Dual-Track Spiral Recording and Associated System

The subject invention relates to magnetic disk recording systems and particularly to "spiral" track recording therewith.

Those in the magnetic recording arts recognize the need for improved techniques and associated apparatus for better, more effective data detection. Efforts have continued for sometime now to fill this need.

One conventional type of recording system involves "concentric track" recording where a magnetic disk [typically used as peripheral memory equipment in a computer system to provide temporary or permanent information storage during computer operations] is recorded-upon in concentric tracks. In one well-known configuration, one, or several, such disks are mounted to be rapidly rotated in operative relation with transducer means, the disk having a multi-track magnetic recording surface on at least one of its faces. One, or several, recording heads are, in turn, adapted to be positioned along each disk-face--i.e., to register with any selected one of the concentric recording tracks on the disk to record and detect data signals along any track.

Workers will recognize that optimal use of such media requires that information be recorded with minimal effort and at the highest possible density. However, concentric-track disks--unlike tape--present the problem of "limited-length record fields".pi.(or "closed-ended fields") whereby the defined (circumferential) length of a given track usually compels one (e.g., a Programmer, a User, the Designer) to either waste "terminal space" or interrupt a data field which happens to occur there. For instance, if a given track fills up with data fields until only a fifty-bit segment remains and the next convenient record subset to be recorded is 60 bits long, one must either shift to another recording track (wasting this 50-bit space), or interrupt this 60-bit subset; paying the usual price in "overhead" (e.g., added bits to note the interruption, identify the continuation, etc.; and the added complexity in software labor, etc.).

But, with tape, or any like record offering "open-ended fields", this problem will not arise (except in rare instances; e.g., at "end-of-tape"). This invention is directed to providing spiral track disk recording which offers such "open-ended fields" and other advantages.

Workers will recognize that, for the typical magnetic disk system, a recording head is translated radially across the disk so that the magnetic transducer gaps mounted therein may be selectively positioned adjacent a selected recording track. In this way only a few transducer gaps need be used for recording and reading data on a number of disk tracks--but to practically implement such a system, one must maintain very precise control of head location relative to the tracks--and this typically must be done very quickly to minimize access time for the computer system served.

For instance, with disks used in a random access magnetic memory the data bits are recorded in concentric circular tracks so there is a continual need to secure and maintain very accurate registry of a magnetic transducer with a selected track. Unfortunately, the precision of the transducer-positioning system will determine track spacing tolerances and accordingly will influence data storage efficiency (bit compression) significantly--that is, the number of characters per unit memory area will depend upon the accuracy of transducer positioning. Workers have attempted in various ways to improve the accuracy of transducer positioning, for "servoing" the transducer onto disk tracks. Such systems have commonly employed "position signal" tracks (or track sectors) interspersed with the data tracks and have also required a special servo transducer detector to detect the "position-signals". Other approaches use "track-on-data" techniques (e.g., see Parent U.S. Ser. No. 807,155 cited above). This invention can allow one to avoid all inter-track re-positioning difficulties by adopting "spiral" recording--whereby, once a track is located, one merely "follows" the track for n revolutions, keeping centered thereon.

Workers in these arts will recognize that it is quite desirable to "track-on-data", that is to somehow use an area devoted to "data-bits" (i.e., "information signals" developed from certain magnetic transitions) to also provide position control signals which may be fed to a positioning servo and control the positioning and/or alignment of a transducer relative to a recorded track. Obviously, such a technique can eliminate the need for a separate "servo" recording unit and related separate recording zones for servo data (such as separate servo disks or separate servo tracks, or track-sectors, typically seen in conventional magnetic recording systems), since the data-transducer and the data-recording zones may be used for servo-bits too. The invention accomplishes this, providing a "spiral" mode of recording with "track-on-data" capability (e.g., as opposed to other methods of centering--see parent Ser. No. 807,155 for citations to some such), with no need for separate servo tracks and providing a "servo transducer" which is integrated with a "data transducer", with servo-bits being incorporated into the data recording zones as desired.

The present invention is a significant improvement over prior related techniques, teaching the use of a "multi-gap" transducer array adapted for spiral recording--e.g., with a gap pair oriented to be mutually orthogonal, as well as disposed "in-line", along the track-direction (hereinafter these are called "di-gaps"). These gaps are adapted to conjunctively read two different kinds of (data/servo) bit sets arranged along the track--with one kind of bit aligned with one such gap, and the other kind at right angles thereto, to be thus aligned with the other gap. The servo-bit locations may indicate head-misregistration and, as detected, do so in terms of elapsed time between prescribed servo signals along any given track. Preferably, the invention is implemented with a radially-aligned, "dual-gap" array adapted to track skewed, orthogonal bits simultaneously along a pair of spiral tracks.

According to one feature, systems according to the invention so function without inter-track "guard-bands" or the like; disposing adjacent data tracks in abuttment with one another. Also, the magnetic data transitions are skewed in parallel along one track, while being transversely skewed (--orthogonal to these first transitions--) along both flanking tracks. As explained, this can minimize adjacent channel interference and can also dispense with the need for such things as "guard-bands". According to one embodiment, servo positioning signals are interspersed among data-bits and detected with a single "di-gap" transducer head. ["Di-gap "V" head" hereinafter referring to a pair of positionally-related, track-aligned, magnetic transducer heads, each head comprising a pair of pole pieces separated by a transducing gap and wound with an associated coil-activation circuit--though the windings and one pole-piece may, of course, be shared].

Of course, others have contemplated the use of "orthogonal data tracks" (e.g., see the cited Sippel patent). Likewise, others have thought about monitoring head registration according to the alignment of a transducer gap relative to an array of parallel magnetic domains arranged diagonally across a recording track (e.g., see the "herringbone" servo tracks and related detection technique taught in U.S. Pat. No. 3,686,649 to Behr). Also, others have a kind of spiral recording on disks--e.g., as with the spiral audio tracks on a phonograph disk record.

However, the instant "spiral/track-on-data" arrangement will be distinguished as novel and unexpectedly effective, combining the oblique "herringbone" track pattern and "servo bits" (registration "di-bits") with spiral recording--also preferably with centering effected by sensing head registration along a data track--the di-bit pattern being sensed by an associated "di-gap" head--e.g., preferably with one ("servo") gap thereof being adapted to detect a shift in lateral head position (misregistration) according to a varying time interval between detected servo signals. (E.g., between a reference servo signal and a variable servo signal). Of course, workers have heretofore suggested orthogonal skewed data tracks along a magnetic record, as well as superposition of recording transitions (e.g., U.S. Pat. No. 2,929,670 to Garrity). However, it will be seen as novel to so use spiral recording with (one or more) multi-gap heads, allowing either servo data or work data, or both, to be transduced by either or all gaps.

In a preferred embodiment for instance, the work-bits are impressed "skewed", at a prescribed angle oblique to track direction, while servo-bits are arranged along the same track with their magnetic domains aligned transverse to these "work domains" and disposed at prescribed regular intervals along the track. Such work-bits and servo-bits are oriented to interact with a common double-gap transducer unit, with both magnetic gaps registered along the selected track, and with one gap aligned parallel to the work-bits, the other parallel to the servo-bits. Such a system obviously maintains a fixed spatial relation between data transducer and servo transducer in a very simple convient fashion, as well as keeping them inherently synchronized (that is, they traverse the medium at the same speed and direction).

According to certain embodiments this arrangement is capable of easily providing "registration feedback" along the entire length of a spiral track. That is, with this technique and associated apparatus, the multi-gap transducer head may be registration-referenced to the contemplated magnetic recording medium (moving along a prescribed direction), and may be repositioned for centering therealong.

At least one gap pair is used, with the paired work gap and servo-gap both skewed with respect to track axis and transverse to one another. The servo output is coupled to a head-positioning arrangement adapted to reposition the gap pair radially on a disk for centering over a selected track. Preferably, the servo-bits, (head positioning information) as well as "work-bits", are both recorded along the same track, so that the work-bits pass in alignment with one of the transducer gaps, while the servo-bits align parallel to another gap.

Thus, once the di-gap head is registered on a given track its gaps should register with the servo-bits and the work-bits respectively so as to generate respective servo signals and data signals. According to this feature, either gap may handle either signal.

Preferably, the gap sensing servo-bits will provide a servo output reflecting the time interval between successive servo-bits--this, in turn, reflecting any shift in head position to the left or right of the track center line. Preferably, the servo signals "follow" the transit time of the head; accordingly, the servo output may be interpreted as a distance-indicating signal whose variance from a prescribed norm (representing perfectly registered, or centered, head over a subject track) represents the lateral head variance or misregistration, and thus may be used to cause a responsive servo system to reposition and center the head (known systems which seek a "zero error" feedback signal). Such a servo output control over the radial positioning of the head can be implemented, using conventional servo means, as known in the art.

Such a servo output may be especially apt for maintaining head registration with a "spiral track" (or any other disk track which varies in radial position as a function of rotational position)--e.g. the servo output being continually compared with a reference signal representing "registration" (centered alignment of the head along the track--e.g., via "Table-Lookup") to derive a servo controlling "difference signal" controlling the servo to reposition the transducer leftward or rightward and so reach a "zero-error" position (i.e., registration).

Preferably, such an arrangement is used with disks having "adjacent abutting" data tracks with data bits aligned oblique and parallel along a track and orthogonally between tracks, with a respective pair of transducer gaps disposed "in line" to be translated along a selected track either, or both, gaps to develop both data and servo signals therefrom.

More preferably, the invention is implemented by a "dual-track" spiral recording technique.

These and other features and advantages of the present invention will be appreciated by workers as they become better understood by reference to the following detailed description of the present preferred embodiments which should be considered in conjunction with the accompanying drawings, wherein like reference symbols denote like elements.

FIG. 1 is a very schematic plan view of a magnetic disk record with a simple "non-spiral" record track indicated as position encoded according to one embodiment; FIG. 1A showing an enlarged area of the disk as disposed relative to a di-gap transducer provided according to the invention;

FIG. 2 indicates a single record track, encoded by position and disposed relative to associated transducer indicia according to a related feature; while FIGS. 2A, 2B, and 2C indicate suggestive transducer dual-outputs for three illustrative transducer positions;

FIG. 3 illustrates a fragmentary plan view of a portion of another like magnetic disk record, greatly enlarged, with adjacent tracks and magnetic domains, including "another position" indicia embodiment therein schematically indicated in positional relation with an associated "di-gap" magnetic transducer; an enlarged showing of one of these tracks and the associated transducer being indicated in FIG. 3A and related indication of illustrative transducer outputs in FIG. 3B;

FIG. 4 illustrates, in plan view and greatly enlarged, a schematized fragmentary showing of a set of tracks like those in FIG. 3 as related to "double di-gap" transducer means and data bits indicated according to another array;

FIG. 5 is a schematic block diagram of a utilization system adapted for "di-bit/di-gap" arrays like the above;

FIG. 6 is similar to FIG. 2, indicating a modified form of position-encoded indicia and associated transducer gaps along a track;

FIG. 7 is a plan view of a disk record as in FIG. 1, schematically indicating a related mode of recording position bits;

FIG. 8 illustrates "single (di-gap) head/single track" spiral disk recording according to one propaedeutic embodiment; with a modified "2-track head" in FIG. 8A; and

FIG. 9B illustrates, in similar fashion, a related "dual di-gap head/dual track" spiral recording according to a preferred embodiment, with a similar multi-track embodiment in FIG. 9A.

FIG. 1 schematically illustrates a magnetic recording disk D constructed according to principles of this invention. This, and other magnetic recording means discussed herein, will generally be understood as constructed and operating as presently known in the art, except where otherwise specified. Such a recording disk is relatively conventional, being about one foot in diameter and formed of a non-magnetic substrate material with a thin magnetic recording medium applied to one face.

Such disks are commonly mounted on a turntable which is seated on a precision-bearing spindle and rotated at high speed during operation. Thus, every bit along any selected circumferential track (see illustrative recording tracks T-1, T-2 and T-3 in FIG. 1A) is swept past magnetic transducer means (here, see transducer head "h" on arm TT) many times a second for minimum access time and high speed read-out. In a commercial disk unit, one or several such disks is employed, each having one or several transducers per disk. Conventionally, record information ("work-bits") is recorded along the data tracks. One or several servo-transducer means is often provided and arranged to be operated in conjunction with special servo-tracks (or track-sectors) on which servo-data (servo bits) is recorded.

The rotational rate (rpm) of disk D is normally carefully controlled so that any small relative change in rotational speed is quickly corrected and so the magnetic reading and writing operations are kept constant. Conventionally, the rotational position of the disk is indicated by angular encoding means, clock tracks, index indicia (e.g., hole "ih" along "start radius, SR", FIG. 1), or the like. Such features are conventional and not detailed here since they are not of special significance in practicing the invention.

This servo information is used to align a transducer head (here, see head "h" mounted on transducer-translator unit TT and conventionally positioned thereby) radially of disk D, i.e., with its transducer gaps registered with a given selected track on disk D, using means well known in the art (and not shown or described here). A reference radius is conventionally indicated by passage of an index indicium over a related detector (e.g., here, see index hole "ih" along "start radius"SR). Complicating this servo function are the typical deviations of disk tracks from perfect concentricity (with one another and/or with their disk). This is indicated by tracks T-i, T-ii which will be understood as out of concentricity, both with disk D and with reference track T-2.

Representative tracks of disk D are fragmentarily shown--exploded and with recording bits also illustrated--in FIG. 1A along with an enlarged, very schematic showing of head "h", understood as adapted for recording and detection of such bits.

As is conventional, it will be understood that work bits in the form of magnetic signals "wb" are recorded on the face of disk D by a transducer-gap provided in the transducer array (here, represented by either of the gaps "g" of "di-gap head" "h") which is appropriately positioned. Head "h" will be understood as coupled mechanically to a positioning unit (not shown) including position-actuator means arranged and controlled so that transducer "h" is translated radially across D to be operationally superposed over a selected track (very schematically indicated by head translation arm TT and generally understood in the art, hence no details are indicated or necessary).

Thus, for example, the position control can comprise a so-called "voice coil actuator", i.e., a magnetic positioning device very similar to that employed in loud speakers. Such actuators are generally preferred because they are inexpensive, fast, accurate and readily controlled with conventional circuitry. However, if desired, other mechanical, electromechanical or hydraulic positioning control means may be employed, as is well known in the art.

Work-bits "wb" will be understood as recorded along the disk tracks by appropriate energization of the related magnetic transducer gap in head "h", and to comprise a sequence of magnetic transition signals of identical encoded magnetic polarity and alignment. Here, preferably, and according to a feature aptly employed with the invention, work-bits "wb" are impressed at a common prescribed angle to be all similarly oblique with respect to the respective track axis A.sub.t. (The direction of translation of the track with respect to the transducers).

According to one feature, a bit encoding scheme establishes, for each track, a prescribed alignment for work-bits and for servo-bits, this alignment being arranged to automatically indicate registration, or centering, of transducers with respect to a track). For instance, for tracks T-1, T-2, T-3, etc., in FIG. 1A, it will be understood that the work bits "wb" are aligned in one oblique direction along all "odd-number" tracks (e.g., T-1, T-3) and aligned transversely in all "even-number" tracks (e.g., T-2). The servo-bits "sm" are aligned semi-orthogonal to the work-bits along any given track. Bits "sm" will be characterized as "centering di-bits" as explained below and will be understood as "LAMBDA-configured" relative to the track--i.e., like "A", as for a Greek (capital) LAMBDA (or like its inverse: "V"; e.g., in contradistinction with "tilted-V" marks, or "<",">"--such as shown in U.S. 4,074,328 to Hardwick).

These recording tracks will be understood as schematically represented here by a mere sector of the full disk/track circumference; there being a great number of such tracks understood as concentrically arranged, in abuttment, on disk D. Each of the concentric recording tracks is distinct in location, length and curvature and the transducer and associated gaps must be very precisely registered thereon before writing or reading may be properly performed--as workers in the art very well know.

Thus, in order to position a transducer gap in operative (read/write) relation above a selected track, the position of the transducer head must be detected and checked for "centering" along this track. Conventionally, a raw position signal would be compared with a reference signal which represents the "centered" (or registered) head position. Any discrepancy between these indicates the degree of misregistration and is processed to result in an "error signal" fed back to a position controller (in a conventional servo loop) for precise repositioning and control of the head.

In some known systems, track location is indicated by "servo-bit" magnetic transitions provided along special dedicated servo tracks, of a disk. In one well known system, such servo-bits are recorded along special servo tracks disposed between adjacent data tracks, as suggested, for instance, in the cited U.S. Pat. No. 3,686,649 to Behr. By contrast, in the subject embodiments, the data tracks are abutted (radially) with the bits aligned to be orthogonal between adjacent tracks--doing away with intervening spaces for servo tracks, guard-bands, etc.

Such a "radially-abutting" track configuration will be recognized as facilitating maximum track density. However, this makes it necessary to record servo information bits along a portion of the data tracks. It also makes it critical that the read/write gaps be positioned very accurately, since a transducer gap might otherwise easily drift over an adjacent recording track. These requirements are met in systems according to the invention, with a "di-gap/di-bit" servo control described hereinafter. That is, a transducer is provided with a pair of skewed orthogonal gaps, [such as gaps g.sub.1, g.sub.2 of head "h" in FIG. 1A]; and related servo bits are recorded to comprise at least one pair of similarly-skewed, mutually-orthogonal servo-bits [such as servo-bits "sm" in FIGS. 1 and 1A].

FIG. 1:

Turning to the details of FIGS. 1 and 1A, the indicated magnetic transducing arrangement will be understood as adapted to operate upon the abutting concentric data tracks T-1, T-2, T-3, etc., of a magnetic recording disk D, when the disk is rotated in the known manner. Servo-bits "sm" in the form of skewed, mutually-orthogonal di-bits will be understood as distributed in a prescribed manner along each given track T, being inserted among the work-bits "wb", along with (track/sector) identifying bits "sb". Work-bits "wb" are aligned in parallel, and similarly skewed, along every track, being "orthogonal" between adjacent tracks (i.e., they are "skewed and adjacent-orthogonal"). This magnetic information will be understood as conventionally recorded and sensed. Such is indicated suggestively by "di-gap" read/write head "h" adapted to be moved radially across disk D to any selected track-location where the transducer gaps will lie superposed above a "selected" track T and centered therealong in close "read/write relation" therewith (see FIG. 1A).

According to one recited feature, head "h" includes at least one "di-gap" array; i.e., a pair of skewed orthogonal gaps g.sub.1, g.sub.2. Head "h" has a width w.sub.h approximately equal to the (uniform) radial width of w.sub.t of the tracks. Thus, when head "h" is moved into prescribed registration (exactly-centered relation) with a given track T, one of its gaps "g" will align and superpose coincidently with one set of bits (--either "wb" or "sb"; or one half of di-bits "sm", these bits extending across the track in a "first" skew-alignment--) while the companion gap will be similarly aligned with a second set of bits orthogonal to the first. Thus, gap g.sub.1 in FIG. 1A, passing along track T-4, (or any "even-no.-track") aligns with "track-sector identifying" bits "sb", and with one of the servo di-bits "sm", while the other gap g.sub.2 will align with work-bits "wb", and with the other half of di-bit "sm". Conversely shifting head "h" to be centered along track T-1 (or any "odd-no.-track") will reverse this registration-relation, e.g., g.sub.1, aligning with the work-bits "wb", there.

The "magnetic congruency" of such a di-gap transducer and such servo di-bits, (or "chevrons") when a head is centered over a recording track will be seen as facilitating advantageous serve control--with the degree of off-centering, or misregistration, being sensed according to how closely such a di-bit "fits" the passing di-gap--as further described and explained below. This concept will also be better understood upon consideration of the alternate arrays in FIG. 2 described as follows.

FIG. 2:

Here, a "di-bit" data track T' is shown in operative relation with an associated "di-gap" transducer assembly TR' understood as passing over representative track T' in the direction of the arrow, in magnetically operative relation with bits A, B, therealong, but in slight misregistration, with respect thereto (misregistered "to the left"). Transducer TR' thus includes a pair of skewed, mutually-orthogonal transducer gaps g.sub.a, g.sub.b aligned oblique (here, preferably 45.degree.) to the axis of track T'. Track segment T' may be understood as a servo-sector like these indicated in FIGS. 1, 1A with similar "di-bits", comprised of relatively orthogonal first and second di-bit-halves, (i.e., magnetic recording half-bits A and B respectively, analogous to servo di-bits "sm" above). Di-bits A, B will be understood as each aligned with a respective transducer gap (g.sub.a, g.sub.b) and thus orthogonal to one another and oblique (also 45.degree., preferably) to the track direction (arrow). Track sector T' shows only servo bits and no work-bits, and is here represented as "linear" rather than "curvilinear" (as the actual face of a magnetic recording disk would be)--but only to simplify the explanation. Those skilled in the art will obviously extend the principles explained to curved disk tracks, and other relevant media, including work-bits too, as a matter of course.

Now, it should be understood that the relative disposition of the bi-bit pair A, B and gaps g.sub.a, g.sub.b (their spacing and relative angular orientation) is such as to render "magnetic congruency" between a bit and a respective gap when head TR' is centered exactly (registered) along track T'. Thus gap g.sub.a will coincide with bit A and gap g.sub.b will coincide with bit B at a certain time during track passage--and the detecting transducers will thereupon generate a corresponding pair of coincident opposed "servo-output" pulses. A relatively perfect congruence of di-gaps and di-bits is signalled in FIG. 2B by the simultaneity of symmetrically-opposed pulses P-A, P-B representing detection of bits A-1, B-1, etc., by head TR'; pulse amplitude may be equal, but this is not always necessary, though it facilitates a "null-balance" indication of perfect registration, of course, as workers will recognize). This opposite polarity output is readily rendered by known methods.

On the other hand, a slight misregistration of head TR' to the left, as depicted in FIG. 2, should produce the kind of (successive, spaced) non-coincident output pulses indicated in FIG. 2A wherein pulse P-A' (produced by passage of gap g.sub.a over bit A-1) will obviously occur somewhat earlier in time than the companion output pulse P-B'--P-B' reflecting the later passage of gap g.sub.b over companion bit B-1. And, the time-discrepancy +.DELTA.T.sub.L) between output pulses will be a measure of the degree of head misregistration (the positive sign indicating misregistry to the left), as workers in the art will appreciate.

Conversely, rightward misregistration of transducer TR' is signalled in FIG. 2C (such head misregistry not shown here, but indicated schematically by "phantom bits" A"-3, B"-3 in FIG. 2) by the non-coincident servo (timing) pulses P-A", P-B". Here, output pulse P-B" from gap g.sub.b "leads" output pulse P-A" from companion gap g.sub.a by a time delay (-.DELTA.T.sub.R) which corresponds to the degree of rightward misregistration (and accordingly is designated as negative delay time).

Workers will visualize other like arrangements for correcting head misregistration wherein transducer di-gaps align oblique to the transport direction can likewise interact with associated (similarly oblique) di-bits so that exact head/track registration is indicated by coincidence of the paired output pulses, while misregistration is indicated by positive or negative non-coincidence. In certain cases such servo-bits may, themselves, constitute work-bits ("record data"), especially where the work-bits are skewed 90.degree. between adjacent tracks (as in FIGS. 1 and 2).

This is indicated very schematically in FIG. 4 where segments of abutting adjacent disk tracks T-a, T-b, T-C, T-d, T-e is depicted as comprising skewed work-bits "wb" which are "orthogonal adjacent". According to this feature, periodically a high-frequency burst of "special-bits", hfb, hfb'--similarly skewed--are laid down for head-centering purposes. Workers will appreciate that bits hfb, hfb' may substitute for di-bits like "sm" above. It will be evident, that, according to another mode of "di-gap/di-bit" operation a transducer such as TTR with at least one related di-gap pair (see orthogonal gaps g.sub.a, g.sub.b) may be provided, with the gaps spaced "across tracks" (rather than "along a track" as above) by a prescribed (odd) number of track widths (here, three--this distance accommodating reasonable gap spacing and head manufacturing tolerances). Di-gap g.sub.a, g.sub.b will sense the high-frequency bit pair hfb, hfb' coincidently as an indication that head TTR is perfectly centered over tracks (T-b, T-e); non-coincidence indicating misregistry, as before.

It will be evident that the di-bit pair can be variously offset in space (e.g., by offset spacing dd-g, the same as offset d-g between gaps g.sub.a, g.sub.b) or offset in time (electronically)--gap-to-bit coincidence being provided for either spatially or electronically. Of course, such "work-bits" may be otherwise modified and distinguished to thus serve as "servo-bits"--for instance, written as "invalid bits" (e.g., preceded by three or more (3+) "zeros") or as "special bits".

Also, the head TTR may include a second orthogonal gap pair (here, g.sub.c, g.sub.d) to accommodate the sensing of work-bits in other tracks (e.g., T-a, T-c, T-e for g.sub.c ; T-b, T-d, etc., for g.sub.d). These second gaps are not needed however and will typically be included only where cost-justified.

Similarly, one oblique gap may be translated along such a track to detect certain aligned servo bits and to generate servo-positioning pulses, with these pulse signals "referenced to center" according to their degree of coincidence with a prerecorded set of "clock signals". The servo output may be time-referenced to such clock signals (indicating "center-track registration" of the servo gap) and thus eliminate the need for contemporaneous detection of a second servo-bit with a second orthogonal gap, as described above. In certain cases (e.g., FIG. 1A) part of a track-sector will include only servo-bits, with abutting "blank track segments " flanking the sector radially, to eliminate risk of noise. This is preferred for this "track-on-data" operation and maximizes data compression.

In any event, the foregoing techniques will be appreciated as facilitating a true "track-on-data", or "servo-on-data" operation, locating the servo-bits directly adjacent their associated data bits and avoiding the difficulties and errors of remotely-located servo indicia.

Operation:

The operation of the arrangement of FIGS. 1 and 1A, will, in general, be apparent from the foregoing; and, in any event is particularized in the cited U.S. Ser. No. 807,155 incorporated herein by reference.

Workers will appreciate how simple such a servo centering technique is and how it assures that the head is centered over a track before any read-out may begin. This maximizes the gap/bit congruency and the associated accuracy and efficiency of bit detection and/or writing, while at the same time accommodating maximum track density with less concern for head misalignment.

More particularly, a known digital servo system may be set to invoke a certain number of "positioning steps" when translating head "h" fully across a track width (e.g., 30 steps to cross a bit-track completely). And a "centered" limit may be set such that a certain minor misregistration is tolerated (e.g., up to 3 servo steps, or the "time disparity" T.sub.L between di-gap output pulses which corresponds to this, as indicated in FIG. 2 above).

Workers will recognize that servo response to the misregistration (of the di-gaps with the servo di-bits) detected may be a relatively gradual and continual thing. That is, with many sectors and associated sector-preambles normally occurring along a given track, the servo positioning means may be referenced to "coincident di-gap output" several times per disk revolution, with head "h" being responsively "recentered", to some extent, each time a servo di-bit passes. This facilitates a smoother, more gradual and continuous, "centering" mode as workers will appreciate. It also helps to compensate for disk eccentricity and "run-out" along any given track--something quite complex and difficult to accommodate with conventional means.

Eccentric tracks:

Workers will recognize various applications of the above features; for instance, when tracks are recorded in parallel about a disk to be out of "concentricity" with the disk somewhat. Such "eccentric tracks" are familiar to workers and occur not infrequently (e.g., due to local variations in turntable/shift alignment, etc.). Such are illustrated by eccentric tracks T-i, T-ii, in FIG. 1.

A solution to this problem, along the lines taught is suggested in FIG. 7 where a pair of di-gap heads h.sub.1, h.sub.2 are mounted in tandem to simultaneously operate on two respective tracks on a disk DD--one track T-1 being one of several carefully centered "prerecorded servo tracks" (or sectors); the other being a new data track (e.g., T-a), whose concentricity is to be assured. Accordingly, it will be evident that head h.sub.2 may be "slaved" to head h.sub.1 and be servo-centered therewith, so that when head h.sub.1 is registered on a "control servo track" (or track segment T-1, using di-gap/di-bit sensing as taught above), head h.sub.2 will "follow" and write a related data track which is concentric with T-1 and with disk DD (e.g., T-a "slaved" to T-1, T-b slaved to T-2, etc.). Further, a "bootstrap mode" may be used whereby certain other new data tracks are, in turn, likewise "slaved", during writing, to (the position of) a respective "first-written" data track (e.g., T-n and head h.sub. 2 slaved to T-1 and head h.sub.1).

Min/max misregistration:

A maximum tolerable misregistration may be built-in to the system by limiting the minimum acceptable amplitude of the servo di-bit read-out. For instance, a 50% misregistration (or 15 "servo-steps" misregistry as above) might be the maximum centering error tolerable; in such case the gaps would be "straddling" two adjacent tracks and the nominal amplitude of the servo read-out pulse corresponding to this might be about 50% of the maximum "fully-centered" read-out amplitude.

In such a case, (and in any instance where a head is so "straddling") the servo control program might be set to arbitrarily command the head to take predetermined corrective action (e.g., "move radially-out ten steps and begin a new centering sequence"). In a related situation, if satisfactory centering were achieved over the wrong track; then upon reading the track number (sensing bits "sb") this would be discovered and no harm done (e.g., no erroneous data readout would be accepted)--instead, an entirely new "coarse positioning" step could be invoked to re-new the search sequence for the correct selected track. Workers in the art will conceive other conventional ways of handling similar problems using the invention

Workers will also conceive other ways of employing such servo di-bits. For instance, as described below relative to FIGS. 3 and 3A, one or both oblique portions of a servo di-bit may be interspersed with, or "over-written" upon, work-bits.

FIG. 3:

A modified, further improved way of using a skewed orthogonal di-gap transducer, together with similarly-skewed servo-bits is indicated in the array of FIGS. 3 and 3A Here, a rotatable magnetic disk record D is shown very schematically, with abutting recording tracks (e.g., T-1, T-2, T-3) along which indicated "work-bits" "d" may be recorded as above. Bits "d" will be understood as aligned in parallel oblique to the transport direction (arrow T-A.sub.X) and orthogonal between adjacent tracks. A series of "singular" skewed servo-bits "smm" (not di-bits) are here "written-over", or interspersed among, certain work-bits "d" and orthogonal thereto according to this feature. A di-gap head TR may be used for transducing as before.

Workers will appreciate such a "track-on-data" scheme--with a di-gap head operating on "di-bit tracks" (here, the servo-bits and work-bits cooperate--not pairs of servo-bits) as quite new and advantageou--and one that may be implemented in various ways. The magnetizations represented by these bits and their respective magnetic direction are (as above), indicated schematically by the parallel lines "d", "smm". The "orthogonality" between bits may be visualized as a 90.degree. rotation of the magnetic axis of the pre-magnetized domains on the virgin substrate.

Except as otherwise described disk D and associated di-gap head TR (with skewed orthogonal gaps g, g' and accessories, like access arm AA, etc.) will be understood as conventional and similar to those described above with respect to FIG. 1. Thus, the orthogonal skewed transducer di-gaps g, g' are disposed and adapted to be aligned in "magnetic congruence", or registration, with either of bits "d" or bits "smm" (head TR having a width w.sub.h approximately equal to the width w.sub.t of the tracks T). Thus, bits "smm" indicated in phantom in FIGS. 3, 3A will be understood as impressed in a prescribed manner over a track sector corresponding to a prescribed plurality of transverse work-bits "d" (--rather than being allocated to separate tracks and/or to separate portions of a data track). Here, servo-bits "smm" span four (4) work-bit sites, for example.

As mentioned above, bits "d", "smm" are skewed, i.e., with respect to "translation axis" T-A.sub.X, at angles .phi. and .phi.' respectively (these preferably being +45.degree. and -45.degree. with respect to TA and thus transverse to one another) and are at right angles with like respective bits from "track-to-track". Such an "adjacent orthogonal/transverse within track" bit array has been described above. Accordingly, as head TR moves radially across disk D, it will be understood as traversing successive disk tracks to stop "semi-registered" over a selected track; then the bits "d", "smm" will be detected by the passing gap that happens to be aligned therewith and "fine-registration" will follow.

Thus, for instance, when head TR is positioned so that gap "g" overlies track T-1 it will be relatively perfectly aligned to record and/or read work-bits "d" with maximum efficiency (being parallel thereto and "magnetically congruent" when superposed)--while companion gap g', aligned transverse to gap "g", will accordingly be oriented for no significant magnetic interaction with bits "d", and for maximal interaction with bits "smm" (gap "g", in turn, being relatively unresponsive to bits "smm"). Likewise, shifting of head TR to overlie track T-2 will reverse the operative sense of gaps g, g' so that gap g' is uniquely operative with data bits "d", (which are orthogonal to the work-bits "d" along track T-1), while gap "g" lies in exclusive operative alignment with servo-bits "smm". Shifting again to register TR along track T-3 will again reverse the operative senses of the gaps (so they are the same as for T-1).

Workers will understand that the recording and reading is performed conventionally, with narrow magnetic gaps g, g' traversing domains in switching-relation so that if a domain ("bit") is aligned relatively parallel to a given gap and translated there-past in "magnetic congruence", a full-scale read-out signal will be induced from the associated transducer reflecting this passage. The polarity of the induced signal will depend, of course, upon the direction of change of magnetic transition.

According to a feature hereof, the distance interval between a pair of adjacent servo-bits along a given track (see interval S between bits "smm" along track T-1 in FIG. 3) will correspond to a prescribed "reference interval", reflecting a prescribed controlled head/disk velocity. When a perfectly registered (or centered) transducer proceeds along the subject track at the prescribed constant speed, servo output pulses "sop" will issue at prescribed times. These times may be represented as t.sub.0 +t, (t.sub.0 +t.sub.1, t.sub.0 +t.sub.2, etc.) reflecting the position of servo bits "smm" with respect to a fixed standard (e.g., Start Radius SR, see FIG. 1; as shown in the art--to indicating radius SR). According to a feature hereof, misregistration of the transducer gaps may be detected in terms of time-variations from these "reference times" sensed from associated output servo signals (e.g., t.sub.0 +t.sub.1 +t.sub.v ; t.sub.0 +t.sub.2 +t.sub.v, etc.).

Such a misregistration is very schematically indicated in FIG. 3A where transducer gaps g, g' of head assembly TR are misregistered "leftward" of track T-1 (assuming the gaps pass in the direction indicated by the arrow), or displaced "radially outward" of disk D. Track T-1 will be understood to include work-bits aligned to be sensed by gap "g", plus transverse servo-bits "smm" aligned to be sensed by gap g'. Such "leftward misregistration" of head TR will be noted as causing gap g' to intersect (a portion of) servo-bits "smm" somewhat "late" and produce an associated servo output pulse "later" in time (delay .DELTA.=+t.sub.v) than the case where gaps g, g' are centered exactly along track T-1. Conversely, "rightward" misregistration of gaps g, g' would cause the g' output to occur "sooner" (delay .DELTA.=-t.sub.v). Comparison of either such misregistered servo output pulse with a train of "reference pulses" representing the "centered head" (or registration) condition, will yield a time difference value .+-..DELTA.t which may be used to determine the direction, and degree, of misregistration--as workers can visualize (see FIG. 2 description details).

Workers will recognize that such an "orthogonal" magnetic "overwrite" of servo-bits (upon work-bits will, if the bits are substantially orthogonal), render each bit type uniquely responsive to only one of the di-gaps and magnetically isolated from the other bit type. That is, as workers in the art well know, a bit disposed transverse to a transducer gap is relatively "de-coupled", magnetically therefrom and non-responsive thereto. Also, adjacent orthogonal magnetic domains have relatively little significant magnetic interaction with one another.

For instance, consider bit "smm", in FIG. 3A: the net effect of its magnetic domains will be to produce a relatively strong magnetic output signal (sharp magnetic transition when gap g' passes over "smm" in operative magnetic relation or "magnetic congruence", therewith), while being relatively isolated from (no significant magnetic interaction with) "orthogonal" magnetic domains "d" and essentially, "ignored" by passing orthogonal transducer gap "g" (no output induced therefrom). Conversely, gap "g" will produce no significant servo output signal from the passage of bit "smm"; but only from passage of "d".

Restating this from a somewhat different viewpoint, the instant a servo-bit "smm" passes in perfect registration under gap g', it will (momentarily) essentially "fill" the gap 100% with magnetic flux from its magnetic domains (--here aligned in an East-West direction, and constituting an "E-W flux").

The transverse magnetic domains "d", will (especially if they are widely spaced so that only a few intersect bit "smm") present a transverse ("N-S") flux--a flux that fills only a relatively small portion of elongate gap g' (here the "servo-gap"). And their transverse ("North-South") magnetic alignment will have little or not interaction with the "smm" (E-W aligned) domains. As a consequence, bits "smm" will be relatively "isolated", magnetically, from bits "d" along the track; also bits "smm" can generate a servo output, upon passage of gap g' that is relatively independent of bits "d" and of associated "work gap" "g".

Workers may wonder whether misregistration of the transducer head can seriously degrade read-out from a "selected" track and/or introduce "error signals" from bits along the adjacent track--since the tracks are abutted together. For instance, in the embodiment of FIGS. 3, 3A, misregistration of gap g' to the right (or radially-inward from T-1) would overlap track T-2. This would likely a attenuate the "T-1 servo output" (from servo-bits "smm" along track T-1,--to the extent g' is out of "congruence" with gap g') as well as erroneously induce a pick-up in g' from work-bits "d" in adjacent track T-2 (--to the extent they register with g').

But, workers are quite familiar with known techniques adaptable to distinguish such servo-bits from such work-bits. For instance, the work-bits may be recorded at a particular high frequency, and/or be spaced closer together than servo-bits. In such a case the work-bit read-out can readily be filtered-out by conventional frequency discrimination techniques--the servo-bits along a given track being referenced to a prescribed known "reference spacing" (timing interval) and thus identified from the raw output pulses. (e.g., the mentioned "reference pulses" from the index hole could be used for this). Also, (as above mentioned) MIN-amplitude discrimination can set a limit on which signals are accepted after such misregistration.

By contrast it will be appreciated that servo di-bits (chevrons) like those indicated in FIGS. 1 and 2 are, for some purposes, more desirable and efficient than single servo-bits--for instance, they are "self-referencing", in the sense of needing no external "reference pulse train" for such purposes. For instance, a control servo pulse train for each track may be stored in "memory" and keyed to the track number and to a prescribed disk rpm. Those may be used as the "reference pulses" to be compared with the raw servo pulses, with any associated errors (lead-time or lag-time) computed with reference thereto.

The significance of the aforementioned dual-gap transducer array and the associated "adjacent orthogonal" alignment of data/servo bits and recording tracks will be evident. Such a "di-bit/di-gap" type "track-on-data" technique is contemplated in the described, and other related recording/servo positioning systems. Such systems will be better understood by consideration of the explanation indicated in FIG. 3B and described below as follows.

FIG. 3B:

An arrangement like that of FIG. 3, 3A is very schematically shown in FIG. 3B wherein similar data magnetic bits "dd" are obliquely aligned along the indicated track segment, with transverse singular "servo" bits "ch" similarly arranged at selected regular intervals along the track, but aligned orthogonal to data bits "dd", and laid across several of them. Here, (as above) it will be understood that a di-gap transducer arrangement will present two gaps, each to be uniquely parallel and aligned with bits from only one set (see gap g.sub.a for work-bits "dd", and gap g.sub.b for servo-bits "ch" in FIG. 3B). The "data output pulses" (when bits "dd" are sensed by g.sub.a) are represented in idealized fashion by pulse train S-A in prescribed chronological/spatial relation with the depiction of work-bits "dd". A related train of "centered" "servo output pulses" S-B is similarly chronological and spatially referenced to servo-bits "ch", (the output from gap g.sub.b). It will be understood that, when exactly "centered", gap g.sub.b detects successive servo-bits "ch" to produce the pulses S-B, peaking at the indicated times (t.sub.o , t.sub.o ', etc.) separated by prescribed normal clock interval, or frequency f.sub.o (reflecting the corresponding spacing and relative transition speed of the servo-bits relative to gap g.sub.b). But if the head is "shifted left", off-center, then a time-shifted pulse train S-B' will be generated; whereas a "shift-right" will generate pulse train S-B".

In light of the above explanation, workers will recognize that misregistration of the di-gap transducer assembly (particularly gap g.sub.b therein) to the left of the indicated translation direction (see directional arrow on the track FIG. 3B) will produce a train of clock pulses S-B' which will lead the normal "registration-train S-B" by a prescribed "error time" (-.DELTA.t.sub.i), the magnitude of which is proportional to the degree of (leftward) misregistration (note negative value of .DELTA.t.sub.i indicating "leftward error", i.e., a "leading relation to time t.sub.o); whereas a rightward misregistration is indicated by pulse train S-B", namely servo pulses which lag the normal pulse time t.sub.o by prescribed positive error-time (+.DELTA.t.sub.ii). As before, one may "center" the transducer simply by comparing the raw servo output [S-B' or S-B"] with a "reference pulse" train [S-B; e.g., stored in memory and issue in prescribed time-relation with the "index pulse"], and using the time-difference (.+-..DELTA.t) to control a conventional servo system (via feedback control, etc.).

It will be appreciated that a "di-bit/di-gap"; "track-on-data" arrangement and technique as described in the indicated and other related recording-servo positioning systems may be advantageously employed. Such arrangements will be seen as especially advantageous in conjunction with an array of "abutting" of data tracks wherein the work-bits and servo-bits are in orthogonal relation between adjacent tracks and among themselves along a given track.

The above description has been concerned with the manner in which a di-gap head assembly may be precisely positioned among a plurality of selectable abutting track positions using di-bit indicia along the tracks. As pointed out previously, in a conventional type of magnetic disk system to which the present invention may be applied one could employ a plurality of such head assemblies, each arranged to operate with a different sub-set of such tracks--whether provided on a disk or other record medium. It will be understood that the positioning of each such head assembly relative to its data zone may be provided in the same manner as described herein. It will also be understood that, in order to more efficiently employ space on the disk, it is possible to intermingle "work-bits" with orthogonal "position bits" along a track.

However, it will ordinarily be preferred to reserve certain pre-designated "track sectors" for the servo-bits as a means of maintaining the integrity of the servo-indicia inviolate. For instance, a certain amount of "bit-creep" is unavoidable in the course of dozens of cycles of erasing and rewriting work-bits--with the result that, unless an appropriate servo-sector is so reserved, work-bits can shift in position along a track until they eventually creep into the area of the servo-bits, and become confused therewith. (Unless, of course, the entire track is erased and rewritten, including all servo-bits, with each data update, however minor).

It will also be understood that di-gap heads according to the invention will be applied as generally known in the art. One suitable, preferred type of application is suggested by control system 200 very schematically shown in FIG. 5. System 200 is generally structured and adapted to control the output from such a pair of associated transducers (H.sub.a, H.sub.b mounted on a common head mount HM) and implement the associated head repositioning and centering. Details may be found in cited U.S. Ser. No. 807,155 cited above. Details of like implementation are well known to workers (e.g., see similar arrangements in U.S. Pat. No. 4,007,493 to Behr, et al.; U.S. Pat. No. 3,903,545 to Beecroft, et al.; U.S. Pat. No. 3,185,972 to Sippel and U.S. Pat. No. 3,686,649 to Behr, and in other patents cited above).

FIG. 8 illustrates one form of (single-track) "spiral recording" [e.g., as opposed to the conventional "concentric track" digital recording on magnetic record disks for computers as above described relative to FIG. 1, etc.]. This embodiment will be understood as carried out on a magnetic record disk D.sub.s with di-gap transducer means. That is, a single, continuous ["open-ended"] spiral track t of magnetic skew bits will be understood as laid down on disk D.sub.s by di-gap read/write head "hs". Track t may be understood as composed of connected one-revolution spiral segments or "laps" [such as tracks: t.sub.1, beginning at "start point" B, t.sub.2, t.sub.3, etc., through t.sub.n terminating at "end-mark" E] wherein adjacent tracks exhibit orthogonally-skewed bits, as illustrated. The tracks can, as aforementioned, be "abutted" to conserve space [see "abutting herringbone" pattern described above].

FIG. 8 is also exemplary of an "along-track" mode of gap alignment, as opposed to a "radial" alignment such as indicated in FIG. 8A (described below). Also, and preferably, here, some registration, or centering, di-bits (e.g., "V-shaped" pattern R.sub.m are also placed periodically along each "lap") to accommodate a "fine" servo control of head position whereby head "hs" can better follow the pitch of each track in its continuous spiral path as explained before [here assume a pitch of one-track-width W.sub.t, i.e., a gradual shifting of track radial location each revolution by distance W.sub.t ].

Thus, one might begin recording on initial track lap t.sub.1 at starting point B, along start axis SR.sub.s, and record some data bits [skewed, as pictured, with respect to the track axis] with one of the di-gaps of head "hs" as known in the art. Then, when lap t.sub.1 is completed, the array would automatically begin recording the next lap t.sub.2, switching to the other (transversely aligned) gap of head "hs"--this serving to reverse the direction of bit-skew and provide orthoganality of data bits between adjacent tracks. Similarly, one would switch back to the first gap at the beginning of the next lap, t.sub.3 ; then switch back to begin t.sub.4, etc., etc., concluding on the "end point" E at the end of the final, inner-most, lap t.sub.n.

The construction and operation of disk D.sub.s, of head "hs", and of associated actuator A.sub.s, etc., will be understood by workers as conventional [and will correspond to that of the prior discussed arrays] except as otherwise stated. Thus, transducer actuate means A.sub.s will be understood as adapted to reciprocate head "hs", on arm "as", as radially of disk D.sub.s as known in the art, so as to "follow" the pitch of a spiral track t. Workers will appreciate--as a feature of this combination--such an arrangement is especially apt for thus continually varying gap position (and track position) as a function of disk rotation--spiral recording is simply one example of such a mode. Other examples might be an eccentric circle, an ellipse, etc., as workers in the art will readily understand.

Workers will also appreciate how such an arrangement as this may be readily adapted for "track-on-data" centering of virtually any track pattern, even the conventional "concentric" track pattern [e.g., as used to automatically accommodate "run-out" etc.]. Workers will also perceive that such an arrangement may readily be optimally implemented using state-of-the-art accessory means such as a solid state "servo motor" pm [as described below], together with related control means; or such as a programmable actuator-microcomputer, or the mechanical analog thereof. Workers will also appreciate that such tracks may be laid down in either rotational direction; that is, where disk D.sub.s is rotated clockwise, or rotated counter-clockwise.

FIG. 8A indicates how the arrangement of FIG. 8 may be modified to include a second [or a third, etc.] such di-gap head: i.e., head hs-2', in addition to hs-1', mounted on actuator arm ass', as understood above. In addition to the characteristics of head "hs" in FIG. 8, this head arrangement will be seen as capable of accommodating simultaneous read/write operations on two or more tracks, (see FIG. 9). For instance, this will be understood as accelerating the data (input/output) rate, using parallel rate input/output data channels as known in the art. A "special case" of such a "radial" head alignment and related multi-track read/write mode of operation FIG. 9 uses two continuous independent interleaved spiral tracks. Workers will also perceive that, in the embodiment of FIG. 8A, one of the di-gap heads, hs-1', happens to be oppositely aligned [along the track direction] from its companion head hs-2', (though it could be similarly aligned instead). Such may be necessary to maintain the adjacent orthoganality between tracks in the "abutting herringbone" pattern preferred.

Preferably, the embodiment of FIG. 8 involves a centering [fine servo] of technique implemented in the aforedescribed "track-on-data" mode as opposed to other more conventional modes such as a continuous mechanical tracking system which is coupled to follow track pitch as a function of disk rotation [e.g., a high precision worm gear on other continuously-operating lead screw thrust array coupled to disk-rotating spindle]. Such mechanical arrangements have some undesirable limitations re their precision, their quickness of response, their simplicity, and their expense; also they are particularly difficult to "back-up", i.e., to through into reverse quickly and smoothly.

As discussed below, we prefer to use a suitable stepper motor coupled directly to the transducer arm [see arm "as" FIG. 8] to actuate the di-gap head(s). Such a motor is preferably modified to provide "steps" (translation increments) which are small enough to accommodate the selected track density or pitch [e.g., here, for 100 turns per inch, with a pitch of 0.020 inches we prefer to use a step motor adapted to provide about 18 steps per track width--thus normally moving the gaps about one mil for each approximate 20.degree. of disk revolution].

Of course, workers will appreciate that even with such an arrangement for "normally" advancing the head [radially of the record disk], we will prefer to modify this to control it in a "track-on-data" centering mode as mentioned. This will, of course, help to verify that the head is indeed centered "on-track", as well as better maintain a true centering control [e.g., as opposed to resorting to some indirect expedient that does not monitor actual track position, such as "Table-Lookup", mechanical gearing means or optical tracking of the disk-edge or the disk-rotating spindle, etc.--usually combined with "counting-in" from the disk edge; though these may be acceptable in a "low tpi" array]. Workers will appreciate how aptly the described "spiral recording with di-gaps" is combined with techniques for "centering-on-data".

Workers will also appreciate that recording frequency f.sub.r may be adjusted to better equalize inter-bit separation S.sub.b. That is, if one records along the outer-most track at a first frequency f.sub.1 (for maximizing R/W resolution with a given arrangement of equipment--e.g., 10 K-b/inch), he would reduce f.sub.r as recording proceeded radially-inward of the disk. Alternatively, one could of course, keep f.sub.r constant and surface velocity constant (at the head) as he proceeded inward by increasing spindle rpm, as he proceeded inward though this is more cumbersome.

FIG. 9 schematically depicts preferred multi-track spiral recording embodiments wherein a plurality of spiral recording tracks [two illustrated] are shown; for instance, spiral tracks T-A, T-B and associated dual recording head hs' in FIG. 9B. The arrangements in FIGS. 9A and 9B will be understood as constructed and operating in the manner of the arrangement of FIG. 8 except as otherwise here indicated--though FIG. 8 will be understood as depicting a single spiral, not multi-spirals.

Now, the single spiral in FIG. 8 may be expanded to a multi-spiral as indicated schematically for disk D'.sub.ss in FIG. 9A, where a plurality of spiral recording paths (three spirals shown) are laid down in parallel--preferably, in "herringbone" fashion, with an associated multi-gap head. Thus, first, second and third parallel spirals (T-a, T-b, T-c, respectively) will be understood as transduced by respective magnetic gaps g-a, g-b, g-c of head H.sub.h along respective track positions (e.g., see "starting positions" #1, #2, #3 at start axis SR'.sub.ss for spirals T-a, T-b, T-c respectively; also corresponding terminal segments with respective end marks emm, adjacent the center of the disk's recording zone). Of course, the common spiral "pitch" would normally be set to accommodate the space occupied by such a multi-gap head.

However, as workers are well aware, with the higher track densities and closer track spacings (e.g., "abutting herringbone") preferred today, it is becoming impossible to keep pace using available head-fabrication technology--e.g., no practical "in-line" head (i.e., with gaps set in-line at same spacing as tracks--e.g., as understood in FIG. 9A) can presently be found to accommodate such multi-spiral recording where the inter-track spacing is at, or close to, zero (abutting). But, according to a salient feature of this invention, we have found that an array of (oblique) transducer gaps may be so disposed on a head as to accommodate "abutting" spirals, yet--surprisingly--still use recording space quite efficiently. Such a "spaced-gap" head is indicated at hs' in FIG. 9B where the gaps g-a, g-b are so separated as to define a pair of associated recording spirals T-A, T-B (on rotating disk D'.sub.s) which are closely inter-laced" and use almost all of the recording area, yet without crossing or interfering with one another!

That is, illustrative magnetic recording disk D'.sub.s will be seen as rotatably mounted and otherwise arranged for spiral recording transduction, such as with illustrated head hs', and on which the pair of continuous, multi-revolution spiral recording paths T-A, T-B will be understood as recorded and read-back. As a principle feature of novelty these spiral tracks are "interleaved", being--as it were--"wound together" as a pair of similarly-involuted parallel spirals separated a constant distance ds and spiralling in to the center of disk D.sub.s from adjacent it's outer edge.

That is, a first, outer spiral T-A will be understood as beginning (or ending) adjacent start axis SR'.sub.s on the outermost disk track position (i.e., position #1 along axis SR'.sub.s is an imaginary circle concentric with disk center; and see start-mark indicia sm) and as spiraling inward from there. Spiral T-A defines an involute curve whose radial distance from disk center continually decreases according to a prescribed "pitch function" of its radial position, i.e., as the spiral moves about the disk center at a prescribed pitch. First spiral T-A terminates after a prescribed number of revolutions (not here indicated, but selectible according to chosen track-density and spacing, as understood in the art) close to the center of the disk [see innermost segment of turn n-3 and end marks em].

In like manner, the second, inner spiral T-B, begins on track-position #4 (see start marks sm along circle #4 where it intersects start axis SR'.sub.s) to spiral inward, in parallel with spiral T-A and kept a constant spacing ds therefrom (here a spacing of three track widths is preferred, according to a second related feature of novelty). Spiral T-B completes the same number of revolutions as T-A and similarly terminates adjacent disk center [along circle n at end-marks em]. Track positions #1 through #8, etc., and including positions n -4, n -3, n -2, n -1, and n will be understood as equidistant imaginary "reference-circles" as illustrated (and as in FIG. 9A).

According to a related feature, the two spiral tracks are kept separated by an appropriate multiple of track widths "tw" (here 3 tw, see below). Thus, at "phase I", tracks T-A and T-B begin their excursions, along track positions #1 and #4, respectively. Similarly, at the start of the second revolution, or "phase II", track T-A has shifted by a pitch of two track widths and now occupies track position #3 (along axis SR'.sub.s), while companion track T-B now occupies track position #6.

Likewise, during the third revolution, or "phase III", tracks T-A and T-B will cross the start axis SR'.sub.s along track positions #5 and #8, respectively [maintaining the constant pitch of two track widths and always separated by distance ds, as mentioned].

The spiral is terminated at end marks em as indicated. Thus, the final pass ("phase N") for inner track T-B crosses axis SR'.sub.s at position n -1 and ends along position "n" (1/2 revolution later), while the analogous pass for outer track T-A crosses axis SR'.sub.s along track position n -4 to terminate, 1/2 revolution later, along position n -3 at stop marks em. (Note that spiral T-B is understood to have been written in the prior revolution so as to cross SR'.sub.s at circle n -3, with spiral T-A crossing, the while, at position n -6.

Such a "dual-spiral" may be looked upon as consisting of a single spiral (e.g., T-B) drawn to define a two-track width (2 Tw) "pitch, and "followed" by a second spiral (e.g., T-A), drawn along the next outer track--except for its innermost revolution (cf. in FIG. 9B, the track beyond T-A in phase N--i.e., n -2/then n -1--is blank) and except for adding an extra revolution on the outside (i.e., while T-A "follows outside" the first revolution of T-B, or phase I, it also has an added turn three track-widths beyond--i.e., first turn of T-A along circle #1, then #2). Thus, an "abutting dual spiral herringbone" pattern is generated, except for track positions #2/3 and n -2/n -3 and n (each being approximately "1/2 blank").

Workers will, upon consideration of embodiments after FIG. 9, be surprised at how efficiently and smoothly two such continuous spiral tracks may be so interleaved without interference, and yet how efficiently the recording space is used.

Further, by comparison with a single spiral recording (e.g., as in FIG. 8), it will immediately become apparent that the recording mode is simplified. For instance, the bits along each track in FIG. 9B may be written at the same slant for all revolutions, whereas in the "single spiral" mode (FIG. 8), bit slant orientation must be reversed with each revolution (e.g., switching from one gap to another in a di-gap head--as with head hs in FIG. 8, or one of gaps hs-1', hs-2' in FIG. 8A as explained above). This will be understood as a considerable simplification, likely reducing operational complexity and cost.

The illustrative head hs' (with "spaced-gaps") suggested for use in such a dual-spiral recording mode will reflect this simplicity [e.g., as compared with h.sub.ss in FIG. 8A]. Thus, in FIG. 9B a pair of recording gaps h-a, h-b will be understood, as part of head hs', with the gaps slanted obliquely with respect to track axis and orthogonally with respect to one another. These are mounted in common upon a translation array (only mounting arm as' is shown, for simplicity's sake), with the gap being separated by a prescribed separation distance "dss"--here "dss" constitutes the "three-track-width" separation between tracks T-A, T-B (ds=dss). Arm as' will be understood as reciprocated back and forth at a prescribed pitch relative to the rotational speed of the spindle drive for disk DS' as known in the art, this being indicated, very schematically, by arm reciprocator means REC, coupled synchronizedly to spindle rotating means ROT.

Of course, single gaps are here shown for simplicity and convenience; but it will be understood that each may constitute a plurality of gaps aligned as desired. Thus, for example, the gap g-a will be understood as transducing (reading and writing) outer track T-A, while companion gap g-b will similarly transduce inner track T-B. [When head hs' is positioned appropriately over disk DS', as understood in the art].

In addition to the above mentioned advantage of using a single orientation gap to transduce (each) entire spiral track, certain other advantages will also be evident to those skilled in the art. For instance, such a pair of multi-spiral recordings, when used in conjunction with an associated multi-gap head, will be understood as capable of simultaneous, parallel input/output with increased speed, while yet maintaining perfect synchronism between gaps and associated signals.

Thus, virtually any number of spirals may be so interleaved and wound together. "Pitch" P may be defined in terms of the number of operating transducer-gaps, G i.e., P=nG.times.Tw track-widths (e.g., where G=2 as for FIG. 9B, P=2, 4, 6, etc., track-widths).

Similarly, "track-spacing" ds (or gap-spacing dss) may be defined as some multiple of G plus ONE: i.e., ds=(nG+1) Tw (e.g., where G=2, as for FIG. 9B, ds=3, 5, 7, etc., track-widths).

Also, it will be apparent that such multi-spiral recording is optimized when practised in an "abutting herringbone" pattern--even taking advantage of using LAMBDA (".LAMBDA." or "V") servo indicia where feasible.

It will be understood that the preferred embodiments described herein are only exemplary, and that the invention is capable of many modifications and variations in construction, arrangement and use without departing from the spirit of the invention. For example, other "oblique-gap" transducers could, in certain cases, be used for such dual spiral recording. Also, such multi-gap recording can be used to enhance stereo, quadraplex or like multi-channel recording--e.g., using three gaps in tandem, each transducing a respective one of three interleaved spiral tracks, with one head devoted to low f signals, one: high f, the third: medium f.

Further modifications of the invention are also possible. For example, the present invention is applicable for providing "spiral recording" with other forms of recording and/or reproducing systems, such as those in which data is recorded and reproduced optically.

The above examples of possible variations of the present invention are merely illustrative. Accordingly, the present invention is to be considered as including all possible modifications and variations coming within the scope of the invention as defined by the appended claims.