Browse Prior Art Database

Measuring Tape Movement after Capstan Stop Initiation

IP.com Disclosure Number: IPCOM000090083D
Original Publication Date: 1969-Jan-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 42K

Publishing Venue

IBM

Related People

Breitenbach, RC: AUTHOR

Abstract

Tape movement after initiation of the capstan stop control is measured by the steps of prerecording a particular data pattern on the tape, effecting tape movement commands to initiate stop controls so that the head is within the prerecorded data, performing an erase operation within the prerecorded data block, and reading the residual data in the block.

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Measuring Tape Movement after Capstan Stop Initiation

Tape movement after initiation of the capstan stop control is measured by the steps of prerecording a particular data pattern on the tape, effecting tape movement commands to initiate stop controls so that the head is within the prerecorded data, performing an erase operation within the prerecorded data block, and reading the residual data in the block.

Tape marks TM are defined as recordings of 0's on selected tracks on magnetic tape, with the remainder of the tracks blank, and are typically forty characters long. Also, diagnostic mode means an operation in which recording hardware reacts to any attempt to write consecutive 1's by recording a blank track, instead. This can be selectively performed for any track, any combination of tracks, or all tracks. Although described in terms of a phase encoding system, the arrangement is readily adaptable to other coding methods.

Drawing A shows the process for determining tape movement after capstan stop initiation during a Read Forward command using the diagnostic mode. Beginning burst 10 of forty bytes of 0's,followed by an all 1's byte, is initially recorded and followed by TM 11 and gap 12. The latter is similar to an IBG in character, but is actually only long enough to accommodate read delay and disconnect time. The read delay is a period of time that allows the drive to reach proper speed before the read gates are activated. Gap 12 is followed by another beginning burst 15 and a pattern 16 of alternate data, such as.a 1000 byte sequence of 01, 02, 01, etc. Pattern 16 need only be long enough to ensure positioning of read-write head 20 within the data block when tape movement stops. Ending burst 17 of 0's, followed by a 1's byte, concludes the recorded pattern. After writing this pattern, a Backspace File command is given to cause tape to move to the right past 20 until 20 detects TM 11, at which point 20 is to the left of block 10. A Forward Space Record command is then given which causes tape to move left, past 20, until 20 detects the end of TM 11 to effect initiation of the stop controls. Tape movement during stopping causes 20 to be positioned toward the right until it is in the position shown. After a delay to ensure complete cessation of tape movement, 60 MS, for instance, an Erase Gap command is given which causes the write head W to erase the balance of the recorded patterns right of the head as is shown in the shaded area.

Another Backspace File command again positions 20 left of TM 11. A Forward Space command, followed by a Read command, causes reading of the residual portion of data record 16 between the end of block 15 and the beginning of the erased portion. Since the physical byte-to-byte spacing is known, the residual count can be converted to distance. By adding the known distances for 12 and 15 to the residual count distance and subtracting the known distance between the R-W heads, the remainder is the read stop...