reference will now be made in detail to the preferred embodiments of the present invention , examples of which are illustrated in the accompanying drawings . the present invention is directed to discriminating a dvd group and a cd group on the basis of levels of a focus search wave form detected at an fzc position , discriminating whether the above discriminated disk in the same group is a recordable disk on the basis of the level of a focus error signal , and discriminating a dvd - ram and a dvd - rw in the dvd group on the basis of a level of a tracking error signal obtained by free running . a method for discriminating a type of an optical recording medium in accordance with the present invention will now be described with reference to the accompanying drawings . fig2 is a schematic block diagram of an apparatus for discriminating a type of an optical recording medium in accordance with the present invention . as shown in the drawing , the apparatus for discriminating a type of an optical recording medium includes an fzc generation unit 201 for detecting a focus zero cross ( fzc ) position from a focus error signal fe inputted from an rf and servo error generation unit 104 ; an rf level detection unit 201 for detecting a level of an rf signal inputted from the rf and servo error generation unit 104 ; a focus search level detection unit 203 for detecting a level of a focus search wave form ( f - sch ) inputted at the fzc position ; an fe level detection unit 204 for detecting a level of a focus error signal fe inputted from the rf and servo error generation unit 104 ; a te level detection unit 206 for detecting a level of an inputted tracking error signal te ; and a disk discriminating unit 206 for discriminating a type of a disk by using the levels of the signals outputted from each unit 202 ˜ 205 . all these elements are operatively coupled . fig3 a through 3c show examples of wave forms of a disk in a dvd group detected by using an optical system and a light source fit to the dvd group in accordance with the present invention , of which fig3 a sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a dvd - rw disk is inserted , fig3 b sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a dvd - rom disk is inserted , and fig3 c sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a dvd - ram disk is inserted . fig4 a through 4c show enlarged portions of the wave forms of fig3 a through 3c , respectively , at arbitrary positions . fig5 a through 5c show wave forms of a disk of a cd group detected by using an optical system and a light source fit to the dvd group in accordance with the present invention , of which fig5 a sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a cd - rom is inserted , fig5 b sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a cd - rw is inserted , fig5 c sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a cd - r ( coloring group ) is inserted , and fig5 d sequentially illustrates an rf , a te , an fe and a focus search wave form ( f - sch ) detected when a cd - r ( metal group ) is inserted . fig6 a through 6d show enlarged portions of the wave forms of fig5 a through 5d , respectively , at arbitrary positions in accordance with the present invention . fig7 a through 7c show examples of wave forms of a disk of a dvd group detected during free running in accordance with the present invention , of which fig7 a sequentially illustrates an fe and a te wave form when the dvd - ram is inserted , fig7 b sequentially illustrates an fe and a te wave form when the dvd - rom is inserted , and fig7 c sequentially illustrates an fe and a te wave form when the dvd - rw is inserted . fig8 is an example of a comparison table showing variations of rf , fe , fzc , te and wbl according to the type of an optical disk in accordance with the present invention , based on which a type of a disk is discriminated in the present invention . fig9 a and 9b are flow charts of a process of a method for discriminating a type of an optical disk in accordance with the present invention . the method for discriminating a type of an optical disk in accordance with the present invention will now be described with reference to fig9 a and 9b . in the apparatus constructed according to the present invention , when a power is on for its drive , an ld power and an arbitrary optical system are set as an initial set value ( stage : 901 ). in one embodiment of the present invention , it is assumed that the dvd optical system is set . and , it is checked whether or not there is a disk ( stage : 902 ). that is , it is judged whether a disk was mounted for the set optical system after a disk was inserted . if it is judged that a disk was mounted , a focus actuator is set at an initial position and a type of the disk is discriminated . in this respect , in terms of accuracy with respect to discriminating the disk , a number of repetition times for discrimination is set ( stage : 903 ). subsequently , the optical pick - up 102 starts focus - searching , that is , a focus - searching up , under the control of the servo controlling unit 106 ( stage : 904 ). simultaneously , the rf and servo error generation unit 104 detects an rf signal , a focus error signal fe or a tracking error signal te from an electric signal outputted from the optical detector of the optical pick up 102 and outputs the rf signal to the rf level detection unit , the fe signal to the fzc generation unit 201 and to the fe level detection unit 204 , and the te signal to the te level detection unit 205 . upon receipt of the fe signal , the fzc generation unit 201 detects a position where the fe signal becomes ‘ 0 ’ as the fzc position , that is , a position of a corner stone , and outputs it to the focus search level detection unit 203 . at this time , since the fzc may or may not be generated according to the type of disks , the rf level detection unit 202 detects the level of the inputted rf signal and the fe level detection unit 204 detects the level of the inputted fe signal during searching up , and respectively output the signals to the disk discriminating unit 206 ( stage : 905 ). and , when an fzc position is detected by the fzc generation unit 201 ( stage : 906 ), the focus search level detection unit 203 detects a voltage level of the focus search wave form at the fzc position and outputs it to the disk discriminating unit 206 in order to discriminate whether the inserted disk belongs to the cd group or the dvd group ( stage : 907 ). at this time , in case that the fe level is low , the fzc may not be detected . accordingly , if no fzc is detected at the stage 906 , the voltage level of focus search wave form would not be detected . thus , in this case , it is marked that no focus search level was detected . subsequently , it is judged whether the focus - searching up was completed ( stage : 908 ). at this time , if it is judged that the focus - searching up was not completed , it returns to the stage 905 and the following processes are performed , so that the rf , the fe and the focus search wave form are successively detected during the focus - searching up interval . meanwhile , if it is judged that the focus searching up was completed , the disk discriminating unit 206 obtains and stores a maximum value and a minimum value , that is , peak - to - peak voltages , of the inputted fe level and the rf level in order to discriminate the type of the disk in the same group as discriminated by the level of the focus search voltage wave form , and executes focus searching down to the initial position ( stage : 909 ). after the focus searching down is completed ( stage : 910 ), it is judged whether the number of repetition times set at the stage 903 was completed . if the number of repetition times was not completed , it returns to the stage 903 ( stage : 911 ). that is , the stages 904 ˜ 911 are repeatedly performed as many as the number of repetition times set at the stage 903 . and then , an average value of the maximum value and an average value of the minimum value are obtained for each of the fe and the re detected each time , and an average value of the focus search wave form voltage level is also obtained ( stage : 912 ). after the above processes are performed , the disk discriminating unit 206 discriminates a type of the inserted disk by using the data ( stage : 913 ). that is , in the present invention , when a disk is inserted , focus searching is first performed to discriminate whether the inserted disk belongs to the cd group or to the dvd group . in this respect , the focus searching refers to searching a position which is the best focused by moving the objective lens within the optical pick - up in the up - and - down direction , that is , in the focus axis direction , for which a wave form of the voltage applied to the focus actuation is called a focus search wave form ( f - sch ). at this time , the image focused on the optical detector is changed depending on the focus state . the position where a focus error signal is ‘ 0 ’, that is , the position which is the best focused is called fzc position . namely , the fzc position is a slicing position by taking the focus error signal as a reference level . accordingly , in the present invention , while focus searching is performed by the light source ( i . e ., 650 nm or 635 nm ) outputted from a dvd laser diode , the discrimination is made whether the inserted disk belongs to the cd group or to the dvd group by using the voltage level of the focus search wave form detected at the fzc position . in this respect , a light source having a 780 nm wave length , that is , a cd light source , may be used , but in the present invention , a dvd light source is used with its advantage of better distinction because its wave length and focal length are short . that is , referring to the fzc positions of the dvd group disks as shown in fig3 a through 3c and the fzc positions of the cd group disks as shown in fig5 a through 5d , it is noted that the fzc positions of the dvd group disk and of the cd group disk are different from each other due to the structural difference ( i . e ., cd is of 1 . 2 nm and dvd is of 0 . 6 nm ), while those disks belonging to the same group have the same positions . accordingly , the disk discriminating unit 206 compares the voltage level of the focus search wave form detected at the fzc position with an arbitrarily pre - set threshold value , thereby judging whether the inserted disk belong to the cd group or to the dvd group . for example , if the voltage level of the focus search wave form detected at the fzc position is greater than the pre - set threshold value , it is judged as the cd group disk ; or if the voltage level of the focus search wave form detected at the fzc position is smaller than the pre - set threshold value , it is judged as the dvd group disk . meanwhile , if the fe level is so low that no fzc is generated ( referring to fig6 b through 6 d ), no focus search level is detected . in this case , it is judged as the cd group disk . after discriminating the cd group disk or the dvd group disk , it is necessary to discriminate whether it is a reproducing only disk or a recordable disk as they belong to the same group . in the same group , a disk can be discriminated by using the vpp of the fe signal or the normalized factor of the rf level . first , the cd group will now be described with reference to fig5 a through 5d or fig6 a through 6d . referring to fig5 a and 6a , in case of the cd - rom , the maximum value and the minimum value , that is , the vpp of the fe and of the rf is great for the wavelength of 650 nm or the wavelength of 780 nm . and , referring to fig5 b and 6b , in case of the cd - rw , the vpp of the fe and the rf has some size ( some level ) for the wave length of 650 nm but has the smallest value for the 780 nm wavelength . meanwhile , in case of the cd - r , as shown in fig5 c and 6c , since the coloring group has no reflectivity , the vpp of the fe and of the rf has the smallest value for the wave length of 650 nm . this is the same for the metal group of the cd - r . but , for the wave length of 780 nm , the vpp of the fe and of the rf is great in both the coloring group and the metal group . namely , the cd - rom is a little dependent on the wave length of the laser diode ( ld ), while the cd - rw and the cd - r are susceptible to the wave length characteristic of the laser diode . accordingly , in case of the dvd light source having 650 nm wavelength , the vpp of the fe and the rf is obtained in the sequential order of cd - rom & gt ; cd - rw & gt ; cd - r . therefore , after a plurality of threshold values are set differentiating the cd - rom , the cd - rw and the cd - r , when the vpp of the fe or the vpp of the rf is compared with the threshold values , a type of a cd can be discriminated . for example , on the assumption that the threshold values are set as vth 1 and vth 2 for the fe signal and vth 1 is greater than vth 2 , if the vpp of the fe signal measured by the dvd optical system is greater than vth 1 , a type of the inserted disk is discriminated as the cd - rom ; if the vpp of the fe signal measured by the dvd optical system is smaller than vth 1 and greater than vth 2 , a type of the inserted disk is discriminated as the cd - rw ; and if the vpp of the fe signal measured by the dvd optical system is smaller than vth 2 , a type of the inserted disk is discriminated as the cd - r . after the type of the inserted disk is discriminated as the cd group disk through the processes , it is discriminated whether it is a recordable disk or a reproducing only disk , based on which a cd optical system and the laser diode are selected corresponding to the discriminated disk ( stage : 915 ). in this respect , in case of the cd group disk , the data detected by using the dvd optical system may not be sufficient to discriminate it . thus , in terms of verification , a laser diode and an optical system for cd are selected and the disk discriminating processes are performed by using the cd optical system , thereby re - confirming the type of the discriminated disk ( stage : 916 ). thereafter , after the focus servo is on by the cd optical system and the light source , the maximum value , that is , the peak - to - peak voltage ( vpp ), of the tracking error signal detected at the moment is detected ( stage : 917 ). the maximum value of the tracking error signal can be used as a verification for the discriminated result . and , after a disk recognizing number corresponding to the discriminated disk , that is , an id , is set ( stage : 918 ), a servo system ( that is , tracking , focus , sled servo ) corresponding to the set disk id is operated ( stage : 923 ). by operating the servo system at the stage 923 , a disk data can be read from the inserted disk , thereby re - confirming the correctness of the discriminated disk . if the type of the inserted disk is accurately discriminated , the servo is quickly stabilized , so that the quality of the data to be recorded or reproduced can be improved significantly . meanwhile , in case where the inserted disk is discriminated as the dvd group by the comparison of the voltage level of the focus search wave form , as shown in fig3 a through 3c or fig4 a through 4c , a type of the dvd can be discriminated by the vpp of the fe signal or the rf signal . that is , as shown in fig3 b and 4b , in case of the dvd - rom , the vpp of the fe and of the rf , that is , the maximum value and the minimum value are great . and , as shown in fig3 a and 4a , in case of the dvd - rw , the vpp of the fe and of the rf has some size , that is , some level . and , as shown in fig3 c and 4c , in case of the dvd - ram , the vpp of the fe and of the rf is the smallest . this would say that in case of a dvd light source having 650 nm wavelength , the vpp of the fe and of the rf is great in the order of dvd - rom & gt ; dvd - rw & gt ; dvd - ram . thus , like the cd group disk , by setting a plurality of threshold values discriminating the dvd - rom , dvd - rw and dvd - ram and comparing them with the vpp of the fe or the vpp of the rf , the type of the dvd can be discriminated . for example , on the assumption that threshold values for the fe signal are vth 3 and vth 4 and vth 3 is greater than vth 4 , if the vpp of the fe signal measured by the dvd optical system is greater than vth 3 , the inserted disk is judged as the dvd - rom ; if the vpp of the fe signal measured by the dvd optical system is smaller than vth 3 and greater than vth 4 , the inserted disk is judged as the dvd - rw ; and if the vpp of the fe signal measured by the dvd optical system is smaller than vth 4 , the inserted disk is judged as the dvd - ram . after the type of the inserted disk is judged as the dvd group disk and then it is judged whether it is a recordable disk or a reproducing only disk , the focus servo is on ( stage : 919 ) and the maximum value of the tracking error signal as detected , that is , the peak - to - peak voltage ( vpp ), is detected ( stage : 920 ). namely , in case of the dvd group disk , in order to obtain more accurate data , the tracking error signal can be used for a verification whether the dvd - ram and the dvd - rw were properly discriminated after the tracking error signal was detected in a state of free running . the free running refers to detecting a tracking error signal by rotating only a disk without moving the pick - up in a state that a tracking servo is in an off state and a focus servo is in an on state . for example , the tracking error signal can be detected by a push - pull method . at this time , due to the depth difference between the land and the groove ( dvd - ram is of λ / 6 and dvd - rw is of λ / 12 ), there is much difference between the levels of the te signals detected from the dvd - ram and dvd - rw . that is , as shown in fig7 a through 7c , the level of the te signal of the dvd - ram is the greatest , the level of the te signal of the dvd - rom is the smallest , and the level of the te signal of the dvd - rw is smaller than that of the dvd - ram and greater than that of the dvd - rom . therefore , like the above case , by setting a plurality of threshold values for discriminating the dvd - rom , the dvd - rw and the dvd - ram and comparing the vpp of the te with the threshold values , it is verified whether the type of the dvd was properly discriminated ( stage : 921 ). at this time , the tracking error signal obtained by free running may be used for discrimination instead of the rf signal or the fe signal as well as being used for verification . thereafter , a disk id corresponding to the discriminated disk is set ( stage : 922 ), and a servo system ( that is , tracking , focus , sled servo , etc .) is on ( stage : 923 ). in the stage 923 , when the servo system is on , since the disk information can be read out from the inserted disk , it is re - confirmed whether the disk was accurately discriminated . likewise in the cd , as the type of the inserted disk of the dvd group is accurately discriminated , the servo is quickly stabilized , and thus , the quality of the data to be recorded or reproduced can be improved significantly . as so far described , according to the method for discriminating a type of an optical recording medium ( e . g ., a disk ) of the present invention , when the disk is inserted , the focus searching is performed , and it is judged whether the inserted disk is a cd group disk or a dvd group disk by using the voltage level of the focus search wave form detected at the fzc position . subsequently , after it is discriminated whether the discriminated disk is a recordable disk or a reproducing only disk in the same group disk by using the fe or rf level , a servo system is constructed corresponding to the discriminated disk , so that the disk is accurately discriminated , and thus , the servo is stably operated and the initial operation for recording / reproducing can be quickly stabilized . in another embodiment , the dvd - rw , the dvd - ram and the dvd - rom of the dvd group can be discriminated on the basis of the te level obtained by free running . the disk can be accurately discriminated , so that the servo can be stabilized more quickly . also , the type of the cd group disk or the dvd group disk is automatically discriminated during the initial focus - searching , so that an error of the recording / reproducing operation can be reduced in a system of combination cd and dvd . as the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof , it should also be understood that the above - described embodiments are not limited by any of the details of the foregoing description , unless otherwise specified , but rather should be construed broadly within its spirit and scope as defined in the appended claims , and therefore all changes and modifications that fall within the meets and bounds of the claims , or equivalence of such meets and bounds are therefore intended to be embraced by the appended claims .