JPH0636223A - Four megabyte flexible disk apparatus - Google Patents

Abstract

PURPOSE:To obtain a magnetic head for 4-MB FDD use at low costs by a method wherein a supermagnetic force generated in a recording and reproduction magnetic circuit in the recording of data is controlled so as to be changed by its direction. CONSTITUTION:Even when data which records a magnetization pattern recorded on a medium by a magnetic interference is a single-cycle pattern, an output obtained by reproducing it becomes asymmetric data. As a result, the margin of an FDD is lowered when the data is reproduced from the medium. Consequently, a supermagnetic force as the product of a recording current flowing in a first recording and reproduction coil 7 by a first recording current driver 20 and the number of turns of the coil 7 and a supermagnetic force as the product of a recording current flowing in a second recording and reproduction coil 7 by a second recording current driver 21 and the number of turns of the second recording and reproduction coil 7 are adjusted respectively so that they become the same magnitude even when their direction is the same as a magnetic field generated in an erasing gap 5 as the result of a magnetic interference with an erasing magnetic flux and even when the magnitude of a magnetic field generated in a recording and reproduction gap 4 is different. As a result, the symmetry of the magnetization pattern recorded on the medium becomes excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a 3.5-inch flexible disk device, that is, a 4-megabyte flexible disk device (4MBFDD).

[0002]

2. Description of the Related Art As a conventional device, a 2-megabyte flexible disk device (2MBFDD) will be described below as an example. FIG. 10 is a perspective view showing a configuration of a magnetic head device mounted on a conventional 2MB FDD, FIG.
FIG. 12 is an enlarged view showing the configuration of the gap portion as seen from the medium sliding surface in the magnetic head device of FIG. 10, and FIG. 12 is a perspective view showing the configuration of the magnetic head device mounted on another example 2MBFDD, FIG. 13 is an enlarged view showing the configuration of the gap portion viewed from the medium sliding surface in the magnetic head device of FIG. 12, and FIG. 14 is a diagram showing a magnetization pattern on the medium recorded by the conventional magnetic head device.

In the magnetic head device shown in FIG. 10, reference numeral 1 is a first magnetic core, and a gap forming joint surface is formed on both surfaces thereof. In the magnetic head device shown in FIG. 12, the first magnetic core 1 is composed of a non-magnetic separator 1c, a magnetic core 1a which composes a recording / reproducing magnetic circuit and a magnetic core 1b which composes an erasing magnetic circuit. There is. 2 is a second magnetic core, 3 is a third magnetic core, 6a and 6b are back cores, and 6c is a back core 6a.
And 6b are non-magnetic glass or air for preventing magnetic interference.

In the magnetic head device shown in FIG. 12, a recording / reproducing magnetic circuit is constituted by the second magnetic core 2, the magnetic core 1a and the back core 6a, and the third magnetic core 3, the magnetic core 1b and the back core 6b. The erase magnetic circuit is composed of. 4 is a recording / reproducing gap, 4a is a recording / reproducing gap 4
Is the gap length of. Reference numeral 5 is an erase gap. A read / write coil 7 is wound around the second magnetic core 2. 7
Reference numerals a and 7c are recording / reproducing coil terminals, and 7b is a recording / reproducing coil center tap. Reference numeral 8 is an erasing coil, which is wound around the third magnetic core 3. 8a and 8b are erase coil terminals. Reference numeral 9 is a mold glass for joining the first magnetic core 1 or the magnetic core 1a and the second magnetic core 2. Reference numeral 10 is a mold glass for joining the first magnetic core 1 or the magnetic core 1b and the third magnetic core 3 together. Reference numeral 11 is a magnetization pattern recorded on the medium by a conventional magnetic head device. When an erase current flows by the tunnel erase method, a DC erase area 12 shown in FIG. 14 is shown on the medium.

FIG. 15 is a timing chart showing the operating principle of the recording circuit of the magnetic head device mounted on the conventional 2 MB FDD and a diagram showing the reproduction output waveform of the magnetic head device. In the figure, λ is a recording / reproducing wavelength (wavelength of the magnetization pattern).

Next, the operation of the conventional magnetic head device will be described. Flexible disk (F
When recording data in D), the recording current shown in FIG. 15 is caused to flow through the recording / reproducing coil 7 of the magnetic head device shown in FIG. 10, and the magnetic field generated by the recording current is concentrated in the recording / reproducing gap 4. , The FD that contacts and slides with the magnetic head layer is magnetized at a relative speed v, and the magnetization pattern shown in FIG. 15 is recorded as data in the FD by reversing the magnetic field by positive / negative reversal of the recording current. When reproducing the data recorded in the FD, the recording / reproducing gap 4 shown in FIG. 10 moves in the magnetization reversal region of the magnetization pattern recorded on the FD at a relative speed v with respect to the FD to obtain a reproduction output. It is a thing.

The recording / reproducing gap 4 of the magnetic head device mounted on the 2 MB FDD performs two operations in the same gap without using separate gaps for recording and reproducing data. In order to increase the reproduction output, with respect to the recording / reproducing gap 4, a recording / reproducing gap length 4a and a magnetomotive force for obtaining a recording magnetic field that magnetizes the FD to a saturation magnetization region are necessary from the viewpoint of recording operation. The recording / reproducing gap length 4a is required so that the transition length of the above recording magnetization reversal becomes small and the recording demagnetization effect becomes small. From the viewpoint of reproducing operation, when the wavelength of the magnetization pattern recorded in the FD is λ, the output loss Lg during reproducing is Lg.
Is expressed by the following formula 1, and the reproduction output e is expressed by the following formula 2, the higher the reproduction output is obtained as the recording / reproducing gap length 4a is smaller than the wavelength λ of the magnetization pattern. Lg = 20log {sin (πg / λ) / (πg / λ)} [db] ··· Equation 1 e∝v · φ · η / g ····· Equation 2 e: Reproduction output v: Relative speed of FD and recording / reproducing gap φ: Magnetization amount of magnetization pattern recorded in FD η: Reproducing efficiency of magnetic head device g: Recording / reproducing gap length

In the above-mentioned conventional 2MB FDD, when data is updated, an overwrite erasing method in which the data is directly overlaid on the old data is adopted. In order to increase the overwrite erasing rate, recording / reproduction is performed. Gap length 4
a must be increased, and the wavelength for recording / reproducing is 2.92 μm or more and 19.84 μm or less, and has a track density of 5.3 tracks / mm, and MFM (modi
fied frequency modulatio
n) It has a maximum recording density of 15,916 magnetic flux reversal / rad depending on the recording method. The recording / reproducing gap length 4 of the magnetic head device mounted on such a conventional 2 MB FDD
a was manufactured in the range of 0.8 ± 0.2 μm.

In addition, the recording current shown in FIG.
The recording / reproducing coil center tap 7b and the recording / reproducing coil terminal 7a and the recording / reproducing coil center tap 7b shown in FIG. It is when the write gate shown is in the "L" state. At this time, the erase gate is in the "L" state after a short delay time, and the erase current also flows from the erase coil terminal 8a shown in FIG. 10 to the erase coil terminal 8b (or 8b to 8a) at the same time.

In the structure of the conventional magnetic head device shown in FIG. 12, the nonmagnetic separator 1c is provided so that the magnetic fields created by the recording current and the erasing current, which simultaneously flow as described above, do not interfere with each other. In addition, the non-magnetic separator 1c
In reproducing, the erase gap 5 shown in FIG. 13 is off-tracked and applied to the magnetization pattern 11 of the data on the FD shown in FIG. 14, the data is reproduced, and its magnetic flux becomes
Crosstalk to the second magnetic core 2 shown in FIG. 2 is prevented. However, even if the conventional magnetic head device without the non-magnetic separator 1c shown in FIG.
In the FDD, since the recording / reproducing gap length 4a is wide, in actual use, it does not matter so much about mutual interference between the magnetic fields created by the recording current and the erasing current during recording and the above-mentioned crosstalk during reproduction. .

In the conventional magnetic head device shown in FIG. 10 or 12, a back core used to close the magnetic circuit formed by the second magnetic core 2 and the magnetic circuit formed by the third magnetic core 3, respectively. 6a and 6b are adhered to the first magnetic core 1, the second magnetic core 2 and the third magnetic core 3 in the same plane. And the back core 6
Nonmagnetic glass or air is interposed between a and 6b, so that magnetic interference does not occur between the back cores 6a and 6b.

[0012]

The conventional 2 MB described above
Since the magnetic head device mounted on the FDD and the recording / reproducing circuit thereof are configured as described above, the maximum recording density by the MFM recording method is 15,916 magnetic flux reversal / ra.
and the unformatted storage capacity was 2 megabytes. Here, the maximum recording density is 31,832.
In order to set the magnetic flux reversal / rad, the unformatted storage capacity to 4 megabytes, and to secure the backward compatibility characteristic, the recording / reproducing gap length 4a of the above-described conventional magnetic head device is reduced to narrow the gap. It is necessary to make the device highly efficient.

Therefore, in order to improve the efficiency of the magnetic head device as described above, it is necessary not to provide the non-magnetic separator 1c in the structure of the first magnetic core 1 shown in FIG. . However, the first magnetic core 1
In the case where the non-magnetic separator 1c is not provided as the above, the influence of the magnetic interference between the recording / reproducing magnetic circuit and the erasing magnetic circuit in the magnetic head device becomes a problem. It was necessary to prevent the recording / playback from being affected. As a result, there is a problem in that it is extremely difficult to realize a 4 MB FDD that secures the backward compatibility characteristics and enables recording / reproducing with an unformatted storage capacity of 4 MB by the MFM recording method.

The present invention has been made to solve the above-mentioned problems, and assures backward compatibility characteristics and enables recording / reproducing with an unformatted storage capacity of 4 megabytes according to the MFM recording method. Aim to get.

[0015]

4 MB relating to the present invention
The FDD is a preceding erasing method and is equipped with a magnetic head device having a configuration in which a non-magnetic separator that is a magnetic separation layer does not exist in the first magnetic core, and is generated in a recording / reproducing magnetic circuit at the time of recording data. The magnetomotive force is controlled so as to change depending on the direction.

[0016]

In the 4 MB FDD of the present invention, a magnetic head device having a structure in which the non-magnetic separator is not present in the first magnetic core is used, and the magnetomotive force generated in the recording / reproducing magnetic circuit is controlled so as to be changed depending on the direction. Is the first
Of the magnetic core at the time of recording the data due to the absence of the non-magnetic separator in the magnetic core, the magnetization pattern of the recorded medium has good symmetry, and the magnetic head device, or other It is possible to improve the margin when this medium is reproduced by using the above device.

[0017]

【Example】

Example 1. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted on a 4 MB FDD which is Embodiment 1 of the present invention, and FIG. 2 is a gap portion viewed from a medium sliding surface in the magnetic head device of FIG. FIG. 3 is an enlarged view showing the configuration, and FIG.
FIG. 6 is a diagram showing a magnetization pattern on a medium recorded by the magnetic head device of FIG.

In the magnetic head device shown in FIG. 1,
Reference numeral 1 is a first magnetic core having a structure in which there is no non-magnetic separator for magnetic separation, and a gap type joint surface is formed on both surfaces thereof. Since the first magnetic core 1 does not have a non-magnetic separator, the magnetic resistance of the first magnetic core 1 is lower than that of the non-magnetic separator, which has the effect of increasing the efficiency of the magnetic circuit. is there.

Reference numeral 2 is a second magnetic core, 3 is a third magnetic core, and 6a and 6b are back cores. Recording and reproduction are performed by the second magnetic core 2, the first magnetic core 1 and the back core 6a. A magnetic circuit is formed, and a third magnetic core 3 and a first magnetic core 1 are formed.
And the back core 6b constitute an erasing magnetic circuit. Reference numeral 4 is a recording / reproducing gap, and 4a is a gap length of the recording / reproducing gap 4. Reference numeral 5 is an erase gap.

A read / write coil 7 is wound around the second magnetic core 2. Reference numerals 7a and 7c are recording / reproducing coil terminals, and 7b is a recording / reproducing coil center tap. At this time, the first recording / reproducing coil is between the recording / reproducing coil terminal 7a and the recording / reproducing coil center tap 7b, and the second recording / reproducing coil is between the recording / reproducing coil center tap 7b and the recording / reproducing coil terminal 7c. Reference numeral 8 is an erasing coil, which is wound around the third magnetic core 3. 8a and 8b are erase coil terminals. Reference numeral 9 is a mold glass for joining the first magnetic core 1 and the second magnetic core 2 and 10 is a mold glass for joining the first magnetic core 1 and the third magnetic core 3.

Numeral 20 is a first recording current driver for supplying a recording current to the first recording / reproducing coil, one end of which is connected to the recording / reproducing coil terminal 7a and the other end is grounded. Reference numeral 21 denotes a second recording current driver for supplying a recording current to the second recording / reproducing coil, one end of which is connected to the recording / reproducing coil terminal 7c and the other end is grounded. The recording / reproducing coil center tap 7b, which is the other end of each recording / reproducing coil terminal 7a, 7c, is connected to a power source as a common terminal. An erase current driver 22 has one end connected to the erase coil terminal 8a and the other end grounded. The erasing coil terminal 8b is connected to the power supply. Reference numeral 11 denotes a magnetization pattern recorded on the medium by the magnetic head device of the present invention. When an erasing current flows by the preceding erasing method, the DC erasing area 12 shown in FIG. 3 is shown on the medium.

FIG. 4 is a diagram for explaining that the amount of recording magnetization is increased by enlarging the recording / reproducing gap length in the magnetic head device of FIG. 1, and FIG. 5 is recording / reproducing with the conventional magnetic head device. It is a figure which shows the reproduction | regeneration output waveform at the time.

Next, the operation of the magnetic head device according to the first embodiment of the present invention shown in FIG. 1 will be described. The basic operation of the magnetic head device according to the first embodiment of the present invention is as follows.
Since it is the same as the above-described conventional magnetic head device, detailed description thereof will be omitted. In the 4 MB FDD, the minimum wavelength for recording / reproducing by the magnetic head device mounted therein is 1.46 μm, which corresponds to recording / reproducing “00 (h)” on the side 1 of the track 79. 4M
In order to record / reproduce the above wavelengths in BFDD without any practical problems, there is an optimum recording / reproducing gap length 4a in the magnetic head device, but from the viewpoint of reproducing operation, the wavelength of the magnetization pattern recorded on the medium. Where λ is λ, the output loss Lg at the time of reproduction is expressed by the above-mentioned formula 1 and the reproduction output e is expressed by the above-mentioned formula 2, so that the smaller the recording / reproducing gap length 4a is, the smaller the wavelength λ of the magnetization pattern is. High playback output can be obtained.

Since the data recorded by the 4MB FDD is also reproduced by another FDD, in order to increase the output when the other FDD reproduces the above-mentioned data, the medium (F
It is necessary to increase the magnetization amount φ of the magnetization pattern recorded in D), and this can be achieved by increasing the recording / reproducing gap length 4a of the magnetic head device. This relationship is clearly shown in FIG. Δ in FIG. 4 represents the thickness of the magnetic layer of the medium. As the recording / reproducing gap length 4a increases under the condition that the magnetomotive force is constant, the magnetization amount indicated by the arrow in FIG. Has been expanded in the direction. At this time, the value of φ becomes large.

As described above, the recording / reproducing gap length 4a of the magnetic head device mounted on the 4MB FDD does not match the appropriate gap length when recording data. Increasing the reproducing efficiency η of the magnetic head device with the above-described configuration of the magnetic head device means that the recording / reproducing gap length g can be increased in order to obtain the same reproducing output e in the above equation (2). By adopting the structure of this magnetic head device, the recording / reproducing gap length 4a of the magnetic head device according to the present invention is 0.45 μm or more and 0.55 μm.
Below, the reproduction output e is set to a value that causes no practical problem.

In the magnetic head device according to the present invention of the preceding erasing method shown in FIG. 1, the first magnetic core 1 is used.
Since the non-magnetic separator does not exist in the FDD magnetic head device of the FDD in which the recording current and the erasing current simultaneously flow in the magnetic circuit at the time of recording the data, the recording magnetic flux flowing in the second magnetic core 2 and the third magnetic field The erase magnetic flux flowing through the core 3 causes magnetic interference.

The magnetization pattern recorded on the medium by such magnetic interference is reproduced and output as shown in FIG. 5 when reproducing the recorded data even if the recorded data has a single cycle pattern. Waveform half periods t ₁ and t ₂ are t ₁ ≠
t _2, and the order thereof, output becomes asymmetrical data reproduced. As a result, the margin of FDD when data is reproduced from the medium is reduced.

Therefore, in the present invention, the magnetomotive force which is the product of the recording current applied to the first recording / reproducing coil by the first recording current driver 20 shown in FIG. 1 and the number of turns of the first recording / reproducing coil, The second recording current driver 21 adjusts the magnetomotive force, which is the product of the recording current flowing through the second recording / reproducing coil and the number of turns of the second recording / reproducing coil,
As a result of the magnetic interference with the erasing magnetic flux, the magnetic field generated in the erasing gap 5 has the same direction, and the magnetic field generated in the recording / reproducing gap 4 has the same direction. As a result, the magnetization pattern recorded on the medium has good symmetry.

Example 2. FIG. 6 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted on a 4 MB FDD which is Embodiment 2 of the present invention. Embodiment 2 of the present invention
Compared with the magnetic head device according to the first embodiment of the present invention described above, the number of windings between the recording / reproducing coil terminal 7a which is the first recording / reproducing coil and the recording / reproducing coil center tap 7b, and the second magnetic head device The number of turns between the recording / reproducing coil center tap 7b which is the recording / reproducing coil and the recording / reproducing coil terminal 7c is different. Further, in FIG.
Is a current source that determines the magnitude of the recording current, 24 is a switch for connecting the first recording / reproducing coil with the current source 23, 2
Reference numeral 5 is a switch for connecting the second recording / reproducing coil to the current source 23. Here, the current source 23 and each switch 2
Nos. 4 and 25 are incorporated in a head IC which is usually commercially available.

When data is recorded on the medium using the magnetic head device and the recording circuit (recording current driver circuit) configured as shown in FIG. 6, the magnetic field generated in the recording / reproducing gap 4 of the magnetic head device. Is always constant regardless of the direction of the erasing magnetic field.

Example 3. FIG. 7 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted on a 4 MB FDD which is Embodiment 3 of the present invention. Embodiment 3 of the present invention
Compared with the magnetic head device according to the second embodiment of the present invention described above, the magnetic head device of No. 2 has a winding number between the recording / reproducing coil terminal 7a and the recording / reproducing coil center tap 7b, which is the first recording / reproducing coil, and The number of turns between the recording / reproducing coil center tap 7b which is the recording / reproducing coil and the recording / reproducing coil terminal 7c is the same.

In FIG. 7, 23 is a current source for determining the magnitude of the recording current, 24 is a switch for connecting the first recording / reproducing coil to the current source 23, and 25 is a current for the second recording / reproducing coil. A switch for connecting to the source 23. 26 bypasses the current flowing through the current source 23,
Is a current limiting circuit for making the current flowing through the second recording / reproducing coil smaller than the current flowing through the second recording / reproducing coil, 26a is a diode, and 26b is a resistor. Here, the current source 23 and the switches 24 and 25 are incorporated in a head IC which is usually commercially available.

When data is recorded on the medium using the magnetic head device and the recording circuit (recording current driver circuit) configured as shown in FIG. 7, a recording current is passed through the first recording / reproducing coil. The magnetomotive force generated when a recording current is passed through the second recording / reproducing coil is smaller than the magnetomotive force generated sometimes, but due to the magnetic interference with the erasing magnetic flux, the recording of the magnetic head device shown in FIG. The magnitude of the magnetic field generated in the reproducing gap 4 is always constant regardless of the direction of the erase magnetic field.

Example 4. 8 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted on a 4 MB FDD which is Embodiment 4 of the present invention, and FIG. 9 is a timing chart showing the operation of the magnetic head device and the recording circuit of FIG. . The magnetic head device according to the fourth embodiment of the present invention is different from the magnetic head device according to the first embodiment of the present invention in that only the recording / reproducing coil 7 has the recording / reproducing coil terminals 7a and 7c. The tap 7b does not exist. In FIG. 8, 23 is a current source that determines the magnitude of the recording current, 24 is a switch for connecting the recording / reproducing coil 7 to the current source 23, and 27 is a flip-flop that inverts according to the recorded data, which does not record data. Sometimes FIG. 9
It is fixed to "L" by the write gate shown in FIG.

In the magnetic head device and the recording circuit (recording current driver circuit) configured as shown in FIG. 8, a recording current flows through the recording / reproducing coil 7 by closing the switch 24, and at this time, recording / reproducing. The magnetic field generated in the gap 4 is opposite to the direction of the magnetic field generated in the erase gap 5. When data is recorded on the medium using the magnetic head device shown in FIG. 8, first, the medium is magnetized in one direction using the erase gap 5. In this state,
9, the flip-flop 27 is inverted by the recording data, and the recording current flows only when the flip-flop 27 is "H" as shown in Fig. 9. As a result, the recording / reproducing gap 4 of the magnetic head device is generated. The magnetic field creates a magnetization pattern along the recorded data on the medium.

[0036]

As described above, the 4MBFDD of the present invention
According to the above, according to the preceding erasing method, a magnetic head device having a configuration in which a non-magnetic separator, which is a magnetic separation layer, does not exist in the first magnetic core is mounted, and at the time of data recording, a recording / reproducing magnetic field is used. Since the magnetomotive force generated in the circuit is controlled so as to change depending on the direction, the 4MBFDD can be produced at the same low cost as the conventional magnetic head device of this type.
And a 4 MB FDD using this magnetic head device and peripheral circuits can secure a backward compatibility characteristic and obtain a margin in which the device performance has no practical problem. It has excellent effects such as being able to.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted on a 4 MB FDD according to a first embodiment of the present invention.

FIG. 2 is an enlarged view showing a configuration of a gap portion viewed from a medium sliding surface in the magnetic head device of FIG.

3 is a diagram showing a magnetization pattern on a medium recorded by the magnetic head device of FIG.

FIG. 4 is a diagram for explaining that the recording magnetization amount is increased by increasing the recording / reproducing gap length in the magnetic head device of FIG.

FIG. 5 is a diagram showing a reproduction output waveform when recording / reproducing is performed by a conventional magnetic head device.

FIG. 6 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted in a 4 MB FDD which is Embodiment 2 of the present invention.

FIG. 7 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted in a 4 MB FDD which is Embodiment 3 of the present invention.

FIG. 8 is a perspective view showing a configuration and a recording circuit of a magnetic head device mounted in a 4 MB FDD that is Embodiment 4 of the present invention.

9 is a timing chart showing the operation of the magnetic head device and the recording circuit of FIG.

FIG. 10 is a perspective view showing a configuration of a magnetic head device mounted in a conventional 2MB FDD.

11 is an enlarged view showing a configuration of a gap portion viewed from a medium sliding surface in the magnetic head device of FIG.

FIG. 12 is a perspective view showing a configuration of a magnetic head device mounted on another example of a conventional 2MB FDD.

13 is an enlarged view showing a configuration of a gap portion viewed from a medium sliding surface in the magnetic head device of FIG.

FIG. 14 is a diagram showing a magnetization pattern on a medium recorded by a conventional magnetic head device.

FIG. 15 is a timing chart showing an operating principle of a recording circuit of a magnetic head device mounted in a conventional 2MB FDD and a diagram showing a reproduction output waveform of the magnetic head device.

[Explanation of symbols]

 1 first magnetic core 2 second magnetic core 3 third magnetic core 4 recording / reproducing gap 4a recording / reproducing gap length 5 erasing gap 6a, 6b back core 7 recording / reproducing coil 7a, 7c recording / reproducing coil terminal 7b recording / reproducing coil Center tap 8 Erase coil 8a, 8b Erase coil terminal 9, 10 Mold glass 11 Magnetization pattern 12 DC erase area 20 First recording current driver 21 Second recording current driver 22 Erase current driver 23 Current source 24, 25 Switch 26 Current Limiting circuit 26a diode 26b resistor 27 flip-flop

Claims (1)

[Claims] 1. A 4-megabyte flexible disk device capable of recording / reproducing data having an unformatted storage capacity of 4 megabytes according to the MFM recording method, and as a magnetic head mounted therein, two magnetic gaps for recording / reproducing and erasing. A magnetic circuit is formed by a magnetic core to which a separable back core is added, and the magnetic core sandwiched between the two magnetic gaps is formed into an integrated structure without a magnetic separation layer. An erase magnetic circuit having a gap length of 0.45 μm or more and 0.55 μm or less, a recording / reproducing coil wound around the recording / reproducing magnetic circuit having the recording / reproducing magnetic gap, and an erase magnetic circuit having the erasing magnetic gap. Has a structure in which an erasing coil is wound, and the magnetic field generated by the erasing magnetic circuit is erased when the data is recorded. To compensate for the interference, 4 megabytes flexible disk apparatus characterized by comprising means for controlling to vary the magnetomotive force generated in the recording reproducing magnetic circuit by its direction.