CA1325849C - Magnetic recording medium and method of determining whether the medium is true or false - Google Patents
Magnetic recording medium and method of determining whether the medium is true or falseInfo
- Publication number
- CA1325849C CA1325849C CA000564281A CA564281A CA1325849C CA 1325849 C CA1325849 C CA 1325849C CA 000564281 A CA000564281 A CA 000564281A CA 564281 A CA564281 A CA 564281A CA 1325849 C CA1325849 C CA 1325849C
- Authority
- CA
- Canada
- Prior art keywords
- magnetic
- code
- recording medium
- truth
- medium
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
- G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
- G06K19/08—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means
- G06K19/10—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards
- G06K19/12—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code using markings of different kinds or more than one marking of the same kind in the same record carrier, e.g. one marking being sensed by optical and the other by magnetic means at least one kind of marking being used for authentication, e.g. of credit or identity cards the marking being sensed by magnetic means
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
- G06K7/00—Methods or arrangements for sensing record carriers, e.g. for reading patterns
- G06K7/08—Methods or arrangements for sensing record carriers, e.g. for reading patterns by means detecting the change of an electrostatic or magnetic field, e.g. by detecting change of capacitance between electrodes
- G06K7/082—Methods or arrangements for sensing record carriers, e.g. for reading patterns by means detecting the change of an electrostatic or magnetic field, e.g. by detecting change of capacitance between electrodes using inductive or magnetic sensors
- G06K7/083—Methods or arrangements for sensing record carriers, e.g. for reading patterns by means detecting the change of an electrostatic or magnetic field, e.g. by detecting change of capacitance between electrodes using inductive or magnetic sensors inductive
- G06K7/084—Methods or arrangements for sensing record carriers, e.g. for reading patterns by means detecting the change of an electrostatic or magnetic field, e.g. by detecting change of capacitance between electrodes using inductive or magnetic sensors inductive sensing magnetic material by relative movement detecting flux changes without altering its magnetised state
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Artificial Intelligence (AREA)
- Computer Vision & Pattern Recognition (AREA)
- Control Of Vending Devices And Auxiliary Devices For Vending Devices (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
A magnetic recording medium includes a truth determining code for determining whether the medium is true or false. The truth determining code is indicated by a magnetic polarity at at least an edge of the medium. A method of determining whether the medium is true or false comprises the steps of detecting a magnetic polarity at an edge of the magnetic recording medium, and collating a combination of the magnetic polarity with a proper combination of the magnetic polarity.
A magnetic recording medium includes a truth determining code for determining whether the medium is true or false. The truth determining code is indicated by a magnetic polarity at at least an edge of the medium. A method of determining whether the medium is true or false comprises the steps of detecting a magnetic polarity at an edge of the magnetic recording medium, and collating a combination of the magnetic polarity with a proper combination of the magnetic polarity.
Description
132~gl~
The present invention relates to a magnetic recording medium and a method of determining whether the medium is true or false, and more particularly to an improvement in security of the magnetic recording medium.
The present invention is adapted to a magnetic recording medium, e.g., a magnetic card requiring an unfair use preventing function and a forgery and alteration preventing function.
Conventionally, the security or protection of the magnetic card, for example, is improved by a method wherein azimuth magnetic recording (this corresponds to the case of Y ~ 90 at the magnetic recording described in Fig. 1 of Canadian Patent No. 1,193,365, issued September 10, 1985, to EMI Li~ited) is carried out to prevent the forgery by a usual reader-writer, a method using a magnetic bar code, or a method using a magnetic mark. The azimuth magnetic recording and reproduction are effected by means of a magnetic head as disclosed in U.S. Patent No. 4,639,812, issued January 27, 1987, to Nakamichi Corporation.
However, the conventional methods as mentioned above require a special magnetic card and a special reader-writer, causing complication of a card system.
According to one aspect of the present invention, there is provided a magnetic recording medium having a magnetic layer, said magnetic layer including at least one magnetic recording track formed in said magnetic layer in one direction, at least one edge of said recording medium being oriented perpendicular to the direction of the recording track and bearing a truth determining code, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer, said truth determining code having a predetermined relationship to ~k , 1 3 2 ~
the contents recorded in the recording track.
Preferably, the predetermined positions include both edges of the recording track.
According to another aspect of the present invention, there is provided a method of determining whether a magnetic recording medium having a magnetic layer and at least one magnetic recording track formed in the magnetic layer is authentic, comprising the steps of:
detecting polarities of magnetic poles formed at predetermined positions of the magnetic layer at at least one edge of the medium perpendicular to a direction of the recording track so that a truth determining code is formed thereby, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer;
reading the contents recorded in the recording track to form a comparative code to be collated with the truth determining code;
collating the truth determining code with the comparative code; and determining the authenticity of said medium by determining whether the truth determining code has a predetermined relationship to the comparative code.
Preferably, the detecting and reading steps are carried - 30 out by the same magnetic head.
As mentioned above, the truth determining code is recorded at the edge of the magnetic recording medium.
Therefore, it is hard to read the truth determining code by a magnetic viewer or the like. Furthermore, whether the magnetic recording medium is true or false is determined by collating the combination of the magnetic polarity at the ~ 3 2 ~ 9 edge with a proper combination. Therefore, as far as the system of the truth determining code is unknown, it is impossible to forge or alter the magnetic recording medium.
This invention will be further illustrated by way of the accompanying drawings, in which:
The present invention relates to a magnetic recording medium and a method of determining whether the medium is true or false, and more particularly to an improvement in security of the magnetic recording medium.
The present invention is adapted to a magnetic recording medium, e.g., a magnetic card requiring an unfair use preventing function and a forgery and alteration preventing function.
Conventionally, the security or protection of the magnetic card, for example, is improved by a method wherein azimuth magnetic recording (this corresponds to the case of Y ~ 90 at the magnetic recording described in Fig. 1 of Canadian Patent No. 1,193,365, issued September 10, 1985, to EMI Li~ited) is carried out to prevent the forgery by a usual reader-writer, a method using a magnetic bar code, or a method using a magnetic mark. The azimuth magnetic recording and reproduction are effected by means of a magnetic head as disclosed in U.S. Patent No. 4,639,812, issued January 27, 1987, to Nakamichi Corporation.
However, the conventional methods as mentioned above require a special magnetic card and a special reader-writer, causing complication of a card system.
According to one aspect of the present invention, there is provided a magnetic recording medium having a magnetic layer, said magnetic layer including at least one magnetic recording track formed in said magnetic layer in one direction, at least one edge of said recording medium being oriented perpendicular to the direction of the recording track and bearing a truth determining code, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer, said truth determining code having a predetermined relationship to ~k , 1 3 2 ~
the contents recorded in the recording track.
Preferably, the predetermined positions include both edges of the recording track.
According to another aspect of the present invention, there is provided a method of determining whether a magnetic recording medium having a magnetic layer and at least one magnetic recording track formed in the magnetic layer is authentic, comprising the steps of:
detecting polarities of magnetic poles formed at predetermined positions of the magnetic layer at at least one edge of the medium perpendicular to a direction of the recording track so that a truth determining code is formed thereby, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer;
reading the contents recorded in the recording track to form a comparative code to be collated with the truth determining code;
collating the truth determining code with the comparative code; and determining the authenticity of said medium by determining whether the truth determining code has a predetermined relationship to the comparative code.
Preferably, the detecting and reading steps are carried - 30 out by the same magnetic head.
As mentioned above, the truth determining code is recorded at the edge of the magnetic recording medium.
Therefore, it is hard to read the truth determining code by a magnetic viewer or the like. Furthermore, whether the magnetic recording medium is true or false is determined by collating the combination of the magnetic polarity at the ~ 3 2 ~ 9 edge with a proper combination. Therefore, as far as the system of the truth determining code is unknown, it is impossible to forge or alter the magnetic recording medium.
This invention will be further illustrated by way of the accompanying drawings, in which:
- 2~-~, ~
132~9 Fig. 1 is a schematic plan view of a first preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 2 is a schematic plan view of a second preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 3 is a schematic plan view of a third preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 4 is a schematic diagrammatic view of a reader-writer for carrying out a preferred embodiment of the truth determining method according to the present invention; and Fig. 5 is a waveform chart of sensor outputs of magnetic heads.
There will now be described some preferred embodiments of the present invention with reference to the drawings.
Fig. 1 ic a schematic plan view of a first preferred embodiment of the magnetic recording medium according to the present invention.
Referring to Fig. 1, a magnetic card 1 is provided with a magnetic layer whose magnetic polarity is oriented in one direction. The magnetic layer is provided with three magnetic tracks Tl - T3. As appreciated from Fig. 1, the magnetic polarity at opposite edges of the track T2 only is inverted, ''' X
. ., ~ _.
~ ? ~
for example. Therefore, as will be hereinafter described, the combinatlon of N-S-N or S-N-S may be obtained by detecting the magnetic polarity at the edges of the tracks, and this combination may be utilized as a -truth determining code for the magnetic card. In this embodiment, the number of combina-tion is 2 = 8, that is, eight kinds of discrimination may be effected.
The truth determining code may be decided in accordance with a desired content recorded on the tracks Tl - T3, such as personal information and amount of money. For example, when the magnetic card 1 is a prepaid card, a remainder changes every time the card is used. Therefore, the truth determining code is decided in accordance with the remainder, and this code is updated every time the card is used. Accordingly, if the remainder is unfairly altered, such alteration can be easily discovered.
The magnetic card may be easily manufactured by forming the rnagnetic layer to be usually adopted and arbitrarily inverting the magnetic polarity. Thus, any special processes or steps are not necessary.
Fig. 2 is a schematic plan view of a second preferred embodiment of the magnetic recording medium according to the present invention. In this embodiment, a data track Tl is formed independently of tracks Tal and Ta2 including the truth determining code.
~' 1 3 2 ~
Fig. 3 is a schematic plan view of a third preferred embodiment of the magnetic recording medium according to the present invention. In this embodiment, the magnetic polarity at edges El - E6 only is inverted or non-inverted, and such is utilized as the truth determining code. In this case, the number of combination of the polarity becomes 2 .
As the inversion or the non-inversion of the magnetic polarity at the edges only is utilized, such cannot be read by a magnetic viewer. Further, in the case that the magnetic polarity at the edges is not inverted with respect to the orientation of the magnetic polarity of the magnetic layer, it is greatly hard to read a position of the truth determining code.
Fig. 4 is a schematic diagrammatic view of a reader-writer for carrying out a preferred embodiment of the truth determin-ing method according to the present invention, and Fig. 5 is a waveform chart of sensor outputs of magnetic heads.
Referring to Fig. 4, the magnetic card 1 is a prepaid card as shown in Fig. 1, and has three magnetic recording tracks at whose edges the truth determining code is recorded.
The magnetic card 1 is movable by a transfer means 10 in the directions as depicted by a double-headed arrow in Fig. 4, and the information recorded on each track is adapted to be read by magnetic heads MS1 - MS3.
Signals Sl - S3 read are adapted to be input to a signal 132~9 processing unit 11 where signal processing such as amplification and AD conversion is carried out, and the signals thus proces~ed are adapted to be stored in a memory 12.
The information stored in the memory 12 is processed, e.g., calculated or modified by a control unit 13 as required.
The control unit 13 is connected to an input unit 14 such as a ten-key unit for inputting a purchase price, for example.
The control unit 13 is also connected to a sensor 15 for detect-ing the edges of the card 1, a display unit (not shown), etc.
The operation of this embodiment will now be described with reference to Figs. 4 and 5.
First, when the card 1 is inserted into the reader-writer, the transfer means 10 is operated by the control unit 13 to draw the card 1 into the device. When the edge of the card 1 is detected by the sensor 15, the signals S1 - S3 read as the information of the card 1 are stored in the memory 12 after a fixed period of time is elapsed.
Outputs from the magnetic heads MS1 - MS3 are inverted according to the magnetic polarity, and as shown in Fig. 5, the combination of S-N-S at the initial edge and the combina-tion of N-S-N at the final edge are obtained as the truth determining code.
Then, a desired information (remainder or personal information, for example) in the memory 12 is read by the control unit 13, and a proper code is calculated by a .
' . ' ~ .
!
132~9 predetermined operation. Then, the code read at the initial edge and the final edge is collated with the proper code. If the code read accords with the proper code, it is determined that the card 1 is true, and the subsequent operation is carried out. If the disaccordance between the code read and the proper code occurs a predetermined times or more, it is determined that the card 1 has been forged or altered, and the card 1 is not accepted.
If the card 1 is true, a purchase price, for example, is inputby auserwith the input unit 14, the remainder is read by the control unit 13 from the information stored in the memory 12, and the purchase price is substracted from the remainder. Then, the difference is stored again in the memory 12. At this time, when the difference or a fresh remainder is not more thana fixed amount, for example, the truth determining code is modified and stored in the memory 12.
For example, the truth determining code is changed into the combination of S-N-N at the initial edge and the combination of N-S-S at the final edge.
When the necessary processing is ended, the transfer means 10 is operated by the control unit 13 to reverse the card 1.
At this time, the information in the memory 12 is read by the control unit 13, and the information including the truth determining code is written on the tracks Tl - T3 of the card 1 by means of the magnetic heads MS1 - MS3. Then, the card 1 .- , , 4 ~
thus updated is returned to the user.
As described above, the truth determining code is recorded at the edges of the card 1, indicative of the inversion or non-inversion of the magnetic polarity. Therefore, even if the information in the card 1 is merely read by a reader or the like, the card 1 cannot be forged as far as the system of the truth determining code is unknown. Thusly, a greatly high security may be obtained by a simple method.
The above-mentioned embodiments are illustrative and may be modified or changed within the scope of the present inven-tion. For example, the present invention is applicable to the determination of the truth of a general magnetic recording medium.
, '- . - ~.
132~9 Fig. 1 is a schematic plan view of a first preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 2 is a schematic plan view of a second preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 3 is a schematic plan view of a third preferred embodiment of the magnetic recording medium according to the present invention:
Fig. 4 is a schematic diagrammatic view of a reader-writer for carrying out a preferred embodiment of the truth determining method according to the present invention; and Fig. 5 is a waveform chart of sensor outputs of magnetic heads.
There will now be described some preferred embodiments of the present invention with reference to the drawings.
Fig. 1 ic a schematic plan view of a first preferred embodiment of the magnetic recording medium according to the present invention.
Referring to Fig. 1, a magnetic card 1 is provided with a magnetic layer whose magnetic polarity is oriented in one direction. The magnetic layer is provided with three magnetic tracks Tl - T3. As appreciated from Fig. 1, the magnetic polarity at opposite edges of the track T2 only is inverted, ''' X
. ., ~ _.
~ ? ~
for example. Therefore, as will be hereinafter described, the combinatlon of N-S-N or S-N-S may be obtained by detecting the magnetic polarity at the edges of the tracks, and this combination may be utilized as a -truth determining code for the magnetic card. In this embodiment, the number of combina-tion is 2 = 8, that is, eight kinds of discrimination may be effected.
The truth determining code may be decided in accordance with a desired content recorded on the tracks Tl - T3, such as personal information and amount of money. For example, when the magnetic card 1 is a prepaid card, a remainder changes every time the card is used. Therefore, the truth determining code is decided in accordance with the remainder, and this code is updated every time the card is used. Accordingly, if the remainder is unfairly altered, such alteration can be easily discovered.
The magnetic card may be easily manufactured by forming the rnagnetic layer to be usually adopted and arbitrarily inverting the magnetic polarity. Thus, any special processes or steps are not necessary.
Fig. 2 is a schematic plan view of a second preferred embodiment of the magnetic recording medium according to the present invention. In this embodiment, a data track Tl is formed independently of tracks Tal and Ta2 including the truth determining code.
~' 1 3 2 ~
Fig. 3 is a schematic plan view of a third preferred embodiment of the magnetic recording medium according to the present invention. In this embodiment, the magnetic polarity at edges El - E6 only is inverted or non-inverted, and such is utilized as the truth determining code. In this case, the number of combination of the polarity becomes 2 .
As the inversion or the non-inversion of the magnetic polarity at the edges only is utilized, such cannot be read by a magnetic viewer. Further, in the case that the magnetic polarity at the edges is not inverted with respect to the orientation of the magnetic polarity of the magnetic layer, it is greatly hard to read a position of the truth determining code.
Fig. 4 is a schematic diagrammatic view of a reader-writer for carrying out a preferred embodiment of the truth determin-ing method according to the present invention, and Fig. 5 is a waveform chart of sensor outputs of magnetic heads.
Referring to Fig. 4, the magnetic card 1 is a prepaid card as shown in Fig. 1, and has three magnetic recording tracks at whose edges the truth determining code is recorded.
The magnetic card 1 is movable by a transfer means 10 in the directions as depicted by a double-headed arrow in Fig. 4, and the information recorded on each track is adapted to be read by magnetic heads MS1 - MS3.
Signals Sl - S3 read are adapted to be input to a signal 132~9 processing unit 11 where signal processing such as amplification and AD conversion is carried out, and the signals thus proces~ed are adapted to be stored in a memory 12.
The information stored in the memory 12 is processed, e.g., calculated or modified by a control unit 13 as required.
The control unit 13 is connected to an input unit 14 such as a ten-key unit for inputting a purchase price, for example.
The control unit 13 is also connected to a sensor 15 for detect-ing the edges of the card 1, a display unit (not shown), etc.
The operation of this embodiment will now be described with reference to Figs. 4 and 5.
First, when the card 1 is inserted into the reader-writer, the transfer means 10 is operated by the control unit 13 to draw the card 1 into the device. When the edge of the card 1 is detected by the sensor 15, the signals S1 - S3 read as the information of the card 1 are stored in the memory 12 after a fixed period of time is elapsed.
Outputs from the magnetic heads MS1 - MS3 are inverted according to the magnetic polarity, and as shown in Fig. 5, the combination of S-N-S at the initial edge and the combina-tion of N-S-N at the final edge are obtained as the truth determining code.
Then, a desired information (remainder or personal information, for example) in the memory 12 is read by the control unit 13, and a proper code is calculated by a .
' . ' ~ .
!
132~9 predetermined operation. Then, the code read at the initial edge and the final edge is collated with the proper code. If the code read accords with the proper code, it is determined that the card 1 is true, and the subsequent operation is carried out. If the disaccordance between the code read and the proper code occurs a predetermined times or more, it is determined that the card 1 has been forged or altered, and the card 1 is not accepted.
If the card 1 is true, a purchase price, for example, is inputby auserwith the input unit 14, the remainder is read by the control unit 13 from the information stored in the memory 12, and the purchase price is substracted from the remainder. Then, the difference is stored again in the memory 12. At this time, when the difference or a fresh remainder is not more thana fixed amount, for example, the truth determining code is modified and stored in the memory 12.
For example, the truth determining code is changed into the combination of S-N-N at the initial edge and the combination of N-S-S at the final edge.
When the necessary processing is ended, the transfer means 10 is operated by the control unit 13 to reverse the card 1.
At this time, the information in the memory 12 is read by the control unit 13, and the information including the truth determining code is written on the tracks Tl - T3 of the card 1 by means of the magnetic heads MS1 - MS3. Then, the card 1 .- , , 4 ~
thus updated is returned to the user.
As described above, the truth determining code is recorded at the edges of the card 1, indicative of the inversion or non-inversion of the magnetic polarity. Therefore, even if the information in the card 1 is merely read by a reader or the like, the card 1 cannot be forged as far as the system of the truth determining code is unknown. Thusly, a greatly high security may be obtained by a simple method.
The above-mentioned embodiments are illustrative and may be modified or changed within the scope of the present inven-tion. For example, the present invention is applicable to the determination of the truth of a general magnetic recording medium.
, '- . - ~.
Claims (4)
1. A magnetic recording medium having a magnetic layer, said magnetic layer including at least one magnetic recording track formed in said magnetic layer in one direction, at least one edge of said recording medium being oriented perpendicular to the direction of the recording track and bearing a truth determining code, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer, said truth determining code having a predetermined relationship to the contents recorded in the recording track.
2. The magnetic recording medium as defined in Claim 1, wherein said predetermined positions include both edges of the recording track.
3. A method of determining whether a magnetic recording medium having a magnetic layer and at least one magnetic recording track formed in the magnetic layer is authentic, comprising the steps of:
detecting polarities of magnetic poles formed at predetermined positions of the magnetic layer at at least one edge of the medium perpendicular to a direction of the recording track so that a truth determining code is formed thereby, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer;
reading the contents recorded in the recording track to form a comparative code to be collated with the truth determining code;
collating the truth determining code with the comparative code; and determining the authenticity of said medium by determining whether the truth determining code has a predetermined relationship to the comparative code.
detecting polarities of magnetic poles formed at predetermined positions of the magnetic layer at at least one edge of the medium perpendicular to a direction of the recording track so that a truth determining code is formed thereby, said code comprising a combination of polarities of magnetic poles formed at predetermined positions of the magnetic layer;
reading the contents recorded in the recording track to form a comparative code to be collated with the truth determining code;
collating the truth determining code with the comparative code; and determining the authenticity of said medium by determining whether the truth determining code has a predetermined relationship to the comparative code.
4. The method as defined in Claim 3, wherein said detecting step and said reading step are carried out by means of the same kind of magnetic head.
Priority Applications (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| EP88903371A EP0412156B1 (en) | 1988-04-14 | 1988-04-14 | Truth determination method for a magnetic recording medium |
| AU15922/88A AU624786B2 (en) | 1988-04-14 | 1988-04-14 | Magnetic recording medium and truth determination method therefor |
| PCT/JP1988/000369 WO1989009981A1 (en) | 1988-04-14 | 1988-04-14 | Magnetic recording medium and truth determination method therefor |
| CA000564281A CA1325849C (en) | 1988-04-14 | 1988-04-15 | Magnetic recording medium and method of determining whether the medium is true or false |
| US07/818,747 US5160833A (en) | 1986-11-13 | 1992-01-07 | Magnetic recording medium having authenticating poles at its edge |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP1988/000369 WO1989009981A1 (en) | 1988-04-14 | 1988-04-14 | Magnetic recording medium and truth determination method therefor |
| CA000564281A CA1325849C (en) | 1988-04-14 | 1988-04-15 | Magnetic recording medium and method of determining whether the medium is true or false |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1325849C true CA1325849C (en) | 1994-01-04 |
Family
ID=4137846
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000564281A Expired - Fee Related CA1325849C (en) | 1986-11-13 | 1988-04-15 | Magnetic recording medium and method of determining whether the medium is true or false |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1325849C (en) |
-
1988
- 1988-04-15 CA CA000564281A patent/CA1325849C/en not_active Expired - Fee Related
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| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |