Method of writing information on a magnetic-recording carrier.

p0001The present invention relates to a mode of writing information on a magnetic recording medium. It is particularly applicable to magnetic disk memories.

p0002In the information processing systems, the use of magnetic disk memories is increasingly frequent because of their storage capacity and the relatively short time taken by the magnetic heads read / write access to a information contained in any point of the disks from the time they received the order to access this information.

p0003It is known that the magnetic disks are information in coded form on the concentric circular recording tracks whose width does not exceed a few hundredths of a millimeter and which are arranged on both sides.

p0004the tracks are identified by assigning a sequence number j, j being an integer ranging from 0 to N-1, N being the total number of recording tracks .We called address, the expression coded number of order j of a track.

p0005The most frequently used codes are binary codes.

p0006Magnetic disks are driven by an electric motor and a constant speed.

p0007In current practice, particularly in the case of memories that include only a limited number of discs (generally less than 4 or 5), the information is recorded on each of the faces of the discs in the following manner. Maximum space is reserved for recording data to be processed by the information processor to which these memories appartiennent.Un minimum space is reserved firstly to check the addresses of tracks and Moreover, registration information necessary for position control over the tracks of the magnetic head associated with this face. Will be designated later by the name of tracks location information, both the addresses of these, the position control information. So we can say that all the information recorded on one face of a disc, contains a subset of tracks of tracking information.

p0008Consider for simplicity, a single disc. Preferably each side of the disc is associated a single magnetic head read / write, also called magnetic transducer read / write.

p0009In current practice, as described in the patent application No. 76.09357 filed March 31, 1976 on behalf of Honeywell Bull Company under the title: "Write mode Address on a magnetic recording medium "the information contained on each side of the disc are preferably distributed on equal and adjacent circular sectors S_O, S₁, ...., S_i, ...., S_not. Usually, one face of the disc is divided into dozens of sectors (usually 40 to 50%).

p0010When the face of the magnetic disc associated with the magnetic head moves in front thereof, the sector S_O is read by the head before the S sector₁The S sector before the sector S₂ and so suite.On said while the S sector_O precedes sector S₁, The S sector₁ precedes sector S₂, The S sector_i precedes sector S_{i + 1} etc ......

p0011More generally, when considering both information I_k-1 and I_k that follow a similar track number j of said face, we say that the Ik-1 information above information I_k if read by the head before it or that the information I_k following the information I_k-1. The reasoning also applies to several adjacent information groups G_k and G_k-1.

p0012If each sector is divided into two unequal areas. The largest area includes the data to be processed by the information processor that owns the disk storage while the smallest area includes tracks location information. To simplify subsequently be designated under the name data to be processed, the data contained in the larger area. For each sector, the smallest area is divided into several areas called "reference areas" in number equal to that of tracks, each track being associated with a single area.

p0013It is recalled that the English word "bit" refers to both a binary digit 1 or 0 and any materialization of this figure is as magnetic recording, or as an analog electrical signal or logic, a logic signal that can take two values ​​called "logic zero" or "a logic" and an analog signal being defined as a signal whose voltage may vary continuously between two positive limit values ​​and / or negative. For simplicity, we will refer later as the "bit" any information or data recorded on the disc. In particular, the location information of the tracks will also be called "bit" tracking leads.

p0014It is known that, for recording a data pattern on a magnetic disk, is created on each track thereof a succession of small magnetic domains referred to as "elementary magnets" variable length distributed over the entire length of the track and having alternately magnetic inductions of the same module and of opposite sense of direction parallel to the disk surface. The number of elementary magnets of positive magnetic induction is equal to the number of elementary magnets of negative magnetic induction.

p0015In current practice, as described in the patent application No. 76.09357, it maps each "bit" of identifying tracks of any references area, only one change of direction of the magnetic induction named also change the direction of magnetization or magnetic transition that can have two different types, namely:<ul><li>- When the surface of the disk moves past the magnetic head and that it sees successively scroll an elementary magnet induction minus and an elementary magnet of positive induction, we say that the nature of the change in magnetization direction is positive, or although the magnetic transition is positive;</li><li>- When on the contrary, sees the head successively scroll an elementary magnet and induction plus an elementary induction minus magnet is said that the change in magnetization direction is negative in nature, or that the magnetic transition is negative.</li></ul>

p0016Recall that the address of a track comprises a number p of "bits", such as 2^p is greater than or equal to the number of tracks N

p0017Each reference area of ​​a sector S_., Associated with a sequence number of track j, comprises n cells, C1, C₂, C ....._k....... C_not, N being integer generally greater than p, each of which comprises at least one "bit" tracking tracks.

p0018The change of magnetization direction or the magnetic transition corresponding to each of these "bits", can occupy one of two predetermined positions within the cell, the value of the "bit" corresponding depending on the position of said change as described in the patent application No. 76.09357 above. Thus, if the magnetic transition, corresponding, for example, a "bit" address, occupies the predetermined position called the first position which is encountered the first time by the read head when it passes in front of the face of the magnetic disk which associated with it, this address bit is equal to O. If, conversely, the magnetic transition occupies the other of two predetermined positions, called the second position, the "bit" address is 1. A similar reasoning can be made to the "bits" position control.

p0019When the magnetic head encounters a sequence of magnetic transitions corresponding to a reference area, it delivers, for each transition an analog pulse which is converted into a logic pulse shaping circuits belonging to the disk drive to which belongs the magnetic disc, the beginning of the reference zone being indicated by a particular pulse. The logic pulses are sent to the read / write circuits of the disc memory.

p0020So that an analog pulse corresponding to a magnetic transition of a reference zone, be taken into consideration -that is to say, converted into a logic pulse - it is necessary that the amplitude of the analog pulse is exceeds a certain threshold or level, which in current practice, is relatively small and corresponds approximately to 25% of the maximum amplitude that can reach any analog signal output from the head. Determining the value of any "bit" Track Marking of the area is carried out as described in the French patent application filed on September 20, 1976 under No. 76.28169 the International Company for Computer CII- Honeywell Bull under the title: "Address reading process on a magnetic recording medium and apparatus for implementing" that is to say, identifying the position in time of the logic pulse corresponding said transition relative to the logical pulse indicating the start of the said reference zone.

p0021In conclusion, we see that any magnetic transition T_k corresponding to a "bit" Ik a reference area, corresponds to a logical pulse which occupies a position P_k marfaitement determined in time with respect to the particular pulse indicating the beginning of the zone.

p0022Be called spurious signal (an area), any signal delivered by the head when the area moves past it, which does not correspond to one of the transitions of a reference area, which is particularly the case for all no signal occupying said positions P_k. The appearance of such spurious signals can occur for various reasons, positional variation of the magnetic read head relative to the disc face associated with it, recording defect of the disk face, presence of dust between the side the disk and the magnetic head.

p0023The writing mode information within the reference areas of a magnetic disk according to the prior art has disadvantages, due to the fact that:<ul><li>- The scrolling speed of the information to the magnetic head varies, depending on whether this information is at the periphery of the disc or inside the drive (it decreases towards the center). This results in uncertainties in determining the position P_k pulses corresponding to T transitions_k a reference area and variations both in the length than in the amplitude of the same logic or analog impuisions.</li></ul>

p0024As a result, the probality for the read / write circuits of the disk memory take into account an interference signal is not negligible.

p0025It is known that the signals delivered by the magnetic head associated with the face of a disc, which corresponding pundent to tracking track information zone sent to a head positioning device above the aisque, which allows one hand to radially displace the head from one track to which it is initially in a track B which is to be read the information and secondly to maintain perfectly centered the magnetic head over the track B during time required for reading information therefrom. So that track B information to be read by the head as quickly as possible and with maximum accuracy, it is important that the time ue head excursion of the track A to + a track B is as short as possible, this head actually reaches above the track B and finally precision centering relative to this track is the highest possible.

p0026It is shown that to meet these conditions, all read signals corresponding to all transitions of a reference area must not contain any false signal. We see that this requirement is not met entirely by the writing mode according to the prior art.

p0027The present invention overcomes these drawbacks by replacing, to define each "bit" of a reference area, the simple magnetic transition corresponding thereto by a double magnetic transition, the first of which is of opposite sign to the second.

p0028This mode of writing information of the invention which eliminates any error in determining the value of "bit", is reliable and safe. It is easier to implement.

p0029According to the invention, the mode of writing information on a magnetic recording medium where the information written in binary code and carried by a plurality of tracks contain at least a subset of "bits" of identifying tracks recorded within reference field groups, each track being associated with at least one zone, such that each comprises a plurality of magnetic transitions, is characterized in that all "bit" of a reference area is defined by at least one double magnetic transition of which the first is of opposite sign to the second.

p0030In a preferred embodiment the write mode of the invention, the value of the "bit" of information is depending on the absence or presence of the double transition corresponding thereto.

p0031Other characteristics and advantages of the invention will appear from the following description given by way of nonlimiting example and with reference to the accompanying drawings:<ul><li>In these drawings:</li><li>- Figure 1 shows in a simplified diagram, how are written information on a magnetic recording medium such as a magnetic disc, Figure la being a sectional view taken at the level of a track, figure 1b a top view ;</li><li>- Figure 2 shows a preferred example of information distribution on a face of a magnetic disk;</li><li>- Figure 3 shows a mode of writing information in a reference area according to the prior art;</li><li>- Figure 4 is a block diagram showing the writing mode information within a reference region of a magnetic recording medium, Tel a magnetic disk according to the invention.</li><li>- Figure 5 illustrates the advantage of the information writing method according to the invention, based on the information writing mode according to the prior art;</li><li>- Figure 6 shows how the "bits" of a reference area, written following the write mode of the invention are divided into three groups, one group called preamble, a second component the address of the associated track in said zone, a third containing "bits" position servo.</li><li>- Figures 7, 8 and 9 respectively show preferred detailed embodiments of the first, second and third preceding groups.</li></ul>

p0032To better understand how the information is written reference areas of a magnetic recording medium according to the invention, it is helpful to do some reminders illustrated in Figures 1, 2 and 3 showing the one hand, how are written and spread the information on the surface of a magnetic recording medium which is preferably a magnetic disk (1 and 2), and secondly a write mode information within a reference area according to the prior art (Figure 3).

p0033Figure 1 ie representations and Ib show the form of a rectangle of serial number j track portion of a magnetic disk D.

p0034This magnetic disc D comprises a magnetic metal carrier MS on which is deposited a thin layer of magnetic material CM.

p0035It is recalled that for magnetizing a magnetic material is first subjected the latter to a magnetic field, created by a magnetic head to write / read, the intensity is sufficient for the material is saturated ie that the magnetic induction in the material reaches a limit value Bs when the intensity of the magnetic field H reaches a certain value Hs. then cancels the magnetic field. It then remains within the material a non-zero magnetic induction said remanent induction Br which depends on the magnetic material used.

p0036To write the information on each order number j track of the disk D is created by means of a magnetic head read / write T a plurality of elementary magnets Alj, A2j, A3J, a4j, a5j ,. ..etc.

p0037The magnetization axes FLJ to F5J that define the direction and sense of induction in elementary magnets Alj to a5j are parallel to SM medium and successively in opposite directions. Thus, the direction of the axis f 1 j is opposite to the direction of F2J axis, the direction of the axis F2J within the meaning of f3j axis and so on. The value of the magnetic induction within the elementary magnet is equal to (Br +) or (-Br). Thus, if the value of the induction in the elemental magnet is Alj (+ Br), the value of the induction in the elemental magnet A2j is (-Br), and so on. The length of the elementary magnets is variable.

p0038In Figure 2a, it is considered, rotating in the direction of the arrow F, the disc D, the useful recording surface is delimited by the dl and d2 circles. We define these discs n equal and adjacent circular sectors S_O, S₁,. S_i..S_not.

p0039As seen in Figure 2b, each sector S_i is divided into two parts SDO_i and SAD_i which are recorded respectively on the one hand, the "data to be processed" on the other hand the tracks of tracking information. The surface of the part SAD_i is much lower than the surface of the SDO part ..

p0040Figures 2c and 2d are an enlarged view of the portion SAD₁ If sectors included within the circle C.

p0041Each party SAD_i S. a sector is divided into N reference zones ZRP_iO ···^ZRP_ij···^ZRP_{i (n-1)}. To sim plify, shows only the first five zones ZRP_iO to ZRP_i4 which are symbolized by rectangles.

p0042The boundaries between different reference zones ZRP_ij Ax are circular magnetic axes. the tracks will of the magnetic recording disk D. We see that in each sector S_iThe serial number of track j, Ax axis. is associated with the reference zone ZRP_ij. AIN- whether to track 0, is associated with the reference zone ZRP_{iO '} to track 1 is associated with the reference zone ZRP_i1 And so on.

p0043In a write mode information within reference areas of a magnetic disk according to the prior art, (see Figure 3), each area ZRP_ij comprises a set of elementary cells of which the number is at least equal to the number of "bits" of identifying tracks that contains the area, each cell being associated with a "bit" tracking tracks.

p0044An exemplary embodiment of such a unit cell is given in Figure 3 where there is shown an elementary cell C_k a reference zone ZRP_ij. It was included in this figure the start of the area DZ consists of a first positive magnetic transition.

p0045Cell C_k a reference zone ZRP .. comprises two elementary magnets and hence a single magnetic transition which can occupy two predetermined positions within the cell, the value of the "bit" tracking tracks I_k corresponding to this magnetic transition depending on the position of information within the cell C_k.

p0046<ul><li>- If the magnetic transition occupied e the first predetermined position referred to as P_O, The "bit" I_k matching is zero;</li><li>- If the magnetic transition is second predetermined position, referred to as P₁, The "bit" I_k matching is 1.</li></ul>

p0047One can observe that, whatever the value of the "bit" I_k, The magnetic transition which corresponds always keep it the same kind for example positive as shown in Figure 3. It has been indicated in the same figure the magnetic transitions by a double line, the beginning of the zone by the magnetic transition DZ and the direction of the magnetic induction within each of the elementary magnets of the cell C_k.

p0048The writing mode information within a reference zone of a magnetic recording medium according to the invention is shown in Figure 4, where there is shown, as in Figure 3, a portion of a reference zone ZRP_ij, Namely the beginning of the area with the first magnetic transition DZ and an elementary cell one C_k the reference area comprising a plurality of elementary cells C₁C₂C₃... C_k... C_notThe number of cells being at least equal to the number of location information of the tracks must contain the area.

p0049According to the invention, while "bit" I_k a reference zone ZRP .. is defined by a double magnetic transition, the first magnetic transition T_1k being of opposite sign to the second magnetic transition T_2k. For example, the first transition T_1k is positive while the second transition is negative. The coding of "bits" of a zone is selected, for example, such that the "bit" I_k is equal to 1 when there is presence of a double magnetic transition, whereas it is zero when there is an absence thereof. To simplify later be designated under the Anglo-Saxon name "dibit", the absence or presence of a double magnetic transition. All C cells₁... C_k... C n have the same length L. When the "bit" I_k is equal to 1, the length of the portion of the cell C_k where the magnetic induction is positive is equal to the total length of the portion of the cell where the induction is negative. Thus, if the first magnetic transition T_1k is positive and the second T_2k If not, the length of the central elementary magnet of the cell C_k where the magnetic induction is positive, is equal to L, while the length of the two elementary magnets or the magnetic induction is negative, is equal to L. each magnetic transition is shown by a double line in Figure 4. It can be seen that, when the cell C_kcontains no double magnetic transition, magnetic flux density is uniform within said cell, for example negative in the embodiment of the write mode of the invention shown in Figure 4.

p00505a and 5b respectively represent the corresponding analogue and digital signals to a "bit" I_kwritten in the writing mode according to the prior art and according to the writing mode of the invention.

p0051Considering Figure 5a. At the same "bit" I_k a C cell_kwritten ZRP .. area following the write mode according to the prior art, can match various forms of analog signals output by the head T associated with the face of the disk that contains the "bit". At these analog signals corresponding digital signals, analog signals are converted into digital signals by forming electronic circuits as has been written above.

p0052We first assume the "bit" I_k recorded in a reference zone associated with a runway located at the periphery of the disc, the disc then scrolling with fast speed, before the head T. In this case, the analog signal corresponding to "bit" I_k\ Has an amplitude which can vary between a maximum value A_max and a minimum value A. , According to the provisions relative position of the head relative to the disc, the amplitude of the signal delivered by the head being maximum when the head is positioned exactly opposite the magnetic transition corresponding to "bit" I_k and a minimum distance from the disc, the amplitude of the signal delivered by the head being minimum when the head is located at a maximum distance of the disc and offset with respect to the magnetic transition.

p0053IARMAX either the analog signal delivered by the head corresponding to "bit" I_k and whose amplitude is maximum or the minimum IARMIN amplitude signal A. for that same "bit".

p0054When the I bit_k is recorded in an area ZRP .. associated with a track located within the disk, the scroll speed of the information is called slow and is lower than the speed of said high speed. In this case, the amplitude of the analog signal delivered by the head T varies between a maximum value_max and a minimum value_min, The amplitude signal_max is referred IALMAX while the corresponding minimum amplitude signal_min mé is dénom- IALMIN. It is seen that the amplitude a max IALMAX signal corresponds to the slow running speed and less than the amplitude A_max IARMAX the signal corresponds to a speed faster scrolling. It is the same for the amplitude a_min which is less than the amplitude A_min It is also seen that the duration of the IALMAX pulse is greater than the duration of the amplitude IARMAX. It is the same for the duration of IALMIN and IARMIN signals.

p0055The analog pulses are transformed into logic pulses by circuits thresholds (not shown) as follows. When the analog pulses have a voltage higher than a threshold TR, they are transformed into logic pulses. Thus, ILRMAX pulse in the time interval between the instants t_O and t₁ where its voltage is higher than TR. Similarly, IARMIN analog pulse is converted into a pulse ILRMIN between the instants t₂ and t₃ period of time during which the voltage is higher than TR. Similarly, IALMAX analog pulse is converted into a logic pulse ILLMAX between the instants t '_o and t '₁During which the IALMAX pulse is greater than TR voltage.

p0056As has been described above, the determination of the value of "bits" I_k is carried out by identifying the position in time of the pulse indicating the start of the zone and which corresponds to the magnetic transition DZ.

p0057Examination of Figure 5a leads to the conclusion that the logic pulse corresponding to the information I_k is detected at the instant t '_o or t_O according to the scroll speed information I_k recorded on the disk is slow or fast. Clearly, in these circumstances, that the determination of the value of the "bits" has for error.

p0058Consider an analog pulse IPA parasite whose voltage exceeds the threshold TR. Two cases are possible:<ul><li>- When IPA spurious pulse occurs outside the period where the voltage of the analog pulse corresponding to "bit" of information I_k is above the threshold TR, IPA interference pulse is transformed into a logical pulse IPL and is counted by the logic circuits to read and write of the memory disks to which belongs the disk D;</li><li>- When the one hand, the parasitic pulse IPA occurs within the period during which the voltage of the analog pulse corresponding to "bit" I_k TF is greater than the threshold and, on the other hand, is of opposite sign thereto, resulting in the existence of an analog signal, algebraic sum of the pulse IPA and said analog pulse, the voltage may being less than the threshold TR. As a result, the risk exists that there is no logic pulse corresponding to this signal, which means that the "bit" I_k may not be detected and taken into account by the read / write circuits. This then leads to errors, for example in determining the address of a track.</li></ul>

p0059Consider Figure 5b where the analog and digital signals are shown corresponding to a single "bit" I_k equal to one, written according to the write mode according to the invention that is constituted by a double magnetic transition.

p0060When it passes the magnetic head T, the latter delivers an analog signal which consists of two analog pulses of opposite sign whose amplitudes are equal and are a function of the speed of travel of the double transition before the head T, to a frame rate can match analog signal whose amplitude varies between a maximum amplitude a_max and a minimum amplitude A_min. The maximum amplitude of signal A_max DBARMAX is called when the minimum amplitude of signal A_min corresponding to a slow frame rate is called DBARMIN.

p0061Similarly to a slow frame rate ( "bit" I_k located inside of the disc), is an analog signal whose amplitude may vary between a maximum amplitude and a minimum amplitude amax .. The amplitude signal is referred DBALMAX, while the amplitude signal_min is called DBALMIN.

p0062Dual analog pulses corresponding to transitions doubles corresponding to the "bits" I_k C cells_k a reference zone ZRP_ij are transformed into logic pulses by circuits thresholds. TR is the threshold.

p0063When the voltage of the analog signal is greater DBARMAX_- TR périeure the threshold or at the time t4, the corresponding logic pulse DBLRMAX becomes equal to a logic. This pulse falls to logic zero at time t5 in which the voltage of the dual analog pulse DBARMAX becomes zero by moving from positive to negative. Similarly, the logic pulse DBLLMAX is equal to logic 1 between t'4 moments in which the voltage of the analog pulse DBALMAX TR exceeds the threshold and the instant t5 when this tension becomes zero. Similarly, DBARMIN transformed into logic pulse DBLRMIN between t6 in which the voltage of this DBARMIN signal exceeds the threshold TR and time t7 for which it passes through zero, (moving from positive to a negative value) as can be seen in Figure 5b.

p0064It is thus seen that the duration of logic pulses corresponding to the bit I_k has a minimum T_at = (T7 - t6) perfectly determined.

p0065We also see that the zero crossing as the DBALMAX impulse of DBARMAX pulse occurs at time t5, which remains the same as the information I_k is located in the periphery or inside of the disk; in other words, this means that, regardless of the reference zone ZRP .. the same sector S_iThe time that elapses between when we mark the beginning of the DZ area and the instant t5 when the logic pulse corresponding to the kth "bit" I_k said area falls to logic zero, that is to say at time t5 is the same.

p0066This leads to the following consequences:<ul><li>Detecting the presence or absence of a double transition corresponding to the bit I_k by identifying the fallout zero logic that corresponds to "dibit". (It is also said: detecting the "dibit" corresponding to a bit I_k). In other words, this means that, when it is detected the presence or absence of a logical pulse by the drop to logical zero of the pulse, simultaneously determines the value of this information (equal to one if presence and zero if there is no pulse, so drop-off to logical zero following the coding chosen for writing the "bits" shown in fig. 4).</li><li>We know that tracking the fallout at logic zero pulse by digital electronic circuits used in current practice is extremely accurate.</li><li>Furthermore, it considers a spurious pulse and analog IPA whose voltage exceeds the threshold TR. This analog pulse is converted by the threshold circuits in a logic pulse pulse width IPL T '. If as is the case in current practice, the duration T 'of the parasitic pulse is less than the duration T_at, The read / write circuits of the disc memory do not take into account the parasitic pulse.</li></ul>

p0067The writing mode of the invention thus provides:<ul><li>- On the one hand, accurate detection of the slopes location information, which greatly reduces the risk of errors in the determination of the value of bits, based on the write mode information according to the prior art and ,</li><li>- Secondly, to virtually eliminate any consideration of almost all the glitches that can occur when a reference zone ZRP_ij moves past the magnetic head T.</li></ul>

p0068In a preferred embodiment of the writing mode information within a reference zone of a magnetic disk according to the invention, the reference zone ZRP .. is divided into three separate parts from beginning of the DZ zone, a part called preamble part PPA, DBP part comprising the address of the order of track number j which is associated with said reference zone and a third part PLUPs comprising the servo information of position of the head over the disk; (Also called fine position information).

p0069This mode of distribution of information within a reference zone ZRP .. can increase the accuracy of their detection, avoiding that in the latter, the signals corresponding to one type of information (address for example), not disrupt the signals corresponding to another type (f position information_i- Not, for example) which is the case when information of one type precedes a second type of information, itself prior information of a third type, and so on as is frequently done in practice common.

p0070The preamble part PPA contains a number of "dibits", operation signals corresponding to these dibits by the read / write circuits of the disk drive to determine the gain of amplifiers of these so that the precision circuits reading addresses and fine position information is as large as possible. In a preferred embodiment of the invention, the preamble portion contains 12 PPP "dibits" identiques'correspondant to bits equal to 1. This preferred embodiment of the preamble part PPA is shown in Figure 7 where one has included the positive magnetic transitions by a line provided with an arrow pointing upwards and negative magnetic transitions by a line with an arrow pointing down and to simplify the drawing.

p0071In one embodiment of the invention (see Figure 6) the PAD portion that includes the addresses consists of twelve cells C^I_O C '₁₁ each containing one "dibit". One of the cells, for example the first cell C '_O contains a "dibit" which corresponds to a "bit" information indicating the parity of the track. The "dibit" contained in the eleven other cells C '₁ C '₁₁ corre^ptooth on- the "bits" of the address of the track associated with the reference zone ZRP .. containing said PAD portion. Denoting by k the number of "bits" of the address of a track, it is known that it is such that 2^k is greater than or equal to the number N of recording tracks. Thus, if k = 11, the maximum number of tracks that may be a 11 "bits" binary code is equal to 2 0₄₈ (2 048 = 2¹¹). In the embodiment described herein, "dibit" that correspond to the significant bits of the address precede "dibit" corresponding to low weight. Thus the cells containing the "dibit" corresponding to the high weights are located on the left of Figures 6 and 8, cells containing "dibit" corresponding to low weight being on the right side of these figures. As a result, the cell C '₁ contains the "dibit" corresponding to the most significant address of then the cell C '₁₁ contains the "dibit" corresponding to the lower weight.

p0072Consider Figure 8 represents two PAD parts of two adjacent reference areas namely areas _ZRPi124 and ZRP_I125The addresses of the two tracks corresponding to these two areas to be written in the writing mode of the invention, preferably in a reflected binary code or code "GRAY". A description of this code is given for example in the book of H. SOUBIES-CAMY published by Dunod in 1961 on pages 253 and 254.

p0073To simplify the figure 8, it did not include, for each of the two zones ZRP_I124 and Z^RP_I125 Cell C '_O containing the "dibit" indicating the parity of the address. DB will denote₁ DB₁₁ the "dibit" contained respectively in each cell C '₁ C '₁₁.

p0074<ul><li>8a gives expression in code "GRAY" numbers 124 and 125.</li><li>Figure 8b shows how the addresses of the tracks 124 and 125 are written on the magnetic disk, "GRAY" code within the reference zones ZRP_I124 and ZRP_I125.</li><li>8c shows the read signal of written addresses in both zones ZRP_I124 and ^ZRP_I125 by the read head and / or T writing, it is assumed perfectly centered on the axis Ax_I124 the track address 124, which is the magnetic axis forming the border between the two aforementioned areas. It may be said in other words, the head T is disposed astride both zones.</li></ul>

p0075As can be seen in Figure 8a, the characterization risti^qessential eu code "GRAY" lies in the fact that two successive addresses are distinguished by the change of a single "bit" therebetween. And the 124 and 125 addresses written in code "GRAY" differ in the last "bit", 0 for track 124 and equal to 1 for the track 125.

p0076It has been assumed in Figure 8b, the mode of representation of "di-bits" is identical to that of Figure 7, the absence of double magnetic transition in cells C '₁ C '₁₁ corresponding to "bits" to address equal to 0, the presence of a double transition corresponding to a "bit" address equal to 1. It was also shown in Figure 8b the sign of the magnetic induction in each cell C '₁ and C '₁₁ and said the value of the "bit" for each "dibit" DB₁DB₁₁ of each of the addresses of the tracks 124 and 125.

p0077It is seen that the cells C '₅ and C '₁₀ the two areas ^ZRP_I124 and ^ZRP_I125 contain a double transition _my- g_notethics and the cell C '₁₁ of ZRP area_I125None of the other cells of the above two zones containing double magnetic transition.

p0078As can be seen in Figure 8c, the signal delivered by the head T is constituted by the following analog pulses S₅₊- S_5-; S₁₀₊ - S_10- ; S₁₁₊ S_11-. S Pulse₅₊ and S_5- correspond to the double magnetic transition cell C '₅ the two zones ZRP_I124 and ZRP_I125, The signals S₁₀₊ and S_10- corresponding to the double transition of cells C '₁₀ the same areas and the analog signals S₁₁₊ and S_11- corresponding to the double magnetic transition of the cell C '₁₁ of ZRP area_I125. The analog signals S₅₊, S₁₀₊ and S₁₁₊ are positive while the signals S_5-, S₁₀- And S_11- are negative. If the amplitudes of the signals S₅₊ and S₁₀₊^S_5- and S_10- are respectively equal to (+ A) and (-A), (the amplitude of the head T issued read signal being assumed maximum) it is seen that the amplitudes of the analog signals S₁₁₊ and S_11- are respectively equal to (+ A / 2) and (-A / 2). Clearly, for the cells C '₁ C '₄ and C '₆ C '₉The corresponding signal from the head T is zero.

p0079Consider Figure 9a represents PPOS two parts of two adjacent reference zones ZRP_{i (j-1)}^sup- asked odd and ZRP assumed .. pair. Assume that in the example described here, both parties PPOS-called reference area contains twelve cells C "₁ -C "₁₂. It was also shown in the same figure 9a the last cell C '₁₁ both parties PAD same zones ZRP_{i (j-1)} ZRP and ...

p0080We see that the odd order of C cells "₁, C '₃, C '₅, C '₇, C '₉, C '₁₁ the reference area corresponding to a track pair ZRP .. contain "dibits" corresponding to "bit" fine position information equal to 1. It is seen, on the other hand, in a portion PLUPs reference area corresponding to an odd-numbered track, the odd-cells C "-C"₁₁ contain "dibits" corresponding to bits equal to 1 fine position information, while the pair C-cells "₂ -C "₁₂ contain "dibits" corresponding to "bit" fine position information equal to 0.

p0081In conclusion, we can say that, for both pairs of tracks for odd tracks, the PPOS part contains a series of twelve cells characterized by the fact that there are alternate presence and absence of magnetic transition for cells successive. One can also say that the writing mode information in the PLUPs part is identical, whether it is an even or odd track, the information being simply shifted one cell to another; thus, the cell C '_l a pair of track order number (j-1) or (j + 1) contains the cell C '₂ PLUPs of the portion of the pair track of serial number j containing a double transition, the cell C '₂ the neighboring odd track of the sequence number (j-1) or (j + 1) not containing and so on. Figure 9b shows two types of analog signals from the reading head and / or T writing, depending on the position it occupies relative to the magnetic axis Ax_{i (j-1)} the serial number of track (j-1).

p0082When the head T is perfectly centered on the axis Ax_{i (j-1)}, The analog signal delivered by the latter is SA. not

p0083When the position of the head T is substantially as two thirds thereof are situated opposite the PLUPs part of the reference zone ZRP_ijThe other third of the head is located opposite the PLUPs part of the reference zone ZRP_{i (j-1)}The analog signal is issued SA_d (Indicated by a broken line in Figure 9a).

p0084As can be seen in the same figure, the analog signal SA_not is a mean zero voltage signal whose voltage varies between a maximum positive value (+ A / 2) and a negative maximum value (-A / 2). We see that the SA signal_not is substantially sinusoidal.

p0085Consider the signal SA_d. We see that the voltage is between the positive maximum value (A +_b) And a negative minimum value (-A) when the head T is located above the odd-numbered cells ^C"₁, C '₃... C "₁₁ and between a positive maximum value (A +_h) And a negative maximum value (-A_h) When the head T is located above of pair-cells ^C"₂, C '₄, C '₆.. C "₁₂.

p0086It is shown that such an arrangement of "bits" of fine position within the PLUPs part of an area, allows, during playback thereof, of almost completely avoiding interference phenomena between the information signals from the two adjacent reference areas corresponding to order number of tracks j and (j-1) on the one hand, j and (j + 1) on the other.