Knuth volume 3 [2], which even has a fold-out chart illustrating tape (and tape operator) movements involved in various sorting algorithms[3]. In brief, reading backwards allows you to use tape as a stack. [1] https://www.ibm.com/support/pages/system/files/inline-files/$FILE/3592%20SCSI%20Reference%20(EXTERNAL)_3.pdf#page=194 https://www.ibm.com/support/pages/system/files/inline-files/... [2] https://archive.org/details/B-001-001-250/page/299/mode/1up https://archive.org/details/B-001-001-250/page/299/mode/1up [3] https://archive.org/details/B-001-001-250/page/n356/mode/1up https://archive.org/details/B-001-001-250/page/n356/mode/1up