Method for testing components of a magnetic storage system

• US 4,796,109 A
• Filed: 03/28/1988
• Issued: 01/03/1989
• Est. Priority Date: 06/05/1984
• Status: Expired due to Fees

• Current Assignee: Unisys Corporation
• Original Assignee: Unisys Corporation
• Inventors: Rose, Andrew M., Sordello, Frank J.
• Primary Examiner(s): Canney, Vincent P.
• Application Number:
  US07/180,659
• Time in Patent Office: 281 Days
• Field of Search: 360/45, 360/31
• US Class Current: 360/45
• CPC Class Codes: G11B 20/10527 Audio or video recording; Data buffering arrangements G11B20/12 - G11B20/18 take precedence
• CPC Class Codes: G11B 20/182 using test patterns
• CPC Class Codes: G11B 5/00 Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor G11B11/00 and G11B13/00 take precedence
• CPC Class Codes: G11B 5/455 Arrangements for functional testing of heads; Measuring arrangements for heads

Abstract

A method for measuring bit shift and other characteristics indicative of the performance of a magnetic storage system, particularly for a system employing a thin-film magnetic head. In a preferred embodiment, complementary patterns are written many times around a circular track of a magnetic disk, each pattern including relatively closely spaced magnetic transitions as well as relatively widely spaced magnetic transitions. The relatively widely spaced transitions are chosen so as to be substantially unaffected by any other transitions. Measurements are made with reference to these widely spaced transitions and averaged for the many patterns recorded in the track so as to rapidly provide highly reliable measurements indicative of system performance.

Claims

1. A method of testing a magnetic storage system comprising the steps of:

providing a recording medium having a relatively large plurality of like recording patterns provided along a track of said medium, each pattern including at least first, second and third magnetically detectable manifestations formed in said medium, said magnetically detectable manifestations being spaced so that the spacings between said first and second manifestations and between said first and third manifestations are relatively large as compared to the spacing between said second and third manifestations, the spacing between said first and second manifestations constituting a first spacing and the spacing between said first and third manifestations constituting a second spacing;

moving said medium and a head relative to one another such that said head traverses said manifestations and produces head output signals in response thereto, said moving also being such that said first manifestation is traversed by said head before said second and third manifestations;

detecting said head output signals produced by said head as said head and medium are relatively moved;

producing in response to said detecting an indication of bit shift based on the difference between the time interval detected in response to said head traversing the manifestations corresponding to at least one of said first and second spacings and a reference time interval corresponding to that which would be obtained if there were no bit shift, and wherein said producing step produces said indication taking into account the differences obtained between its respective detected and reference time intervals for a relatively large plurality of said like recording patterns recorded in said track.

2. The invention in accordance with claim 1, wherein the step of producing includes producing in response to said detecting an indication of left bit shift based on the difference between the time interval detected corresponding to said first spacing and the time interval that would be obtained if there were no bit shift, and also producing in response to said detecting an indication of right bit shift based on the difference between the time interval detected corresponding to said second spacing and the time interval that would be obtained if there were no bit shift.

3. The invention in accordance with claim 1 or 2, wherein said first manifestation is sufficiently spaced from said second and third manifestations so as to have substantially no effect on the detected locations thereof.

4. The invention in accordance with claim 3, wherein the spacing between said second and third manifestations corresponds to the closest spacing required to be detected by said head.

5. The invention in accordance with claim 1, wherein said producing step produces said indication based on the average of the differences obtained between its respective detected and reference time intervals for a relatively large plurality of the patterns recorded on said track.

6. The invention in accordance with claim 5, wherein said first manifestation is sufficiently spaced from said second and third manifestations so as to have substantially no effect on the detected locations thereof.

7. The invention in accordance with claim 1, wherein a relatively large plurality of second patterns are additionally provided in said track interspersed with the first-mentioned patterns, wherein each manifestation of said first-mentioned and second patterns comprises a magnetic transition having either a positive-going or a negative-going direction, wherein adjacent ones of said transitions are oppositely directed, and wherein transitions in said second pattern have substantially the same relative locations as those in said first-mentioned pattern but being oppositely directed thereto.

8. The invention in accordance with claim 7, wherein said method includes producing an indication of timing asymmetry based on the jitter detected for particular corresponding intervals of said first-mentioned and second patterns.

9. The invention in accordance with claim 7, wherein said method includes producing an indication of timing asymmetry based on the jitter detected for corresponding intervals of said first-mentioned and second patterns having oppositely directed beginning and ending transitions.

10. The invention in accordance with claim 7, wherein said method includes producing an indication of timing asymmetry based on the resulting comparative jitter obtained when the jitter detected for corresponding intervals of said first-mentioned and second patterns formed by oppositely-directed beginning and ending transitions is compared to the jitter detected for corresponding intervals of said first-mentioned and second patterns formed by like-directed beginning and ending transitions.

11. The invention in accordance with claim 10, wherein said indication of timing asymmetry is based on the standard derivation of said comparative jitter.

12. The invention in accordance with claim 8 or 9, wherein said corresponding intervals comprise the intervals between the respective first and second transitions of said patterns.

13. The invention in accordance with claim 10 or 11, wherein said corresponding intervals of said patterns formed by oppositely-directed beginning and ending transitions comprise the intervals between the respective first and second transitions of said patterns, and wherein said corresponding intervals of said patterns formed by like-directed beginning and ending transitions comprise the intervals between the respective first and third transitions of at least one of said patterns.

14. The invention in accordance with claim 1, wherein the step of providing includes providing calibration signals corresponding to those used for recording said pattern on said medium, converting said calibration signals into idealized head output signals, and then using these idealized head output signals for said detecting so as to provide a calibration value for each indication.