# US 5,353,170 A · Error recovery data storage system and method with two position read verification > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,353,170 A - Document ID: US5353170A - Status: Granted - Kind: A - Application number: 08/064,297 - Filed: 1993-05-19 - Granted: 1994-10-04 - Earliest claimed: 1993-05-19 - Assignees: International Business Machines Corporation - Inventors: Kwok W. Fung; Robert L. Kwok; Arvind M. Patel; Robert A. Rutledge - Web page: https://patentgrep.com/patent/US5353170A ## CPC - G11B 5/012: Recording on, or reproducing or erasing from, magnetic disks (G11B17/00, G11B19/00 take precedence) - G11B 19/04: Arrangements for preventing, inhibiting, or warning against double recording on the same blank or against other recording or reproducing malfunctions - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A direct access storage device (DASD) system uses a read/write head having a wide transducer write element and a narrow magneto-resistive read element. In order to avoid mistakenly reading a incompletely erased old data field, the system uses a verification procedure. Data are read at two positions along the data track which are separated by a radial distance D. This distance D is selected to be greater than the width of any incompletely erased data record. If the data read at the two read positions are equal, then the data are deemed to be correct and are sent to a host system. ## Claims ### Claim 1 A data storage system comprising: a data storage medium having data tracks; a read element; a read means connected to the read element for causing the read element to read data from a data track; a movement means for moving the medium relative to the read element; a positioning means for moving the read element relative to the data storage medium to different positions across the width of the data tracks; and a control means connected to the positioning means for controlling the movement of the read element such that two successful reads are made a distance D apart on the same track, the control means further including a comparison means for comparing the data read from the two reads to determine if they are the same. ### Claim 2 (depends on 1) The system of claim 1, wherein W/4.ltoreq.D.ltoreq.W2, where W is the width of the data track. ### Claim 3 (depends on 1) The system of claim 1, wherein D is substantially equal to W/3, where W is the width of the data track. ### Claim 4 (depends on 1) The system of claim 1, wherein the data storage medium has a magnetic recording layer. ### Claim 5 (depends on 1) The system of claim 1, wherein the read element is a magneto-resistive element. ### Claim 6 (depends on 1) The system of claim 1, wherein the comparison means compares a selected portion of the data from the two successful reads. ### Claim 7 (depends on 1) The system of claim 1, wherein the comparison means compares the cyclical redundancy check code of the two successful reads. ### Claim 8 (depends on 1) The system of claim 1, further comprising a write element connected to the positioning means and having a width greater than the width of the read element. ### Claim 9 (depends on 1) The system of claim 1, wherein the distance D varies according to the length of the data to be read. ### Claim 10 (depends on 1) The system of claim 1, wherein the control means causes the read element to be moved in incremental distance away from an initial position in order to obtain a first successful read. ### Claim 11 (depends on 10) The system of claim 10, wherein the distance D varies according to the number of incremental distances which the head element has been moved. ### Claim 12 A method for a data storage system comprising the steps of: moving a read head to a first position along the width of a data track of a data storage medium; reading the data track at the first position; determining if a successful data read has occurred at the first position; storing the information read at the first position; moving the read head to a second position along the width of the data track, the second position being a distance D from the first position; reading the data track at the second position; determining if a successful data read has occurred at the second position; and determining if the data of the first read are equal to the data of the second read and transmitting the data if they are equal. ### Claim 13 (depends on 12) The system of claim 12, wherein W/4.ltoreq.D.ltoreq.W/2, where W is the width of the data track. ### Claim 14 (depends on 12) The system of claim 12, wherein D is substantially equal to W/3, where W is the width of the data track. ### Claim 15 (depends on 12) The system of claim 12, wherein the data storage medium has a magnetic recording layer. ### Claim 16 (depends on 12) The system of claim 12, wherein the read head is a magneto-resistive element. ### Claim 17 (depends on 12) The system of claim 12, wherein the step of determining if the data are equal is comprised of comparing a selected portion of the data from the two successful reads. ### Claim 18 (depends on 12) The system of claim 12, wherein the step of determining if the data are equal is comprised of comparing the cyclical redundancy check code of the two reads. ### Claim 19 (depends on 12) The system of claim 12, wherein the read element has a width less than the width of a data track. ### Claim 20 (depends on 12) The system of claim 12, wherein the distance D varies according to the length of the data to be read. ### Claim 21 (depends on 12) The system of claim 12, further comprising the step of moving the read head in incremental distances away from an initial position in order to obtain a first successful read. ### Claim 22 (depends on 21) The system of claim 21, wherein the distance D varies according to the number of incremental distances which the read had has been moved. ### Claim 23 A data storage system comprising: a data storage medium having data tracks; a read element; a read means connected to the read element for causing the read element to read data from the data track; a movement means for moving the medium relative to the read element; a positioning means for moving the read element relative to the data track to different positions across the width of the data tracks; and a control means connected to the positioning means for causing the read element to be moved in alternating positive and negative incremental distances away from an initial position until a first successful read has been made of the data, and for causing the read element to be moved to a second position a positive distance D away from the position of the first successful read if the first successful read was made at a positive incremental distance and causing the read element to be moved to a second position a negative distance D away from the position of the first successful read if the first successful read was made at a negative incremental distance, such that a second successful read is made at the second position, the control means further including a comparison means for comparing the data read from the first position and the second position to determine if they are the same. ### Claim 24 (depends on 23) The system of claim 23, wherein W/4.ltoreq.D.ltoreq.W/2, where W is the width of the data track. ### Claim 25 (depends on 23) The system of claim 23, wherein D is substantially equal to W/3, wherein W is the width of the data track. ### Claim 26 (depends on 23) The system of claim 23, wherein the data storage medium has a magnetic recording layer. ### Claim 27 (depends on 23) The system of claim 23, wherein the read element is magneto-resistive element. ### Claim 28 (depends on 23) The system of claim 23, wherein the comparison means compares a selected portion of the data read from the first and second positions. ### Claim 29 (depends on 23) The system of claim 23, wherein the comparison means compares the cyclical redundancy check code of the two successful reads. ### Claim 30 (depends on 23) The system of claim 23, wherein the distance D varies according to the length of the data to be read. ### Claim 31 (depends on 23) The system of claim 23, wherein the distance D varies according to the number of incremental distances which the read element has been moved. ### Claim 32 (depends on 23) The system of claim 23, further comprising a write element connected to the positioning means and having a width greater than the width of the read element.