GB2178574A

GB2178574A - Preventing copying of a magnetic recording

Info

Publication number: GB2178574A
Application number: GB08617502A
Authority: GB
Inventors: Yoshio Mikame; Fumitomo Ueno
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 1985-07-27
Filing date: 1986-07-17
Publication date: 1987-02-11
Also published as: KR910004627B1; JPH0673221B2; DE3625176A1; GB8617502D0; KR870001528A; JPS6226671A

Abstract

The position of a data bit is preshifted from its normal position at a specified portion of a recording medium when data are recorded, whereby illegal copying is prevented. The shift results in unstable readout of the data from that portion, which can be detected by repeated readout by a diagnostic program to validate the recording. <IMAGE>

Description

SPECIFICATION Method of preventing a magnetic recording medium from its reproduction The present invention relates to a method of preventing a magnetic recording medium from its reproduction.

In modern society flooded with information, magnetically recording devices such as computers are widely used for various fields in factories, offices and individual homes. To operate a computer, there requires cooperation of hardware and software as a program which is a technique of utilization of the computer. A market for the software has spreaded to such extent that various kinds of software products in which data are recorded in a magnetic recording medium such as a floppy disk, a magnetic tape and so on, are produced in many professional offices called "software house".

When a user wishes to operate a computer for a specified purpose, he buy the software such as a floppy disk (original) in which a required program is recorded in a magnetic recording medium. The program recorded could be, however, easily reproduced. If the program is illegally reproduced, effort for developing the software with a great deal of time and expense becomes useless. Accordingly, a problem is that how measures should be taken so that a developed software is not illegally reproduced. There have been proposed various methods of prevention of magnetic recording medium from its illegal reproduction.

However, the proposed methods were insufficient. The reason is as follows. The conventional methods owe a system that utilizes a format other than an ordinary format supported by an operating system (OS) for a computer so that data can not be written-in or read-out by the computer. Accordingly, a user having some professional knowledge will easily find the key. Programs for breaking the copy protection are also commercially available.

It is an object of the present invention to provide a method of preventing a magnetic recording medium from its reproduction by means of a partial modification of hardware without modifying an operating system of software which is common to computers.

The foregoing and the other objects of the present invention have been attained by providing a method of preventing a magnetic recording medium from its reproduction, characterized in that the position of a data bit is preshifted from the normal position of it in a specified portion of a recording medium when data are recorded in the recording medium.

In the drawings: Figure 1 is a timing chart of data bits showing a method of preventing a floppy disk from its reproduction according to an embodiment of the present invention; Figure 2 is a diagram showing an electric circuit for effecting preshifting; Figure 3 is a timing chart obtained by the electric circuit shown in Fig. 2; Figure 4 is a damp list of data recorded in an original magnetic recording medium obtained by reading the medium three times by a read diagnostic instruction; Figure 5 is a damp list of a reproduced product by reading twice by a read diagnostic instruction.

An embodiment of the present invention will be described with reference to drawings.

Fig. 1A is a timing chart of data bits recorded under normal condition; Fig. 1B is a timing chart in which the positions of data bits are preshifted, and Fig. 1C is a timing chart in which the positions of data bits are preshifted in the opposite direction with respect to the normal positions of the data bits.

In the method of preventing a magnetic recording medium from its reproduction, data bits at a specified portion in the medium are recorded by preshifting from the normal positions 0i P1, O, P2 by the quantity of preshift t3, t4 respectively.

With these measures, a reading error is caused at the position where the data bits are preshifted, when the data are read out. Accordingly, it is impossible to reproduce an original record because the reading error is caused at the portion. Even though the reading error is not caused, it is extremely difficult for an end user's recording and reading device to reproduce the original record by shifting the data bits at the specified portion. Accordingly, a check program may be incorporated in a user program of the original record in such a manner that whether or not the data bits are located at the normal positions at the specified portion is examined, and if the positions of the data bits at the specified portion are other than the normal positions, namely, there causes an error, the operation of the user program is continued.In the products reproduced by a user, it is impossible to shift the data bits at the specified portion. Accordingly, the users program can not be subsequently operated.

Usually, in a magnetic recording medium such as a floppy disk, timing of reproduction of data for reading-out are shifted from the timing of data for writing-in. The shift of the timing is called "peak shift". In the case of the data for writing-in, when the distance of the adjacent bits comes closer beyond a predetermined distance, there takes place repulsion of the adjacent bits as shown in Fig. 1A, and the data for reading-out are recorded with a certain amount of shift. Namely, the adjacent bits are shifted from the normal positions 0, P1, O, P2 by t and t2 respectively.Since the amount of shift can be expected depending on a data pattern to be used, the amount of the shift of the data at the time of reading can be cancelled as shown in Fig. 1B by writing the data previously in the opposite direction taking consideration of the expected amount of shift, when the data are read-out. This operation in the writing operation is called preshifting. Integrated circuits for the preshifting are sold by NEC, FUJITSU and other companies. The preshifting is carried out by recording the data at a specified portion of the magnetic recording medium (original record) so as to be inverse to the usual preshifting, namely, the preshifting is applied to produce much amount of shift t3, t4 when the data are read-out, as shown in Fig. 1C.The preshifting is carried out, for instance, by using a floppy disk controller IC"#PD765A/7265" manufactured by NEC, in which the preshift terminals PSO, PS1 are inversely connected to form a writing circuit. Fig. 2 is a diagram showing an electric circuit for causing the preshifting which uses the floppy disk controller IC #PD765A, and Fig. 3 is a timing chart obtained by the abovementioned electric circuit.

A preshift circuit is constituted by a flip-flop circuit of LS175 which generates write data signals having three kinds of delay mode, a clock circuit for shifting 1 which controls the quantity of delay, a circuit in the controller ,uPD765A for generating a gate signal which determines one of the delayed write data signals, and a data selector of LS153 which selects the write data signal delayed. The circuit in the controller ,uPD765A is capable of determining which signal is to be selected, through PSO or PSI. The circuit can be formed by a combination of a shift register and a gate. By using such a circuit, data bits corresponding to the terminals having opposite connection are largely deflected from the normal positions when the data are read-out.Accordingly, the operation of reading-out becomes extremely unstable and a reading error takes place. As a simple determination of illegal reproduction, checking can be made as to whether or not the reading error takes place. If the error occours, the floppy disk examined is considered to be an original record. However, the abovementioned checking method is insufficient since it is impossible to discriminate such error from erros to be detected by a cyclic redundancy check (CRC errors) which has be generally utilized to detect a defect of a magnetic recording medium.

In the present invention, when the data recorded in the magnetic recording medium are read-out by a read diagnotic instruction, the content of the data changes for each print as shown in Fig. 2 because of unstableness in the positions of the data bits. Fig. 2 shows printed copy of the data recorded in a floppy disk as an original record when the reading operation is carried out three times by the read diagnotic instruction. When the reading operations are repeated several times, and if the same data are obtainable for each time, the floppy disk is considered to be an illegally produced product. On the other hand, if the printed data vary for each time, it is determined as an original record. Thus, the present invention provides an effective checking method.

In the above-mentioned embodiment, the preshifting of the data bits at a specified portion is carried out in the direction opposite to the normal direction when data bits are recorded. However, it is possible to preshift data bits at a specified portion in the same direction as usual in which the quantity of preshifting is increased, or to change a data pattern for the preshifting.

In order to increase the quantity of preshifting, the clock for shifting may be elongated.

Specifically, the clock more than 250 ns is used (The clock of 250 ns is usually used in the case of 5 inch 2DD.).

Thus, in accordance with the present invention, data bits at a specified portion in the magnetic recording medium are recorded by shifting the positions of the data bits from the normal positions. Accordingly, it is impossible to reproduce the original record unless a part of hardware is changed, and reproduction of the original record in the magnetic recording medium can be certainly prevented.

Claims

1. A method of preventing a magnetic recording medium from its reproduction, characterized in that the position of a data bit is preshifted from the normal position of it in a specified portion of a recording medium when data are recorded in said recording medium.

2. The method according to Claim 1, wherein the position of said data bit is preshifted in the opposite direction with respect to the normal position.

3. The method according to Claim 1, wherein the quantity of preshifting is increased.

4. The method according to Claim 1, wherein a data pattern for preshifting is changed.

5. A method according to claim 1, substantially as described.