CA1111553A

CA1111553A - Minor bit reduction on a magnetic head

Info

Publication number: CA1111553A
Application number: CA292,764A
Authority: CA
Inventors: Peter T. Marino; Frank B. Shelledy; Edmond W. Smathers
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1977-03-28
Filing date: 1977-12-09
Publication date: 1981-10-27
Also published as: DE2813193A1; JPS623488B2; JPS6313248B2; US4149204A; JPS53120514A; DE2813193C2; JPS58114320A; IT7821513A0; IT1109182B; FR2386097A1; GB1571175A; FR2386097B1

Abstract

MINOR BIT REDUCTION ON A MAGNETIC HEAD
Abstract A magnetic head assembly for cooperating with a relatively moving medium, on which servo information and data information is recorded, and for reading and/or writing on said medium and for erasing said medium is fabricated so that the effect of pickup interference or unwanted signals during playback is reduced. The magnetic head assembly incorporates a geometry which shifts the signal envelope of the interfering signal so that it is in phase with the signal envelope of the desired signal. The preferred geometry is to dimension the head core so that the distance between two gaps or between a single gap and the edge of the core is equal to the distance between the servo tracks on said media. Additionally, the gap of the head has a gap null occurring at the frequency of the interfering signal.

Description

17 Background Of The Invention 18 1. Field of the Invention 19 The invention relates to an improved magnetic head structure which allows the reading of recorded data, from a 21 magnetic recording media, without picking up spurious signals.
22 More specifically, the invention allows the reading of servo 23 information without suffering servo errors.
24 2. Prior Art The use of magnetic heads for recording and re-26 producing information on a recording media is well known and 27 has become more important in recent years. Although the 28 magnetic recording media may take a plurality of different .

, . . . . ~

llllSS3 1 forms, e.g. disc (flexible and/or solid) tape, etc.,

2 there are only few characteristics which are necessary to

3 identify such medias. Generally, a slurry in which magnetic

4 particles are suspended is uniformly spread over a thin S supporting structure. The structure is then cured to form a 6 recording media. r 7 When a magnetic field, which is created by a 8 magnetic head, etc., is passed relative to the surface of the 9 recording media, the magnetization o~ the magnetic particles are aligned in accordance with the applied magnetic field to 11 store data. In order to recover or reproduce the sto~ed 12 data, a magnetic head is positioned relative to the media 13 and by cutting the magnetic lines the recorded data is 14 reproduced-In order to store and/or retrieve the magnetic 16 data, in an orderly manner, the magnetic media is generally 17 divided into data zones and servo zones. The data zones are 18 the areas in which data is recorded, while the servo zones 19 are the areas in which track following servo information is20 recorded 21 For reproducing the recorded signal the magnetic 22 head is passed relative to the media so as to traverse both 23 data and servo zones. One problem associated with this 24 system is that as the magnetic head traverses the media, 25 spurious readback signals are generated. The spurious 26 readback signals are outputted with the signal envelope 27 which contains the useful data to be recovered. These 2~ spurious signals hereinafter called minor bit, present l~LllS53 1 problems for the detection circuits which process the 2 reproduced signals. In fact, whenever the problem occurs in 3 the servo zone, whole data cartridges are sometimes rejected 4 as being defective when, in fact, these data cartridges are good.
6 The source of the minor bit problem is that in 7 addition to the head gap which does normal reading, the 8 edges of the head core and/or a nonactivated gap in a dual 9 or multiple .gap head also reads and outputs signals. Several approaches have been practiced in the prior art to solve the 11 minor bit problem. For example, in one attempt the prior 12 art uses filters to filter out the unwanted signal from the 13 reproduced signal. Although this method wor~s satisfactorily, 14 it tends to increase system cost since the readback circuits j 15 are more complex than if the filtering function was not 16 necessary. Also, in the situation where the minor bit is 17 mainly associated with the servo zone of the recording 18 media, the filtering circuit has minimal use since the 19 filtering circuit is only operable for the relatively short 20 period of time when the magnetic head is traversing the 21 servo zone.
22 In still another attempt the prior art uses shielding 23 to solve the minor bit problem. However, shielding tends to 24 increase head cost and also the complexity of the head.
25 Also, shielding does not solve the minor bit pro~lem in all 26 cases, for example, when the nonactivated gap of a dual gap 27 head is reading servo data as the head traverses the servo 28 zone.

1~11553 1 Summary Of The Invention 2 The above mentioned prior art problems are solved 3 by fabricating a magnetic transducer with unique geometries.
4 The geometries are such that when the head gap reads servo and/or data information on the media, spurious signals (i.e.
6 minor bit) are suppressed or are shifted from the main 7 signal envelope.
8 In one feature of the invention the magnetic 9 transducer incorporates a single gap position within a lO magnetic core. The gap is characterized by being a high 11 reluctance magnetic path which is formed between an i~ner 12 pole piece and the outer pole piece of the core. A coil 13 accessing window is fabricated within the outer pole piece 14 of the core and a pic~up coil is wound thereon. The core is 15 dimensioned so that the edge of the core and the gap taken 16 in the direction of head travel are separated by a distance 17 equal to the centerline distance between the servo tracks.
18 In another feature of the invention the magnetic l9 head includes a magnetic core with two gaps fabricated therein. The gaps are so positioned that the spacing between 21 the gaps is equal to the servo pitch spacing.
22 In still another feature of the invention, one of 23 the gap lengths of the dual gap head is such that a null 24 occurs when reading at servo density.
The foregoing and other features and advantages of 26 the invention will be apparent from the following more 27 particular description of preferred embodiments of the .,~
28 invention, as illustrated in the accompanying drawings.

li~l5~3 1 Brief Description of the Drawings 2 FIGURE 1 is an elevational view of a single gap 3 magnetic head which utilizes the geometry of the present 4 invention.
FIGURE 2 shows a section of magnetic media with 6 servo and data tracks thereon.
7 FIGURE 3A shows the resulting signal envelope 8 which is read by the magnetic head according to the present 9 invention and is helpful in understanding the operation of 10 the magnetic head.
11 FIGURE 3B shows a resulting signal envelope,from a 12 magnetic head which does not embody the present invention.
13 FIGU~E 4 shows a dual gap magnetic head in which 14 the geometry and the gap width incorporate the present 15 invention-16 FIGURE 5 is a curve showing the amplltude of a 17 readback signal and its relation with the wave length lambda 18 t~) of said signal.
19 FIGURE 6 depicts a top view of the surface of a 20 single gap magnetic head and the relationship of the gap to 21 the edge of the core.
22 FIGURE 7 is a top view of a dual gap magnetic head 23 showing the critical spacing between the gaps.
24 FIGURE 8 shows the servo envelope which is read ~y 25 the readback head. The servo envelope is used to position 26 the read head relative to a selected track.

llll~S3 1 Description of the Prefered Embodimont 2 of the Invention 3 Although several terminologies and names are used 4 in the literature to define the spurious pulses which are

5 generated by the outside corners of a readback head or the ; 6 spurious signals generated by one of a nonoperational dual 7 gap head; the ter~ "minor bit" is the terminology used in 8 this specification to define the spurious signal. As such, 9 the term minor bit, as is used in this specification, means 10 the spurious readback signal envelope which is generated by 11 the edges of a magnetic core or from one of the gaps ~f a 12 dual gap head.
13 Referring now to the drawings, and more particularly 14 FIGURES 1 and 4 thereof, there is shown a magnetic transducer 15 or head generally designated by the numeral 10 for cooperating 16 with a relatively moving magnetic medium 12 for reading 17 and/or writing a track or tracks of magnetic information 18 thereon.
19 - Magnetic medium 12, a section of which is shown in 20 FIGURE 1, is shown in greater detail in FIGURE 2. Although 21 the magnetic medium 12 is shown as a section of magnetic 22 tape, recorded as in a rotating head device, it is contemplated 23 within the scope of this invention that the magnetic media 24 may take various forms and shapes, for example, a magnetic 25 disk. Magnetic medium 12 includes a data recording section 2~ in which a plurality of data tracks are recorded. Two of 27 these tracks, 16 and 18, are shown in the figure. The data 28 tracks are generally inclined at an angle to the edge of the ~' .

15~;3 1 magnetic medium 12. Positioned from either edge of the 2 magnetic medium 12 and to straddle the data tracks are servo , . ,~
3 tracks 20, 22, 24 and 26 respectively. Positioned in the 4 servo tracks are sync marks which identify the centerline or ~5 the ideal head path for a selected data track. Each of the -;6 servo tracks has a multiplicity of servo indicia which are 7 substantially parallel to the sync marks. A plurality of 8 these servo indicia identified as 28 and 30 respectively are 9 shown in FIGURE 1, where an expanded view of servo track 20 10 and 22 is shown. As will be explained subseqlently, the .!j' 11 servo indicia, together with the sync marks are used by the 12 magnetic transducer 10 for track following. Track following 13 as is used herein means that the magnetic transducer is 14 aligned (i.e. in registry) with a selected data track.
15 Stated another way, track following means the ability of the 16 magnetic transd~cer to align with and to traverse a selected 17 data track to read and/or write magnetic information into 18 said track.
19 Referring again to FIGURES 1 and 4, magnetic 20 transducer 10, which is in accordance with the present 21 invention is shown. The magnetic transducer of FIGURE 1 22 depicts a single gap head while the magnetic transducer of 23 FIGURE 4 is a dual gap head, both of which incorporate the 24 present invention.
The single gap head of FIGURE 1 includes an inner 26 pole piece 32. A coil window is fabricated in an outer pole 27 piece 34 and is then attached to inner pole piece 32 to form 28 a conventional transducing gap 36~ Gap 36 is characterized 1111~53 1 by its high reluctance. In order to establish gap 36 con-2 ventional head manufacturing techniques are used. For 3 e~ample, the gap may be an open space which is positioned 4 between inner pole piece 32 and outer pole piece 34, or the gap can be filled with nonmagnetic material; example, glass.

6 A winding 38 is seated on outer pole piece 34 through the

7 window in said pole piece. External circuits for reading

8 and writing are connected to terminals ~2 and 40 respectively.

9 In order to achieve the results of the present invention, the effective spacing between gap 36 and the leading edge of 11 outer pole piece 34 is equal to 'A' where 'A' is equa~ to 12 the effective spacing between the centerlines of the servo 13 tracks at the angle at which the head crosses the servo 14 tracks.
In order for magnetic transducer 10 to read data 16 recorded in the servo tracks, the head enters the track at 17 an angle (e) and travels in a direction identified by arrow 18 44. Assume that the normal spacing between the centerline 19 of the servo tracks is identified by 'B'. It can be seen from the geometry of FIGURE 1 that the effective spacing 'B' 21 between servo tracks 20 and 22, which is also the required 22 spacing 'A' between the gap 36 and leading edge of transducer 23 10 is equal to B '. cos e. FIGURE 6 shows a plain view of 24 the transducer surface which interfaces the magnetic media.
25 Gap 36 is formed at the junction of inner pole piece 32 and 26 outer pole piece 34 while dimension 'A' is substantially 27 equivalent to the spacing between the servo tracks at the 28 angle at which the head crosses the servo tracks.

lillS53 1 Before describing the construction of the dual gap 2 head it is worthwhile discussing the problems which are 3 experienced when a head is used which does not conform to 4 the teaching of the present invention. As was stated previously, in order to read or write information from a selected track 6 on the media, magnetic head 10 accesses the media at an 7 angle theta (e) in ~he direction shown by arrow 44 to read 8 and/or write information from the media. Track following or g head media position information is derived from ~he pre-recorded information which is maintained in the servo tracks.
11 FIGURE 8 shows the output signal envelope from the ma~netic 12 head 36. The output signal envelope is substantially 13 diamond shaped, however, after rectification only one-14 half of the diamond is shown. In order to define track alignment a threshold level shown at points 46 and 48 on the 16 leading and trailing slope of the servo output signal are 17 chosen. Whenever the reading circuits, not shown, are 18 connected to terminal 40 and 42 of winding 38 (FIGURE 1), 19 encounters point 46, which is on the leading slope of the servo signal the circuit begins to count up. On reaching 21 the peak of the signal envelope at point 50, a double frequency 22 bit which is supplied by the sync mark is encountered. On 23 encountering this bit, the circuit begins to count downward.
24 Counting downward continues until point 48 is reached. If 25 the head is on track then the contents of the counting 26 circuit is zero. Alternately, if the head is not on track 27 then there is a remainder in the counting circuit and the 28 system is so informed and a servo error is issued. A more g _ J ~llS.~3 1 detailed discussion of this posi,ioning scheme may be found 2 in U.S. Patent 3,845,500 issued to Gary Hart and assigned to 3 the assignee of the present invention. Although the point 4 50 of the servo signal is shown with a peak (i.e., pointed), in some designs the peak is flat. This type o~ track following 6 is called amplitude track following since the alignment of 7 the head with a selected track is dependent on the amplitude 8 of the signal.
9 Referring now to FIGURE 3B, a signal envelope which is derived from a magnetic head which is not designed 11 in accordance with the teaching of the present inven~ion is 12 shown. This diagram is also helpful in understanding the 13 problem which is caused by the minor bit. As the leading 14 edge of the transducer 10 reads across the servo tracks, the edge reads the recorded information in the servo track and 16 outputs spurious signal envelope identified as the minor bit 17 envelope. As can be seen from the sketch, these minor bit 18 envelopes overlap the main envelope which is derived from 19 the gap of the transducer. Also, the peak 52 of these minor bit envelopes is positioned on the slope of the main envelope.
21 When a composite signal is derived from the minor bit envelope 22 and the main envelope, an irregular shape waveform is created.
23 The discontinuity which occurs in the composite envelope, 24 as a result of the peak of the spurious signal envelope, 2~ and the main envelope is due to a 180 phase change occurring 26 with the sync pulse. For example, in FIGURE 3B the irregularity 27 or discontinuity occurs on the leading slope, and at the 28 peak of the main envelope. As was stated previously, the 1 system is dependent on the amplitude of the servo signal for 2 track following. By positioning the threshold to coincide 3 with the irreg~lar leading slope of the main servo envelope, 4 the counting circuit issues a plurality of servo errors 5 which affects system throughput when, in fact there is no 6 error.
7 Turning to FIGURE 3A for awhile, the servo signal 8 which is outputted from a head design according to the 9 present invention is shown. As is evident from the figure,

10 the minor bit envelope is so transformed that the peak 52 is

11 either in phase with the peak S0 of the main envelope,or out

12 of phase with the peak of the main envelope. When magnetic

13 transducer 10 is designed so that the peak does not coincide

14 with the slope of the main servo envelope, a composite servo

15 envelope is generated which does not have irregular shape.

16 By positioning a threshold along the leading slope and the

17 trailing slope of the composite signal, the servo error is

18 significantly reduced and data throughput is increased. In

19 order to achieve the result which is sho~Jn in ~IGURE 3A, the

20 transducer of FIGURE 1 has a dimension substantially equivalent

21 to the effective distance between servo tracks.

22 Referring now to FIGURE 4, an alternative embodiment

23 of the invention is shown. In this embodiment of the in-

24 vention, magnetic head 10 includes dual gaps 54 and 56

25 respectively. Gap 54 is a so-called write/read gap while

26 gap 56 is a so_called erase gap. It should be noted that

27 the function of these gaps may be changed without departing 2~ from the scope of this invention. The charcteristic on the second embodiment is that magnetic head 10 has two gaps 1 which are positioned relatively close to each other.
2 Although it is within the skill of the art to use conventional 3 magnetic head technology for fabricating magnetic head 10, 4 in the preferred embodiment of the invention magnetic head 10 includes a center pole piece 58. Attached to the center 6 pole piece 58 is first outer pole piece 60 hereinafter 7 called first support relief 60. First support relief 60 is 8 fabricated with a window section which enables write winding 9 62 to be seated thereon. Write wir.ding 62 is connected to terminals 64 and 66 respectively; this allows write current 11 to enter the winding and data information to be subtr~cted - 12 from the winding. Position between pole tips 68 and 70 is 13 write/read gap 54. Gap 54 is characterized by having a 14 relatively high reluctance. The gap is fabricated by 15 conventional means; it may be a mere air gap or the gap may 16 be filled with nonmagnetic material, for example, glass.
17 Likewise, erase gap 56 is formed by positioning pole 72 18 relative to pole 70. As with first support relief 60, 19 second support relief 74 is fabricated with a window upon 20 which erase winding 76 is seated. Windiny 76 is connected 21 to terminals 7~ and 80 respectively and functions to transmit 22 current to and from the erase gap 56. As with the ~ingle 23 gap head, the spacing 'C' between the centerline of the gaps 24 is equal to the effective distance between servo tracks at 25 the angle of traverse e. By designing the dual gap head so 26 tha~ the spacing is equivalent to the effective spacing 27 between the servo tracks, the envelope of the minor bit

28 signal which is picked up by the erase head during the time llli~3 1 period when the write/read head is reading across the servo 2 tracks to obtain trac]c following inforMation is in phase 3 with the main envelope. Although the gaps 54 and 56 respec-4 tively have been identified as a write/read gap and erase gap, this should not be regarded as a limitation on the 6 scope of the invention since it is within the skill of the 7 art to alter the assignment without departing from the scope 8 of the invention. It is, therefore, ncted that one of the 9 important features in the dual gap head is that the distance 'C' must be equivalent to the effective centerline spacing 11 between servo tracks at the angle of traverse.
12 FIGURE 7 shows a flat view of the surface of the 13 magnetic head which interfaces with the magnetic media. As 14 is evident from this diagram, the distance 'C' is the distance between the centerline of the erase gap and the read/write 16 gap. This distance is substantially equivalent to the 17 effective distance between the servo tracks at the angle of 1~ traverse 19 Still referring to FIGURE 4 and FIGURE 7, yet 20 another embodiment of the present invention is sho~n. In 21 this embodiment of the invention the width 82 of the erase 22 gap 56 is fabricated so that as the magnetic head traverses 23 the servo zone, of the media, minor bit which is picked up 24 by the erase gap is suppressed. This is achieved by making 25 the width of the erase gap so that a null in the gap loss 26 function occurs at the linear density of the servo tracks.
27 It should be noted that this principle is applicable for 28 suppressing one of a plurality of signals recorded at different 11115~3 1 frequencies or densities. This is done by designing one of 2 the head's gaps to have a null at the frequency of the 3 unwanted signal. Referring to FIG~RE 5 for awhile, a graph 4 showing the relationship between the amplitude of the playbac~
s signal which is outputted from the read head and its relation-6 ship with the wavelength (lambda ~) of the recorded signal 7 is shown. This graph is helpful in understanding the underlying 8 theory upon which the erase gap is fabricated. As can be g seen from the figure, when the null of the recorded signal is present, the output amplitude in the playback head is 11 zero. Therefore, by designing the head gap whose rea~ding is 12 not required to read at the null of the recorded signal, the 13 minor bit problem is reduced. In fact, the minor bit is 14 eliminated It is known in the recording technology that:
16 1.12 17 where A = 2 ; D is linear density in flux changes per 18 unit length.

By substituting the value for ~ in equation 1, it is determined that;
Gap Width = 1 x 2 ; (Equation 2) 22 1.12 D
23 By substituting the density at which a specific signal is 24 recorded in equation 2, then a gap width can be designed 25 which will not read bac~ a specified signal when the gap is 26 traversing recording media upon which the data is recorded.
In the preferred embodiment of this invention, the servo 28 data which is to be suppressed has a density of 3440 flux changes per inch, therefore, a gap width of approximately 1 581 microinches allows the head to read across the servo 2 sector without outputting minor bit from the erase gap.
3 In the above description of the dual gap head 4 (FIGURE 4) it is assumed that for normal operation the direction of head travel relative to the magnetic media (not 6 shown) is depicted by arrow 81. Stated another way, in 7 normal operation the erase gap precedes the write/read gap.
8 This means that the erase gap accesses or encounters recorded 9 data and/or recorded servo information prior to the write/read gap. When the dual gap head is operated in the aforementioned 11 mode, if the width of the erase gap is such that a nu~l in 12 the gap loss function occurs at the linear density of the 13 servo tracks; then the erase gap contribution to the "minor 14 bit" phenomenon is suppressed. Therefore, the distance 'C' (FIGURES 4 and 7) does not have to be equivalent to the 16 effective distance between the servo tracks at the angle of 17 traverse. However, if the erase gap cannot be fabricated so 18 that a null in the gap loss function occurs at the linear 19 density of the servo tracks or if the direction of operation is reversed (i.e. the write/read gap accesses data and/or 21 servo information prior to the erase gap) then in order to 22 suppress or control the "minor bit" the distance 'C' must 23 be substantiall~ equivalent to the effective distance between 24 the servo tracks at the angle of traverse.
Likewise, the corner of the head nearest to the 26 write/read gap of the dual gap head contributes a minor bit 27 if the head is operated (i.e. access data and~or servo 2~ information) in the aforementioned reversed mode. To solve l~li5~3 1 this "minor bit" problem, the distance 'D' (FIGURE 4) must 2 be substantially equivalent to the ef~ective distance bet~een 3 the servo tracks at the angle of traverse. For optimum 4 control of the "minor bit" phenomenum and to allow reversibility of head operation, distances 'C' and 'Dr (FIGVRE 4) must be 6 substantially e~uivalent to the effective distance between 7 the servo tracks at the angle of traverse; while the width 8 of the erase gap is such that a null in the gap loss function 9 occurs at the linear density of the servo tracks. All of the three aforementioned characteristics (i.e. the control 11 length of distance 'C' and distance 'D' and the widt~ of the 12 erase gap) must be designed concurrently into the dual gap 13 head for optimum control.
14 By fabricating a magnetic transducer in accordance 15 with the above described invention, data is reproduced from 16 a magnetic recording surface without minor bit interference.
17 Although the invention is described in a rotatory head en-18 vironment wherein head/track alignment is maintained from 19 the contents of servo tracks positioned on both edges of a 20 length of magnetic media, this teaching is only explanatory 21 rather than a limitation on the scope of this invention;
22 it is contemplated within the scope of the invention that 23 the described teaching, specifically the magnetic head as is 24 claimed, is applicable in any magnetic recording environment 25 in which the servo track is used for positioning the head 26 relative to a data track, for example, in a disk environment.
27 Also, this head can be used to suppress one of a plurality 28 of signals recorded at different frequencies on a magnetic

29 recording surface.

llllSS3 1 While the invention has been particularly shown 2 and described with reference to the preferred embodiment 3 thereof, it will be understood by those skilled in the art 4 that various changes in form and details may be made therein 5 without departing from the spirit and scope of the invention.

1 1 !

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A magnetic head assembly, for use with a relatively moving magnetic medium having longitudinal servo tracks and data tracks inclined to said servo tracks, said magnetic head moving traversely across the servo track at a predetermined angle to the longitudinal axis of said servo tracks, com-prising:
a gap for reproducing signals prerecorded on said medium and for recording signals thereon;
a first pole piece;
a second pole piece cooperating with said first pole piece to form the gap with the outside edge of said second pole piece having a sharp configuration and being the lead-ing edge of the head; said second pole piece having a length-wise dimension substantially equivalent to the effective spacing between the servo tracks, at the angle of traverse, said measurement being along the direction of head motion;
and coil means seated on one of said pole pieces, for repro-ducing and recording the signals.

2. In a magnetic recorder wherein a recording surface is positioned relative to a recording transducer and said transducer is aligned with a selected data track by use of servo indicia in servo tracks located on said recording surface said transducer moving traversely across the servo tracks at a predetermined angle to the longitudinal axis of the servo tracks the improvement comprising in combination:
a recording means having spaced longitudinal servo tracks with servo indicia thereon and data tracks inclined to the servo tracks;

a transducer means, associated with said recording means, having a gap for reading and recording data and having a sharp leading edge;
said gap positioned so that the distance between the gap and the sharp leading edge of said transducer is substan-tially equal to the effective distance between the center-lines of the servo tracks, at the angle of traverse.

3. Apparatus for reducing defects in the reproduced servo envelopes of a recorder comprising:
a length of magnetic media having servo tracks thereon for track following and inclined data tracks;
said servo tracks are parallel to an elongated edge of said length of magnetic media;
a magnetic head, having a core geometry with a sharp leading edge a trailing edge and a gap therebetween, oper-ably associated for moving traversely across the servo tracks at a predetermined angle to the longitudinal axis of the servo tracks, said magnetic head having a spacing between the gap, and the leading edge substantially equal to b ? Sin .theta. where b is substantially equal to the spacing between the servo tracks and .theta. is substantially equivalent to the inclined angle of the data tracks.

4. An improved magnetic head, for a magnetic recorder in which track following is maintained from the amplitude of signals derived from prerecorded servo indicia located in servo tracks:
the magnetic head moving transversely across the servo tracks at a predetermined angle to the longitudinal axis of the servo tracks; said magnetic head having:
a center pole piece;
a first support relief being operably connected to said center pole piece;
a first gap being formed by the center pole piece and the first support relief;
first coil operably seated on said first relief;
a second support relief operably connected to said center pole piece;
a second gap being formed by the center pole piece and the second relief;
said second gap being spaced from the first gap a distance substantially equivalent to the effective spacing between servo tracks at the angle of travers; and a second coil being operably positioned on the second support relief.

5. The device as claimed in claim 4 where the first gap is a read and/or write gap.

6. The device as claimed in claim 4 where the second gap is an erase gap.

7. A magnetic transducer, for cooperating with a relatively moving recording surface in which longitudinal servo tracks are prerecorded and are used for accessing data in tracks inclined to the servo tracks, said transducer mov-ing transversely across the servo tracks at a predetermined angle to the longitudinal axis of said servo tracks, compris-ing:
a dual gap magnetic head;
said dual gap head having a center core pole piece for separating the gaps and having an effective separating dis-tance substantially equivalent to the spacing between the longitudinal servo tracks at the angle of head traverse.

8. The device as claimed in claim 7 wherein one of the gap's widths is such that a null in the gap loss function is being created at servo density.

9. The device as claimed in claim 8 wherein the gap width is being equal to approximately 581 microinches.

10. A dual gap magnetic transducer for use with an elongated length of magnetic media having adjacent servo tracks thereon, with servo indicia in said tracks, said transducer moving traversely across the servo tracks at a predetermined angle to the longitudinal axis of the servo tracks, comprising in combination:
a center pole piece;
a first support relief connected to said center pole piece;
a first gap formed by the center pole piece and the first support relief;
said gap having a predetermined width to create a null in the gap loss function at the density of the servo indicia in said servo tracks;
first coil operably seated on said first relief;
a second support relief operably connected to said center pole piece;
a second gap formed by the center pole piece and the second relief;
said second gap being spaced from the first gap a distance substantially equivalent to the spacing between servo tracks at the angle of head traverse; and a second coil positioned on the second support relief.

11. An improved magnetic head for a magnetic recorder in which track following is being maintained from the amplitude of signals derived from prerecorded servo indicia located in servo tracks.
the magnetic head moving traversely across the servo tracks at a predetermined angle to the longitudinal axis of the servo tracks, said magnetic head having a read gap and a core geometry related to said read gap selected in relation to the effective spacing between the servo tracks at the angle of traverse operable to shift unwanted servo envelopes to be in phase relationship with the main servo envelope which is being outputted from the read gap thereby reducing the effect of unwanted servo signals.

12. The magnetic head as is claimed in claim 11 where the unwanted servo envelope is being shifted out of phase and not to overlap the main servo envelope which is being outputted from the read gap.

13. The device as claimed in claim 11 wherein the magnetic head includes:
a center pole piece;
a first support relief being operably connected to said center pole piece;
a first gap being formed by the center pole piece and the first support relief;
first coil operably seated on said first relief;
a second support relief operably connected to said center pole piece;
a second gap being formed by the center pole piece and the second relief;
said second gap being spaced from the first gap a distance substantially equivalent to the spacing between servo tracks; and a second coil being operably positioned on the second support relief.

14. The device as claimed in claim 12 where the first gap is a read and/or write gap.

15. The device as claimed in claim 12 where the second gap is an erase gap.

16. A magnetic head as claimed in claim 11 for use with a relatively moving magnetic medium having longitudinal servo tracks and data tracks inclined to said servo tracks, said magnetic head moving traversely across the servo track at a predetermined angle to the longitudinal axis of said servo tracks, comprising:
a gap for reproducing signals prerecorded on said medium and for recording signals thereon;
a first pole piece;
a second pole piece cooperating with said first pole piece to form the gap with the outside edge of said second pole piece having a sharp configuration and being the lead-ing edge of the head; said second pole piece having a lengthwise dimension substantially equivalent to the effec-tive spacing between the servo tracks, at the angle of traverse, said measurement being along the direction of head motion; and coil means seated on one of said pole pieces, for reproducing and recording the signals.