Patent Publication Number: US-RE37503-E

Title: Floppy disk drive device

Description:
This is a continuation of application Ser. No. 08/335,421 filed on Nov. 7, 1994, now U.S. Pat. No. 5,469,421 which is a continuation of application Serial No. 07/915,044, filed Jul. 16, 1992, abandoned which is a continuation of application Ser. No. 07/474,123, filed Jul. 5, 1990, for FLOPPY DISK DRIVE DEVICE, now abandoned.This is one of seven ( 7 ) reissue applications directed to various distinct and separate parts of the floppy disk drive described in U.S. Pat. No.  5 , 610 , 782 , which corresponds to U.S. Ser. No.  08 / 567 , 340 , which is a continuation of U.S. Ser. No.  08 / 335 , 421  filed on Nov.  7 ,  1994 , now U.S. Pat. No.  5 , 469 , 421 , which is a continuation of U.S. Ser. No.  07 / 915 , 044  filed on Jul.  16 ,  1992  abandoned, which is a continuation of U.S. Ser. No.  07 / 474 , 123  filed Jul.  5 ,  1990 , abandoned. Each of the reissue applications was filed on Mar.  23 ,  1998  and is entitled “FLOPPY DISK DRIVE”. The U.S. application Ser. Nos. for the seven ( 7 ) reissue applications are as follows:  09 / 045 , 931 ,  09 / 045 , 901  now abandoned,  09 / 045 , 932  now abandoned,  09 / 046 , 132 ,  09 / 046 , 133 ,  09 / 046 , 131  now abandoned and  09 / 046 , 130 . 
    
    
     TECHNICAL FIELD 
     The present invention is directed generally to a recording/reproducing device for use with, e.g., a computer and a word processor, and more particularly, to a recording/reproducing device for recording or reproducing pieces of desired information on or from a recording medium such as a floppy disk. 
     BACKGROUND ARTS 
     A typical arrangement of this type of recording/reproducing device is that a frame of an apparatus body accommodates a disk driving motor, a carriage having upper and lower heads, a carriage driving motor for moving the carriage and a circuit board incorporating a circuit for controlling operations of the motor and a lead light  read/write head; and the recording medium is loaded into the device to effect recording or reproducing. In recent years, it is desired that the recording/reproducing device be small both in configuration and in thickness with an increasing demand for miniaturizing the computers. 
     A prior art recording/reproducing device disclosed in Japanese Utility Model Laid-Open Publication No. 62-147197 is illustrated in FIGS. 38 and 39. FIG. 38 is a vertical sectional side view of the prior art recording/reproducing device. FIG. 39 is an enlarged view depicting the principal portion thereof. 
     As illustrated in the Figures, a spindle motor  502  serving as a motor for driving the carriage is mounted from underside of a frame  501  in the Figures. Disposed on an upper surface of the spindle motor  502  is a lower carriage  503  fitted with a lower head, on which an upper carriage  504  having an upper head  508   506 is mounted about a rotary fulcrum. A jacket is held between the lower and upper carriages  503  and  504 . Provided on the recording/reproducing device is a holder  505  which moves between a position in which to insert a jacket J and a recording/reproducing position. The upper carriage  504  mounted with the upper head includes a lift member  504 a to separate the upper carriage  504  from the jacket J in linkage with a motion of the holder  505  moving between the inserting position of the jacket J and the recording/reproducing position. 
     For this purpose, in the recording/reproducing device catered for, e.g., a recently developed lap-top computer, as the above-mentioned demand for decreasing a thickness of the device grows, it is required to reduce both a clearance cl between the upper carriage  504  depicted in FIG.  39  and an outer circumference of the recording/reproducing device and a clearance c 2  between the upper head  506  and the jacket J. Based on the prior arts, however, an amount of movement of the upper carriage  504  is determined by a lifting/lowering quantity of the holder  505 . The upper carriage  504  is constructed to rotate about a fitting part to the lower carriage  503 , and hence a scatter with respect to the lifting member  504 a of the upper carriage  504  is expanded several times in a position of the upper head  506  at the top of the upper carriage  504 . When making an attempt to enlarge the clearance c 2  between the jacket J and the upper head  508   506 , the upper carriage  504  grows in configuration in excess of predetermined dimensions of the recording/reproducing device; or reversely, when the priority is given to the dimensions of the recording/reproducing device, it is impossible to obtain a sufficient clearance c 2  between the jacket J and the upper head  508   506 . This situation leads to a problem in which the jacket J acts to damage the upper head  506 . 
     A rotary driving mechanism for a disk in the above-mentioned recording/reproducing device is disclosed in, for instance, Japanese Utility Model Laid-Open Publication No. 61-52351. The construction thereof is depicted in FIGS. 40 through 43. Turning to FIG. 40, there is illustrated a plan view of a conventional disk rotary driving unit. FIG. 41 is a bottom view thereof. FIG. 42 is a vertical sectional view thereof. FIG. 43 is a sectional view schematically illustrating a driving pin part thereof. 
     In these Figures, the symbol D denotes a disk, and H represents a hub thereof. These components are drawn with dotted lines in FIGS. 40 and 41FIG.  42 . The reference numeral  510  designates a rotary driving shaft of the disk D. A chucking lever  512  is pivotally supported about a fulcrum  513  on a rotary plate  511  rotating together with the driving shaft  510 . A spring  515  imparts an axial bias to a driving pin  514  fitted to the chucking lever  512 , while rotational bias is given by a spring  516 . The chucking lever  512 , when the hub H is set to be chucked, as illustrated in FIG. 43, escapes in an arrowed direction r in the Figure while being pushed by the hub H, so far  long as a rotary driving hole h 2  located eccentrically from the center of the hub H does not align in position with the driving pin  514 . Next, as depicted in FIG. 42, the driving pin  514  rotates together with the rotary central shaft  510  by initiating rotations of a rotor  518  of a disk driving motor  517  mounted on an end of the rotary driving shaft  510 . Just when the rotary driving hole h 2  aligns with the driving pin  514 , this pin  514  is protruded into the rotary driving hole h 2  by dint of the spring  515 . On the basis of a positional relationship of the driving pin  514  with respect to the fulcrum  513 , as illustrated in FIG. 40, the driving pin  514 , when rotating the hub H, generates a force acting in an arrowed direction s of the Figure and a force for rotating the hub H. The force in the arrowed direction s of the Figure acts to thrust two inner points of a central hole h 1  of the hub H against the rotary driving shaft  510 , thereby effecting a rotary drive while seeking the center of the hub H. The lower head  519  for recording and reproducing signals on and from the disk D is disposed between a frame  520  of the motor  517  and the disk D. 
     Based on this construction, according to the prior art discussed above, when trying to reduce the thickness of the recording/reproducing device, thicknesswise dimensions are conditional to a space for accommodating the rotor  518  of the motor  517 , the lower carriage  521 , the lower head  519  and the chucking mechanism. This is an obstacle against the reduction in thickness of the device. 
     In particular, as depicted in FIG. 43, the driving pin  514  is pushed by the hub H when chucking the hub H and is moved in the arrowed direction r in the Figure, resulting in provision of a futile space. 
     An additional example is a recording/reproducing device reported on Nikkei Electronics Journal, NO.394 issued in 1986 5—5. This recording/reproducing device is, as illustrated in FIG. 44, constructed such that a disk driving motor  525  is provided coaxially with the disk D defined as a recording medium, a bearing  525 a of the motor  525  is fitted in a positioning hole  526 a bored in a frame  526 , and a motor base  527  is fixed to the frame  526  with Screws  screws. 
     Upper and lower carriages  530  and  531  mounted with upper and lower heads  528  and  529  are guided by a guide shaft  532 . Movement positioning in an arrowed direction j  t of the Figure is effected by use of an unillustrated stepping motor conceived as a carriage driving motor. Attached to a lower surface of the guide shaft  582   532 in the Figure is a circuit board for controlling the disc driving unit and converting signals transmitted from the heads. 
     Besides, the lower carriage  581   531 is arranged to move up to an upper surface of the rotor  525 b of the disk driving motor  525  in the Figure. 
     For this reason, in the case of decreasing the device thickness, it is necessary to make thin both the motor and the frame, because the disk driving motor is disposed downwardly of the frame. It is therefore difficult to reduce the device thickness. A further obstacle against the decrease in the device thickness is the arrangement that a control board is attached to a lower surface of the carriage. It is because the carriage is overlapped thicknesswise with the control board. The carriage is intruded up to an upper surface of the rotor of the disk driving motor, resulting in the difficulty of reducing the device thickness because of superposing the carriage thicknesswise on the rotor. 
     A loading/ejecting mechanism of the disk in the prior art recording/reproducing device is constructed in the following manner. FIG. 45 is a plan view schematically illustrating one example of the conventional recording/reproducing device. FIGS.  48   46 and  47  are vertical sectional side views schematically depicting a standby state of loading a jacket accommodating the disk and a state of mounting the jacket. 
     Referring to these Figures, a shutter releasing lever  535  is provided at its one end with an operating pin  586   536 for releasing a shutter (not shown) of the jacket by engaging with the shutter. The other end of the lever  535  is so fitted to a holder  537  for holding the jacket as to be ratable  rotatable about a fulcrum pin  538 . The lever  535  is constantly so biased as to be rotatable clockwise in FIG.  45 . On a side surface of the holder  537 , a plurality of rolling roller pins  537 a serving as interlocking means are fixed to rolling rollers  537 b to permit rotations of the rolling rollers  537 b, the pins  537 a being biased in an arrowed direction X 1  by a holder spring  541  while engaging with holder guide grooves  540 a of a frame  540 . The roller pins  537 a are positioned to permit impingement upon lifting/lowering cam portions  542 a of a cam member  542  depicted in FIGS. 46 and 47. The cam member  542  is supported on a jacket guide receiving portion  543  conceived as a jacket supporting means embedded into the frame  540  and on a part of a jacket receiving pin  544  serving as a position regulating means. The cam member  542  is so disposed as to be slidable in arrowed directions x 1  and x 2  and is also biased in the arrowed direction x 1  by a cam member spring  545 . An eject member  546  depicted in FIG. 45 is axially supported on a shaft  547  embedded into the frame  540  and rotationally biased anticlockwise in FIG. 45 by means of an eject member spring  548 . The eject member  548   546 includes an impingement portion  546 a which impinges upon a part of the jacket J. The jacket K  J, when being inserted or pulled out, collides with the impingement portion  548 a   546 a, whereby the eject member  548   546 rotates about the shaft  547 . 
     Fixed to a part of the cam member  542  is an eject button  549  illustrated in FIGS.  48   46 and  47  in close proximity to a dressing plate  550  attached to the frame  540 . 
     Based on such a construction, as illustrated in FIG. 46, the jacket J is inserted from an insertion port  550 a in the direction x 2 , in which state the operating pin  536  fixed to the shutter releasing lever  535  shown in FIG. 45 engages with the shutter of the jacket J. The shutter releasing lever  535  is thereby rotated about the fulcrum pin  538  in the anticlockwise direction of FIG. 45 while opening the shutter. Upon a further insertion of the jacket J in the arrowed direction x 2  of FIG. 46, the jacket J impinges on the impingement portion  546 a of the eject member  546 , with the result that the eject member  546  starts rotating clockwise about the shaft  547  in FIG. 45 while resisting the biasing force of the eject member spring  548 . When being further intruded, the jacket J abuts against an impingement portion  537 d of the holder  537 , thereby moving the holder  537  in the arrowed direction x 2 , resisting the biasing force of the holder spring  541 . As shown in FIG. 46, the plurality of rolling rollers  537 b provided on the side surface of the holder  537  are moved down along the guide groove  540  chased in the frame  540  in an arrowed direction z 2  by means of the holder spring  541 . 
     On the other hand, the jacket J inserted into the holder  537  is supportingly received by the jacket receiving pin  544  embedded into the frame  540  and by the jacket receiving portion  843   543 , thus effecting a predetermined positioning process. Subsequently the jacket is seated as illustrated in FIG. 47, in which position recording and reproducing are to be performed. 
     Next, in the case of ejecting the jacket J, the eject button  549  is depressed in the direction x 2  from a state of FIG.  47 . Then, a lifting cam portion  542 a of the cam member  542  impinges upon the rolling roller  537 b of the holder  537 , whereby the holder  537  holding the jacket J slides upwards along a holder guide groove  540 c formed in the frame  540 . Immediately, the eject member  546  is rotated anticlockwise in FIG. 45 by the biasing force of the eject member spring  548 , and the jacket J is thereby ejected in the arrowed direction x 1 . At this time, the shutter releasing lever  535  is made to revert to a position indicated by a solid line of FIG. 45 by dint of a tensile coil spring  539 , thus finishing an ejecting operation. 
     In the above-mentioned prior art jacket loading/ejecting mechanism, however, the cam member  542  guided by the guide pin embedded into the frame  540  slides in the jacket inserting/removing directions to thereby move the holder  537  horizontally to the jacket inserting/removing position and further to the recording/reproducing position. As a result, a load associated with rectilinear sliding of the cam member  542  becomes large, and the cam member  542  increases in configuration because of requiring guide pins  543  and  544  for guiding the holder  537  and also a support member for moving the holder while holding it horizontally. Besides, the cam member has to be disposed between the holder and the frame, resulting in a problem in terms of space. 
     If the jacket is mistakenly inserted, the jacket is intruded from the insertion port  550 a of the dressing plate  550  of FIG. 46 in the arrowed direction X 2  in such a state, for example, the surfaces or the front and the rear of the jacket are reversed. At this time, the operating pin  536  provided on the shutter releasing lever  535  impinges on the top end surface of the jacket J, thereby rotating the lever  535  anticlockwise in FIG.  45 . When the insertion continues, the shutter releasing lever  535  is further rotated in the same direction and behaves to thrust forward the holder  537  while abutting against an impingement portion  537 e of the holder  537 . For this reason, the result is that the same fitting operations are carried out following a trajectory identical with that in the inserting process in the above-described normal state. Consequently, the components incorporated in the device are to be damaged. The cam member  542  is, as discussed above, supported on the jacket receiving portion  543  conceived as a jacket supporting means embedded into the frame  540  as well on a part of the jacket receiving pin  544 defineddefining a position regulating means. The cam member  542  is so located as to be slidable in the arrowed directions X 1  and x 2  and includes the cam portion  542 a on which the plurality of rolling rollers  537 b provided, as depicted in FIG.  48 ,   46 on the side surface of the holder  537  impinge. With this arrangement, when sliding the cam member  542 , the sliding portion increases in area, and there are needed parts for guiding and holding the cam member  542 . Provision of the cam member  542  entails formation of a gap between the frame  540  and the holder  537 , and an additional problem is that the configuration becomes large because of the parallel movement of the holder  587 . 
     As stated earlier, the conventional reproducing device presents a variety of obstacles against miniaturization of the device (reduction in the device thickness). 
     In a recording/reproducing device developed in recent years as an external storage unit of a variety of electronic appliances associated with computers, there are widely spread a floppy disk drive (hereinafter abbreviated to FDD). A  , a hard disk drive (abbreviated to HDD), an optical disk drive (abbreviated to ODD) and a tape streamer. Sizes of outer shapes and fitting dimensions thereof are substantially standardized depending on a size of the recording medium. Take the FDD for instance, typically three types of FDDs are available, i.e., a 3.5-inch type, d  a 5.25-inch type (generally known as a 5-inch type and the representation is the same with this description) and a  an 8-inch type. The recording medium used for a single unit of electronic appliance typically comes under one size, which causes inconvenience in terms of general purposes. 
     To cope with this, there was proposed a recording/reproducing device capable of recording and reproducing by employing both an initially used disk and another disk having a different size, the device being disclosed in, Japanese Utility Model Laid-Open Publication No.63-11792. The construction thereof is shown in FIGS. 48 and 49. 
     Turning first to FIG. 48, there is illustrated a perspective view of an outline of the conventional recording/reproducing device in an electronic appliance such as a computer. FIG.  49 . is a front elevation thereof. 
     An arrangement of the recording/reproducing device, depicted in FIGS. 48 and 49, for use with the electronic appliance is given as follows. For example, a 3.5-inch standardized recording/reproducing device  603  in accordance with a recent tendency of miniaturization incorporated in a chassis  602  of an electronic appliance body  601 , the chassis  602  having the same size and the same mounting structure as those of the chassis of the FDD (hereinafter referred to as a 5-inch standardized FDD) which is standardized corresponding to, e.g., an initially used 5-inch disk. Attached to a front surface of the chassis  602  is a front bezel  604  having much the same size as that of, e.g., a 5-inch FDD. The front bezel  604  is formed with an insertion port  604 a for loading the inch disk. Provided in rear of the recording/reproducing device  603  is a relay board  605  exhibiting the same interface function as that of, e.g., the 5-inch FDD. In a variety of electronic appliances each mounted with, e.g., the 5-inch FDD and composed of a body  601  formed with an opening for admitting the front bezel, the recording/reproducing device is completely replaceable with the 5-inch FDD. 
     The above-mentioned type is, however, classified as, e.g., a 3.5-inch recording/reproducing device miniaturized smaller than the 5-inch FDD and having an interface function identical with that of the 5-inch FDD. For instance, in many kinds of electronic appliances each mounted with, e.g., 5-inch FDD, the recording/reproducing device is completely replaceable with the 5-inch FDD. Hence, when replacing the recording/reproducing device even in a system which has hitherto been utilized, software recorded on a 3.5-inch recording medium can be used instead of the software which has already been recorded on a 5-inch recording medium in the conventional system as it is. The initial purpose can thus be accomplished. There arise, however, the following defects in association with a technical tendency of nowadays. 
     There can be seen a remarkable advancement in technologies pertaining to a variety of electronic appliances related to up-to-date computers. In particular, a technical enhancement combined with the software is most sophisticated, and therefore the softhouse-based  software- based  business is aggressively expanded. 
     The softhouse-based  software- based  business is developed with brains, and its technical growth is increasingly accelerated. On the other hand, it is required that a good deal of assets be invested in the development of technologies of hardware, i.e., multiple computer-based electronic appliances. Life cycles of the hardware are relatively long as compared with the software, and it is not easy to improve the hardware because of requiring highly sophisticated techniques of specialty. In the actual systems, there still exist hardware here and there which can not come up with the technical advancement on the part of software. This is the real situation. This imbalance may be a big obstacle against the development of the general system. What is needed especially in the sector of software technologies is to facilitate an expansion of the general system by freely systematizing the FDDs, HDDs, ODDs and tape streamers which have been standardized and spread over as external storage devices of many kinds of electronic appliances. 
     Accordingly, it is the first object of the present invention, which has been devised under such circumstances, to miniaturize the recording/reproducing device to the greatest possible degree, and particularly, to reduce a thickness thereof. 
     Another object of the invention is to shrink a space for accommodating a variety of electronic appliances such as computers by virtue of the reductions both in configuration and in thickness of the recording/reproducing device and also to facilitate both functional improvements thereof and an expansion of the system. 
     DISCLOSURE OF THE INVENTION 
     According to the present invention, there is provided a recording/reproducing device comprising: at least a disk driving motor described above; a carriage including upper and lower heads; a carriage driving motor; a circuit board having a circuit for controlling operations of a read/write and of the motors; and a device body frame. The recording/reproducing device is made as small, i.e., thin as possible. To be more specific, a thickness of the device as a whole is set smaller than 20.5 mm. 
     A means for making the device thin is attained by taking the following components and arrangement. 
     For example, a rotor magnet of the disk driving motor involves the use of a rare earth group magnet. Where the rare earth magnet is employed, the same or higher performance than in the prior art can be secured even if the magnet is smaller than the conventional one. Hence, an outside diameter or an axis-directional length of the disk driving motor can be reduced. The rare earth group magnet is effective especially in reducing the thickness of the whole device when employing a spindle motor coaxial with the disk as a disk driving motor. 
     If the placement is made without causing planar overlapping of the carriage having the upper and lower heads with the disk driving motor, the device can be decreased in thickness on the whole. In the case of disposing a circuit board and a guide shaft with a deviation on the plane, the device thickness can likewise be reduced. Where neodymium ferrous boron is used as a rotor magnet for the carriage driving motor, sufficient torque can be obtained even in the case of miniaturization, and the whole device can be decreased in thickness. 
     Besides, it is possible to make the device still thinner by adequate and selective combinations of the above-described arrangements. The reduction in the device thickness contributes to a shrinkage of the space for incorporating the recording/reproducing device of the invention into an electronic appliance like, e.g., a computer. Especially when setting the device thickness to 20.5 mm or under, it is practical to mount two or more devices in a disposing space for a single unit of prior art device on the occasion of installing the recording/reproducing device of the invention instead of the existing recording/reproducing device the thickness of which is typically set to 41 mm as in a conventional 5-inch floppy disk drive. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the present invention will become apparent during the following discussion taken in conjunction with the reference drawings, in which: 
     FIG. 1 is a plan view illustrating a recording/reproducing device according to the present invention; 
     FIG. 2 is a plan view illustrating a state where the recording/reproducing device incorporates a jacket which accommodates a disk serving as a recording medium; 
     FIG. 3 is a partially cutaway exploded view in perspective, showing the recording/reproducing device of the invention; 
     FIG. 4 is a perspective view illustrating the jacket; 
     FIGS. 5 and 6 are partial schematic side elevations each showing an operation of a holder for holding the jacket; 
     FIGS. 7 through 9 are partial side views in vertical section, each showing an operation of an eject mechanism; 
     FIG. 10 is a plan view depicting a state where the jacket is mistakenly loaded; 
     FIG. 11 is a perspective view illustrating a head loading unit; 
     FIG. 12 is a sectional view depicting the head loading unit; 
     FIG. 13 is a plan view showing the recording/reproducing device when dismounting the holder; 
     FIG. 14 is an exploded perspective view showing heads, a carriage and a driving mechanism thereof; 
     FIG. 15 is a vertical sectional side view illustrating a geometry in which the heads and the carriage are disposed; 
     FIG. 16 is a vertical sectional side view illustrating a geometry in which a carriage driving motor is disposed; 
     FIG. 17 is a front elevation in vertical section, showing a geometry in which a control board and the carriage are disposed; 
     FIG. 18 is an exploded perspective view depicting a disk driving motor and a disk chucking mechanism; 
     FIG. 19 is a plan view of the chucking mechanism; 
     FIG. 20 is an enlarged sectional view taken substantially along the line A—A   20 — 20 of FIG. 19; 
     FIG. 21 is a sectional view showing a configuration in which a disk driving motor is disposed; 
     FIG. 22 is a perspective view showing a variant form of the chucking mechanism; 
     FIGS. 23 to  25  are sectional views each showing an operation of the chucking mechanism; 
     FIGS. 26 and 27 are plan views each showing a chucking action; 
     FIG. 28 is an enlarged plan view of the chucking mechanism; 
     FIGS. 29 through 32 are exploded perspective views each illustrating a configurational example where the recording/reproducing device of the invention is incorporated into an electronic appliance such as a computer; 
     FIGS. 33 to  35  are front elevations in vertical section, each illustrating a state where the recording/reproducing device of the invention is incorporated into the electronic appliance; 
     FIG.  38   36 is a front elevation thereof; 
     FIG. 37 is a perspective view, illustrating the electronic appliance equipped with the recording/reproducing device, of assistance in explaining the present invention; 
     FIG. 38 is a sectional view depicting a carriage unit in a conventional recording/reproducing device; 
     FIG. 39 is an enlarged view showing the principal portion thereof; 
     FIG. 40 is a plan view depicting a chucking mechanism of the prior art recording/reproducing device; 
     FIG. 41 is a bottom view thereof; 
     FIG. 42 is a vertical sectional view illustrating a disk driving motor equipped with a conventional chucking mechanism; 
     FIG. 43 is a enlarged view illustrating a driving pin unit thereof; 
     FIG. 44 is a vertical sectional view depicting a configuration in which a disk driving motor in another prior art example is disposed; 
     FIG. 45 is a plan view depicting a prior art recording/reproducing device; 
     FIGS. 46 and 47 are partial side elevations in vertical section, each showing an operation of an eject mechanism of the prior art recording/reproducing device; 
     FIG. 48 is an exploded perspective view showing a configuration in which the recording/reproducing device is incorporated into a conventional electronic appliance; and 
     FIG. 49 is a front elevation thereof. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A recording/reproducing device according to the present invention will hereinafter be described specifically with reference to the accompanying drawings. 
     Turning first to FIGS. 1 through 3, the numeral  1  represents a recoding/reproducing device. Designated at  2  is a device body frame formed to assume a box-like shape in which its upper and front surfaces are opened, and a central part of the bottom is formed with a circular opening  3  for installing a disk driving motor M 1  which will be mentioned later. For convenience, the explanation will be given in such a manner that front and rear direction of the device are indicated by arrows X 1  and X 2  in FIG. 3, right and left directions are indicated by arrows Y 1  and Y 2 , and up-and-down directions are shown by arrows Z 1  and Z 2 . 
     The frame  2  is adaptive to an installation in an unillustrated electronic appliance such as a computer through a pair of brackets  4  located right and left. The brackets  4  are fitted to the frame  1  by inserting unillustrated screws into fitting holes  4 a depicted in FIG.  3 . Internal thread holes generally indicated at  4 b are provided for fastening the electronic appliance with screws. 
     Attached to sides of the frame  2  on its front part, as depicted in FIG. 3, is a dressing plate  6  formed with an insertion port  6 a for a jacket J (illustrated in FIG. 4) for accommodating a disk D defined as a recording medium by use of a stopper hook  6 b provided integrally therewith. An inner surface of the dressing plate  6  is provided with a opening/closing shutter  7  for blockading the cartridge insertion hole  6 a. The shutter  7  is rotatably fitted thereto by inserting a support shaft  7 a into a hole bored in the frame  2 . The shutter  7  is constantly rotationally biased in such a direction as to close the insertion port  6 a with the aid of a torsion coil spring  9  secured to the support shaft  7 a. 
     As illustrated in FIG. 2, a holder  10  for accommodating and holding the jacket J is provided in an interior of the frame  2 . The holder  10 , as depicted in FIG. 3, assumes such a configuration that bilateral parts of a tabular member made of a metal are bent inwards in a substantially C-like shape. A substantially central front surface, exclusive of the bilateral parts, of the underside of the holder  10  is opened. When setting the jacket J in the holder  10 , the bilateral sides of the jacket J are inserted along inner surfaces of the C-like crooked parts. A dimension of the inner surface of the holder  10  is set substantially equal to a dimension of an external width of the jacket J. 
     Formed integral on the bilateral surfaces of the holder  10 , as illustrated in FIG. 3, are a pair of short cylindrical protrusions  10 a to which rollers  11  are so attached as to be rollable. Chased, on the other hand, in bilateral surfaces of the frame  2  are stepped guide grooves  12  for setting the holder  10  selectively in a jacket inserting/removing position and in a recording/reproducing position and holding it therein with the help of four pices  pieces of rollers mentioned above so as to correspond to these rollers  11 . Stretched between spring receivers  10 b provided on the bilateral surfaces of the holder  10  and spring receivers  4 c formed on the brackets  4 , as depicted in FIGS. 3 and 7, are tensile coil springs  13  for constantly biasing the holder  10  downwardly in a forward oblique direction of the Figures. With this arrangement, the rollers  1  of the holder  10  are, as shown in FIGS. 5 and 6, selectively fixedly positioned at angular parts of upper stepped portions  12 a or lower stepped portions  12 b of the stepped guide grooves  12 . 
     If the jacket J is not inserted into the holder  10 , the holder  10  is in the jacket inserting/removing position —i.e, the rollers  11  are, as depicted in FIG. 5, positioned at the angular parts of the upper stepped portions  12 a. The holder  10  is on the same level with the jacket insertion port  6 a of the dressing plate  6 , whereby the jacket J is insertable into the holder  10  via the insertion port  6 a. 
     In this state, the jacket J is set into holder  10  in an arrowed direction of FIG.  5  and is intruded inwardly of the frame. At this time, the holder  10  moves right together with the jacket J in FIG. 5, and subsequently the rollers  11  roll, as illustrated in FIG. 6, from the upper stepped portions  12 a to the lower stepped portions  12 b, with the result that the holder  10  comes to a predetermined recording/reproducing position, videlicet, the jacket j  J set in the holder  10  is positioned on a disk driving motor M 1  which will be described later. 
     Note that the respective rollers  11  are so fitted to the protrusions  10 a of the holder  10  as to be removable. The rollers having different diameters are selectively fitted thereto, thereby adjusting the level and position of the holder with respect to the frame  2 . 
     Mounted, as illustrated in FIGS. 1 and 2, on an upper surface of the holder  10  is a shutter releasing lever  15  for shifting a shutter J 1  of the jacket J to a release position by moving the shutter J 1  in an arrowed direction of FIG. 4 when inserting the jacket J. The shutter releasing lever  15  is rotatable by engaging an integrally formed fulcrum pin  15 a with a hole  18  shaped in a turnup piece  10 c of the holder  10 . Provided integrally at one end of the shutter releasing lever  15  is an operating protrusion  15 b, set downwards, for opening the shutter J 1  by engagement therewith. The operating protrusion  15 b, when inserting the jacket J into the holder  10 , acts to impinge upon an edge of the shutter J 1 , and the releasing lever  15  rotates anticlockwise in FIG. 1, thereby opening the shutter J 1 . Connected to the other end of the shutter releasing lever  15  is a return spring  17  of the lever  15 , the other end of which is in turn connected to a trigger  18  so secured to the holder  10  as to be rotatable about a shaft  18 a with the intention of constantly rotationally biasing the trigger  18  clockwise in FIG.  1 . 
     Fitted integrally to one end of the trigger  18  is a downward protrudent piece  18 b which, when mounting the jacket, impinges on an insertion-directional top end of the jacket J. As a result, the trigger  18  rotates anticlockwise in FIG. 1 resisting the return spring  17 . When ejecting the jacket, the protrudent piece  18 b and the shutter releasing lever  15  are rotated clockwise in FIG. 1 by a restoring force of the return spring  17 , thus moving the jacket in an ejecting direction. 
     A free end part  18 c of the other end of the trigger  18  is arranged to impinge, when inserting the jacket as shown in FIG. 2, on an inner surface  12 c on the rear side of the groove formed in the frame side surface and, when ejecting the jacket, on an oblique surface  12 d of a groove rear surface as shown in FIG. 1, thus preventing an unexpected movement of the holder  10  due to vibrations. 
     Mounted on the upper surface of the holder  10  is a lifter  20  for raising the holder  10  from the recording/reproducing position of FIG. 6 up to the jacket inserting/removing position of FIG.  5 . 
     The lifter  20  is, as depicted in FIG. 3, formed so  to assume such a configuration that both ends of an elongate tabular member made of a metal or the like are bent downward. Short cylindrical protrusions  209 a integrally shaped on both ends thereof are, as depicted in FIGS. 1 and 2, fitted in recessed grooves  21  formed in the frame side surfaces, thus providing a rotatable holding state. Referring to FIG. 1, the numeral  22  denotes an anti-removing screw penetrating one short cylindrical protrusion  20 a and screwed into the frame side surface, whereby the holder  10  is not removed upwards (on this side of the sheet in FIG. 1) when the device undergoes impulses from the outside. Note that the anti-removing screw may be omitted if a cover or the like is mounted on the upper surface of the device body. 
     As depicted in FIG. 3, rotary arms  320 b   20 b for moving up the holder  10  through the spring receivers  10 b provided on the holder  10  are shaped on both sides of the lifter  20 . An operating arm  20 c for rotating the lifter  20  about the protrusion  20 a is integrally provided downwardly of one of the rotary arms  20 b. The lifter  20  is, as illustrated in FIGS. 7 to  9 , arranged to rotationally operate with the aid of an eject arm engaging with the operating arm  20 c via a recess  23 a and of an eject button  24  fitted thereto. The eject button  24  is slidably inserted into a hole  6 c formed in the dressing plate  6 . It is to be noted that the eject button  24  is detachably attached to the eject arm  23  to facilitate the replacement thereof in the illustrative example but may be formed integrally with the eject arm  23 . 
     The lifter  20  is, when the holder  10  is in the jacket inserting/removing position shown in FIG. 5, brought into a state depicted in FIG. 7, while the eject button  24  is slightly retracted inside a hole  6 c of the dressing plate  6 . In the state of FIG. 7, a protrusion  20 d shaped on the lifter  20  loosely abuts against the spring receiver  10 b of the holder  10 , and hence the clockwise rotations of the lifter  20  in FIG. 7 are hindered. 
     In the state OF  of FIG. 7, when inserting the jacket J from the jacket insertion port  6 a of the dressing plate  6  into the interior of the holder  10 , the top of the jacket J impinges upon a stopper  10 d provided at the rear end of the holder  10 . In the case of effecting further intrusion, the jacket J is inserted together with the holder  10  into the device body frame  2 , thus setting it in the recording/reproducing position depicted in FIG.  8 . At this time, the lifter  20  rotates clockwise in FIG.  7  through the spring receiver  10 b. Concomitantly with the rotation of the lifter  20 , the eject button  24  is, as illustrated in FIG. 8, protruded forwardly of the dressing plate  6  through the operating arm  20 c and the eject arm  23 . 
     A recording/reproducing operation is performed in such a state. When depressing the eject button  24  on finishing that operation, the lifter  20  rotates anticlockwise in FIG. 8 with the help of the eject arm  23  and the operating arm  20 c. The holder  10  is raised by the rotary arm  20 b of the lifter  20  through the spring receiver  10 b and then reverts to the jacket inserting/removing position of FIG.  7 . In the illustrative example, at that time the spring receiver  10 b formed in the holder  10  is set slightly forward so that, as shown in FIG. 9, the rear part of the holder  10  is raised ahead and collides with the stopper  25  provided on the frame side surface. Thereafter, the holder reverts to the state depicted in FIG. 7 by depressing the eject button  24 . However, another practical arrangement is that the priority of lifting is given to the front part of the holder  10 , or alternatively the front and rear parts thereof can be raised in parallel by changing a position of the spring receiver  10 b. 
     The description will next be focused on a lock process if the holder  10  makes unexpected actions. The unexpected actions imply that the jacket J is mistakenly inserted, or the holder  10  slides before the shutter J 1  of the jacket J opens, or the shutter J 1  does not open. Turning to FIG. 10, if the jacket is inserted in an arrowed direction f in such a-state  a state that its upper and lower surfaces or front and rear parts are reversed, the insertion-directional top end of the jacket J collides with the operating protrusion  15 b of the shutter releasing lever  15 , whereby the lever  15  slightly rotates anticlockwise in FIG.  10 . When further inserting the jacket, a lock pin  15 c provided on the shutter releasing lever  15  impinges on a turnup piece  10 e defined as a part of the holder  10  before abutting against the downward protrudent  protruding piece  18 b of the trigger  18 . Subsequently, the holder  10  slightly slides in the arrowed direction f resisting the biasing force of the spring  18 , and eventually the free end part  18 c of the trigger  18  mounted on the holder  10  impinges upon the oblique surface  12 d formed on the frame  2 , thereby hindering the holder  10  from sliding in the arrowed direction a  f. Thus, there is developed a state where the jacket can not be inserted any more. With this arrangement, the rollers  11  of the holder  10  do not come off the upper stepped portions  12 a depicted in FIG. 5, and it follows that the installation in the recording/reproducing position shown in FIG. 6 is not attained. Even if the holder  10  slides in the arrowed direction f by dint of any outside force without causing oscillations of the shutter releasing lever  15 , the holder  10  is not set by the above-mentioned operations. It is therefore possible to prevent damages to the components incorporated into the device. 
     A head load mechanism will next be described. An upper head  40  and an upper carriage  41  for holding the head  40  are, as shown in FIGS. 1 and 11, located in rear of the holder  10 . Mounted on a rear upper surface of the holder  10  is a head load arm  30  for, as illustrated in FIGS. 1,  3 ,  11  and  12 , retreating upwards the upper head  40 , interlocking with the lifting operation of the holder  10 . Note that a lower head  50  and a lower carriage  51  which will hereinafter be explained are provided under the upper head  40  and the upper carriage.  
     The head load arm  30  is, as shown in FIGS. 3 and 12, so mounted as to be vertically rotatable by engaging a pair of protrusions  30 a integral with the arm  30  with engaging holes  31 a formed in a pair of erect pieces  31  on the holder upper surface. The head load arm  30  is kept on a predetermined level by impinging, on the holder upper surface, a lower end of an adjusting screw  32  screwed into a nearly central part of the head load arm  30 . Designated at  33  is a torsion coil spring for constantly rotationally biasing the head load arm  30  in such a direction as to impinge upon the holder upper surface. 
     In a state where the jacket J inserted in the holder  10  is set in the recording/reproducing position, the holder  10  is situated in a position indicated by a solid line of FIG.  12 . In this state, when ejecting the jacket J, as discussed above, the holder  10  ascends, and correspondingly the hear  head load arm  30  also moves upwards in parallel in the manner indicated by a dotted line of FIG.  12 . This action permits a free end part  30 b of the head load arm  30  to engage with a raising member  41 a of the upper carriage  41 , thereby raising the upper head  40  together with the upper carriage  41 . A predetermined clearance between the upper head  40  and the jacket J is thus secured. It is to be noted that, even if there is caused a scatter in height of the holder  10 , it is feasible to properly adjust the clearance by moving the free end part  30 b of the head load arm  30  up and down in the Figure. There may be, if necessary, provided an eccentric pin  34 , depicted in FIGS. 1 and 3, for adjusting the free end part  30 b of the head load arm  30  to have parallelism. 
     As depicted in FIG. 1, a damper  35  is disposed aside of the head load arm  30 . The damper  35  is constructed such that a damper arm  35 a thereof engages with a segment  30 c of the head load arm  30 . The damper  35  behaves to prevent an intensive impingement of the upper head  40  upon the disk D when setting the jacket in the recording/reproducing position. 
     Constructions of the upper and lower heads  40  and  50  and also the carriages  41  and  51  will be explained in conjunction with FIGS. 13 to  16  inclusive. 
     The upper carriage  41  for holding the upper head  40  is, as illustrated in FIGS. 4 and 15, located on the lower carriage  51  for holding the lower head  50 . The lower carriage  51  is moved along a carriage guide shaft  60  by means of a stepping motor M 2  serving as a carriage driving motor, thereby setting the upper and lower heads  40  and  50  in such positions as to move in the radial direction with respect to the disk set in the recording/reproducing position. 
     A bearing member  51 a for the guide shaft  60 is , as illustrated in FIG. 15, is integrally provided on the underside of the lower carriage  51 . A sintering  sintered metal  85   65 for movably guiding the lower carriage  51  is press-fitted in the bearing member  51 a. Fixed to a recess  51 b, shown in FIG. 14, of the lower carriage  51  by bonding is a lead pin  62  for engagement-tracing the groove of a lead screw  61  attached to the stepping motor M 2 . A lead pin pressurizing spring  63  is fitted in an internal thread hole  51 c of the lower carriage  51  with a screw  64  so that the lead pin  62  exactly traces the groove of the lead screw  61  by pressurizing the lead pin  62 . Provided on the lower carriage  51  is a stopper  51 d for preventing the lead pin  62  from coming off the groove of the lead screw  61  when an impulsive force is exerted thereon. Bonded fixedly to the top end of the lower carriage  51  are a shield plate  52  for shielding a magnetic leakage from the disk driving motor M 1  which will be mentioned later and a lower head  50  for recording and reproducing signals on and from the disk in such a manner that the shield plate  52  and the lower head are attached to a gimbal composed of a leaf spring to have a gimbal structure for keeping the head and the disk in a well-contacted state. Movably attached to a part of the lower carriage  51  is a 00 shutter  53  for blockading a photo sensor (not illustrated) for detecting the fact that the lower carriage  51  moves to a reference position, the shutter  53  being movable in an arrowed direction g in FIG.  14 . 
     An upper head  40  fitted to an upper gimbal  40 a is, as in the case of the lower head  50 , bonded to the upper carriage  41 . The upper carriage  41  includes a pair of fulcrum members  41 b serving as a rotary fulcrum in order to raise the raising member  41 a by use of the head load arm  30  when setting or ejecting the jacket J. The upper carriage  41  is attached to the lower carriage  51  through a suspension  42  formed of a lead spring. The numeral  43  represents a suspension holder; and  44  a fitting screw screwed into an internal thread hole  51 f of the lower carriage  51 . 
     Stretched between a spring catching member  51 e of the lower carriage  51  and another spring catching member  41 c of the upper carriage  41  is a head load spring  54  for pressurizing the lower and upper heads  50  and  40  to obtain a contact pressure with the disk. Three catching positions are provided particularly for the spring catching member  41 c of the upper carriage  41 , thus giving s structure capable of subtly adjusting the pressure acting on the head. A position of the head load spring is set in an interior of a triangle region defined by the raising member  41 a of the upper head  40  and the pair of fulcrum members  41 b, as a result of which the upper carriage can horizontally be raised with no inclination even when lifting only one portion of the raising member  41 b. When exerting the impulses in a state where the upper carriage  41  is raised by the raising member  41 a, the top end of the upper carriage  41  is lowered, and at the same moment the fulcrum members  41 b float. In an extreme case, the lower head  50  collides with the upper head  40 , and, it can be considered, these heads are thereby broken. For this reason, a holder member  43 a for the fulcrum members  41 b of the upper carriage  41  is shaped on the suspension holder  43  in order to prevent floating of the fulcrum members  41 b, thereby improving anti-impulse properties. Led from the upper and lower heads  40  and  50  are flexible printed boards  40 b and  50 b for connecting the heads to a control circuit, the thicknesses of which are small. This causes a decline in handling property, and hence grooves  51 g are chased in the lower carriage  51  for guiding them. 
     Explaining the flexible printed board  50 b catered for the lower head, a crank member  51 h of  is provided on the lower carriage  51  to hold the flexible printed board  50 h   50 b. 
     The flexible printed board  40 b for the upper head is arranged such that the board  40 b is guided by the catching member  41 d of the upper carriage  41 , thus keeping the flexible printed board  40 b in a predetermined configuration. 
     The carriage guide shaft  60  is secured to the frame  2  from the underside (from the same direction as the fitting surface of the disk driving motor which will be described later) by use of a clamp  66  with a screw  67 . 
     The stepping motor M 2  for effecting a movement-positioning process of the carriage in the radial direction of the disk along the guide shaft  60  rotates through an angle of 18 degrees by one step. The lead screw  61  is guided by a pivot bearing  68  whose top end is fitted to the frame  2  and by a metal bearing  69  whose central part is likewise fitted to the frame  2 , the lead screw  61  undergoing forces acting both in a thrust direction and in a radial direction. Balls  70  and  71  each having a high hardness are embedded into front and rear ends of the lead screw  61 , thus ameliorating an abrasion resistant property. 
     A rotor magnet  72  of the stepping motor M 2  is fixedly bonded to the lead screw  61 . The rotor magnet  72  involves the use of neodymium ferrous boron. Sufficient torque is obtained even when reducing the diameter thereof because of a large magnetic force. Thus, the stepping motor is miniaturized. A thrust spring  73  for imparting a thrust-directional pressure to the lead screw  61  is set at the rear end of the stepping motor  2 , and a motor cap  74  undergoes a thrust force. Disposed outwardly of the stepping motor M 2  is a motor clamp  75  whose spring property acts to fix the stepping motor to the frame  2 . 
     Based on this construction, it is a common practice that the carriage position is adjusted while rotating the stepping motor M 2 . The lead screw  61  rotates with revolutions of the stepping motor M 2 . The lead pin  62  engaging with the lead screw groove moves to adjust a position of the carriage. A contact portion between the motor clamp  75  and the motor M 2  is formed to be a projection  75 a. This arrangement facilitates both revolutions of the stepping motor M 2  and the adjustment. Besides, a flange  76  of the stepping motor M 2  is toothed to facilitate adjustment by a jig and automatization as well. 
     Note that centering of the stepping motor is effected by engaging the metal bearing  69  fitted to the frame  2  with the flange  76  of the stepping motor 
     Next, as illustrated in FIGS. 13 and 17, a control board  80  flush with the carriage  51  is fixed to the frame  2  with a screw. The control board  80  and the carriage guide shaft  60  are, as depicted in FIG. 13, disposed with some deviation on the plane, thus making the device thin so that the carriages  41  and  51  can be disposed as low as possible. The control board  80  is partly overlapped with the carriage  51 . More specifically, as illustrated in FIG. 17, for the purpose of avoiding the entire superposition on the carriage  51 , a part  80 a having a large height on the control board  80  and a part  80 b having a small height are overlapped with a part of the carriage  51 . Fundamentally, overlapping of the control board  80  with the carriage  51  is prevented in the thicknesswise direction (up-and-down direction in FIG.  17 ). 
     A disk chucking mechanism for chucking the disk and a disk driving motor for rotationally driving the disk will next be explained with reference to FIGS. 13 and 18 through  21 . 
     A disk driving motor M 1  in this embodiment involves the use of a spindle motor for performing a direct drive, . The motor M 1  is supported on a motor board  81  into which the motor control board is packaged. The board  81  is mounted on the frame  2 , whereby the motor M 1  is, as shown in FIG. 13, located within the opening  3  of the frame  2 . Mounted on the motor board  81  are detecting switches  82 a and  82 b for detecting that the jacket J has, as illustrated in FIG. 18, been set in the recording/reproducing position or detecting a condition of the jacket J and also a connector  88   83 for mounting LEDs for displaying operations of the recording/reproducing device. A housing  84  and a stator  85  wound with a coil are disposed at the center of the motor board  81  and fixed with a nut plate and three pieces of countersunk screws while these components are sandwiched therebetween. 
     A ball bearing  89  is, after press-fitting the metal bearing  88 , bonded to the housing  84 . A rotor magnet (driving magnet) disposed vis-a-vis with the stator  85  is fixedly bonded to these bearings  88  and  89 . A rotor  90  is constructed by simultaneously forming a detecting magnet  93  for detecting the number of revolutions of the motor M 1 , a chucking magnet  94  for attraction-positioning the hub H of the disk D and a rotary driving shaft  91  by use of plastic magnets. The rotary driving shaft  91  of the rotor  90  is inserted through a spacer  95  for adjusting an axial position. The  A rotor magnet  92  is composed of a rare earth group high performance magnet, which leads to radial and axial miniaturization and a reduction in thickness of the rotor magnet  92  itself and further of the disk driving motor M 1 . 
     Fixedly formed on the upper surface of the rotor  90  is the chucking magnet  94  which is in turn formed with a circular-arc opening  94 a through which the rotor surface is partly observed. Provided in this opening  94 a are a fulcrum hole  90 a constituting a rotary fulcrum of the chucking lever  96  by engaging with a burring-machined fulcrum shaft member  96 a fitted to the chucking lever  96  for centering and rotationally driving the hub H while engaging with a driving hole h 2  of the hub H and also a caulking hole  90 b for fixedly caulking the level pin  97  for guiding the chucking lever  96  and for fitting it to the rotor  90 . Besides, a slide sheet  98 , made of a material exhibiting a good sliding property, for receiving the hub H is stuck to the upper surface of the chucking magnet  94 . A screw generally indicated at  81 a is intended to secure the motor board  81  to the frame  2 . In the illustrative example, the motor board  81  is fixed from underside of the frame  2  with three pieces of countersunk screws  81 a. 
     Referring to FIG. 19, a portion, marked with a multiplicity of points in the Figure, of the chucking magnet  94  is magnetized to assume such a configuration that adsorptive forces of the hub H become uniform with respect to the center of the rotary driving shaft  91 . As illustrated in FIGS. 19 and 20,  21  and  22  a diameter of the guide hole  96 b of the chucking lever  96  is slightly larger than a guide diameter  97 a of the lever pin  97 , whereby the chucking lever  96  is allowed-to make a necessary amount of movement in an arrowed direction j in FIG.  19 . On the other hand, a permissible movement in an arrowed direction k of FIG. 20 is limited to a small clearance between the lever pin  97  and the chucking lever  96 , thus providing a structure in which the burring-machined fulcrum shaft member  96 a fitted to the chucking lever  96  does not disengage from the fulcrum hole  90 a for constituting the rotary fulcrum of the chucking lever  96 . 
     On the basis of this constitution, the hub H is, as depicted in FIG. 20, adsorbed onto the slide sheet  98  by dint of the chucking magnet  94 ; and the hub H is positioned both in the rotational direction and in the radial direction while being engaged by, as illustrated in FIG. 19, tuning a position of the driving hole h 2  of the hub H to the chucking lever  96 . In this case, the driving hole h 1  of the hub H is not initially matched with the position of the chucking lever, and it follows that the hub H is a little bit slant. However, the chucking lever  96  is aligned with the driving hole h 2  of the hub H by the revolutions of the motor M 1 , and then the hub H is set in the position depicted in FIG.  20 . It has proven to be most preferable from an experiment to set an engagement quantity  11  of the chucking lever of FIG. 20 with the hub H to 0.78 mm or less in order to reduce the inclination of the hub H and effect the stable chucking process. 
     An upper surface  90 c of the rotor  90  of the motor M 1  is, as illustrated in FIG. 21, substantially flush with an upper surface  2 d of the frame  2  but is set somewhat lower than this, thereby preventing interference with the jacket J which accommodates the disk D. 
     Furthermore, as shown in FIG. 21, the bearing unit of the motor M 1 hahas such a construction that the rotary driving shaft  91  fixed to the rotor  90  is inserted into a central hole penetrating the metal bearing  88  and the ball bearing  89 . Based on this construction, when, for instance, large impulses are applied from the outside, there exists a probability that the rotary driving shaft  91  moves upwards in the Figure, i.e., in a direction opposite to the motor board  81 . For this reason, the speed detecting magnet  93  provided on the outer peripheral surface of the rotor is formed larger than the hole diameter of the opening  3  of the frame  2 . Owing to this arrangement, when undergoing the impulses, and even when the rotor  90  moves upward in the Figure, the speed detecting magnet  93  impinges on the circumference of the opening  3 , thereby preventing the removable  removal of the rotary driving shaft  91  and the rotor  90 . 
     At lest  least the lower carriage  51 is disposed ionin the radial direction outwardly of an outer shape of the rotor  90 Ofof the motor M 1 . Even when the carriage  51  moves to the innermost periphery of the disk D, the superposition of the rotor  90  on the carriage  51  in the thicknesswise direction (up-and-down direction in FIG. 21) is prevented. Particularly in the illustrative embodiment, the outer shape of the rotor  90  has a diameter of 38 mm, while the top end of the carriage  51  when moving farthest toward the rotor is positioned 19.5 mm away from the center of the motor M 1 , which eliminates the interference of the rotor  90  with the carriage  51 . 
     Note that an outer shape of the speed detecting magnet  93  has a diameter of  42  mm. The magnet  93  is partly overlapped with the carriage  51  in the thicknesswise direction. However, the speed detecting magnet  93  is formed small in the thicknesswise direction. This arrangement, as in the case of partial overlapping of the control board  80  with the carriage  51  in FIG. 17, does not exert an influence in the thicknesswise direction of the recording/reproducing device. Consequently, a thickness ranging from the lower surface of the motor board  81  to the rotor upper surface can be reduced down to 6 mm in this embodiment. 
     A factor for determining the thickness of the actual recording/reproducing device as a whole will be given as follows. The hub H fitted with the disk is, as depicted in FIGS. 18 and 20, adsorbed onto the motor M 1 , and in order to obtain, as shown in FIG. 15, a well-contacted state there is disposed the upper head the recording/reproducing surface of which is substantially flush with the disk. The upper carriage  41  for supporting the upper head  40  is further provided. For taking the jacket accommodating the disk is taken  out of the recording/reproducing device,.the  device, the upper head  40  is raised a distance equivalent to the  half of the thickness of the jacket J to steer clear of the jacket J. 
     A thickness of the motor M 1  is, as explained earlier, set to 6 mm; a thickness of the chucking unit is 0.8 mm; a height from the hub H to the disk surface is approximately 1.4 mm; and a thickness of the jacket J is 3.3 mm (the set values are all reported on America  American National Standard X3B8-84-201). The upper head  40 , which has already been standardized in the industrial field fro  for use with the flexible disk drive unit, is set to 2.7 mm. The upper head  40  of the upper carriage  41  needs to be spaced at least 0.5 mm enough to provide a shape  away from the disk jacket J to prevent the head from being damaged or destroyed when inserting or removing the jacket J. 
     Hence, the details of the minimum necessary thickness of the entire device are such that: a thickness of the motor M 1  is 6 mm; a thickness of the chucking unit is 0.8 mm; a thickness of the disk is 1.4 mm; a half thickness of the jacket is 1.65 mm; a thickness of the upper head is 2.7 mm; and a thickness of the upper carriage is 0.5 mm. The device thickness is totally 13.55 mm. 
     In fact, however, tolerances of the respective components are produced, and therefore the clearance is required to be eliminated for preventing the interference. Since a shield or the like for preventing noises given from the outside is added, the thickness of the whole device can be set to approximately 16 mm. As a matter of fact, much the same thickness can be attained in this embodiment. 
     Turning to FIGS. 22 through 28, there are illustrated variant forms of the chucking mechanism, wherein the components having the identical functions are marked with the  like symbols, and the explanatory repetition is therefore omitted herein. 
     One end of the chucking lever  96  is, as shown in FIG. 22, rotatably fixed to the rotor  90  with a chucking lever pin  99 a. A driving pin  99 b is fixed to a free end of the chucking lever  96  by caulking. The chucking lever  96  is disposed in an opening  94 a formed in the chucking magnet  94 , and the rotor upper surface is formed with an opening corresponding to the opening  94 a. 
     In a state where the disk D is not loaded on the rotor, as illustrated in FIG. 23, the driving pin  99 b is protruded upwardly of a slide sheet  98 . In this state, when the hub H of the disk D is adsorptively held onto the slide sheet  98  by the chucking magnet  94 , ordinarily the driving pin  99 b is pushed by the hub H and moves down due to deflection of the chucking lever  96  because of a small probability that the driving hole h 2  of the hub H does not coincide with the position of the driving pin  99 b. Note that the chucking lever  96  in this embodiment involves the use of a spring plate having a thickness of approximately 0.15 mm. 
     Subsequently, when the rotor  90  rotates in response to a motor driving signal, the driving hole h 2  of the hub H is aligned with the driving pin  99 b, and, as illustrated in FIG. 25, the driving pin  99 b is protruded into the driving hole h 2  by a restoring force of the chucking lever  96 . 
     Besides, the driving pin  99 b impinges and immediately engages with two surfaces h 2 a and h 2 b of the driving hole h 2 , with the result that the chucking lever  96  is rotationally moved in an arrowed direction m in the Figure  FIG. 26by the disk rotary force. Then, two surfaces h 1 a and h 1 b of a central hole h 1  of the hub H are pushed against the rotary driving shaft  91 , thus centering the hub H (FIG.  27 ). 
     It is to be noted that a rotary range of the chucking lever  96  is, as shown in FIG. 28, regulated by the rotor and by inner wall surfaces  94 a  1   94 a 1 and  94 a  2   94 a 2 standing vis-a-vis with each other in the radial direction of the circular arc opening  94 a formed in the chucking magnet  94  to effect an exact engagement of the driving pin  99 b with the driving hole h 2 . The chucking lever pin  99 a, as depicted in FIG. 23, behaves to hold the chucking lever  96  while keeping the clearance of smaller than 0.1 mm to regulate the up-and-down motions of the chucking lever  96  in the Figure. A protrusion quantity  distance  12  of the driving pin  99 b from an upper surface of the slide sheet  98  is set lower than a thickness  13  obtained by adding thicknesses of the rotor  90 , the chucking magnet  94  and the slide sheet  98 . With this arrangement, when performing the chucking operation, the chucking lever is, as illustrated in FIG. 24, not protruded into the rotor  90 . In addition, a sliding force of the driving pin  99 b on the hub H can be decreased. It is also possible to reduce both the thickness of the chucking mechanism and a degree of defacing between the hub H and the driving pin  99 b during the chucking operation. 
     Hence, as in the previous example, the motor M 1  can be decreased in thickness similarly in the embodiment of FIGS. 22 to  28 , which in turn leads to a reduction in thickness of the recording/reproducing device as a whole. 
     As discussed above, since the respective components of the recording/reproducing device have the above-mentioned constitutions, the thickness of the entire device can be set to at least 20.5 mm or under. Especially in the foregoing embodiment, the thickness can, as stated earlier, be reduced down to about 16 mm. This reduction conduces to a remarkable decrease in space for incorporating the device in an electronic appliance like, e.g., a computer. 
     As described above, the arrangement that the device thickness is set to less than 20.5 mm makes the following placement geometries practicable in the case of mounting the recording/reproducing device  1  of the present invention in the electronic appliance such as a computer or the like. 
     FIGS. 29 to  37  show configurations in which the recording/reproducing device  1  based on the above-mentioned floppy disk drive (FDD) serving as an external storage unit is incorporated into a computer-based electronic appliance. 
     Referring to FIGS. 29 through 32 and  36 , an external storage unit  101  of the electronic appliance is constructed in the following manner. Two sets of recording/reproducing devices  1  each employing, for example, a miniaturized 3.5-inch FDD are mounted in a chassis  102  made by machining, e.g., a steel sheet to have the same size and fitting structure as those of a chassis of, e.g., a conventionally used 5-inch FDD. Attached to the front surface of the chassis  102  is a front bezel  104  having almost the same size as that of, e.g., the 5-inch FDD and formed with insertion ports  104 a (illustration is omitted in FIGS. 29 through 32) for mounting 3.5-inch disks, corresponding to two sets of recording/reproducing devices  1 . 
     Turning to FIG. 36, the front bezel  104  includes a recess  104 b suitable for inserting and removing the 3.5-inch disk, the recess  104 b being formed substantially in the vicinity of the insertion port  104 a. There are also equipped a button  118  for ejecting the 3.5-inch disk and an LED  117  for displaying working conditions of the recording/reproducing device  1 . 
     A structure of attaching the front bezel  104  to the front surface of the chassis  102  entails the steps of firstly shaping a fixing member  104 b on the front bezel  104  to fix the front bezel  104 to   104  to a bottom surface of the chassis  102  formed to assume a substantially U-like shape, forming key-like engaging members  102 b, provided at upper ends of both side surfaces of the chassis  102 , for sustaining the front bezel  104  so as not to be inclined forward, providing hook members  104 c engaging with the engaging members  102 b on the front bezel  104 , engaging the engaging members  102 b with the hook members  104 c, and finally fixing the front bezel  104  to the bottom surface of the chassis  102  with screws  119 . 
     A specific structure of incorporating two sets of recording/reproducing devices  1  into the chassis  102  will be mentioned in greater detail. Substantially perpendicular side walls  102   a  serving as a part of the chassis  102  are formed on a part of both side surfaces of the recording/reproducing device  1  and then fixed thereto with a plurality of screws  106 . 
     Located in  at a rear of the recording/reproducing device  1  is a relay board invested with an interface function identical with that of, e.g., the 5-inch FDD, this function being different from a commonly used interface function which is standardized for use with a 3.5-inch recording/reproducing device. 
     The relay board works differently in accordance with contents shown in FIGS. 29 through 32. The contents will be explained respectively. 
     (1) A relay board  105  depicted in FIG. 29 includes: a card edge connector  107 , connected to a host-side connector, for receiving and transferring signals; a power supply connector  108  supplied with electric power; connectors  109  connected to each of two sets of recording/reproducing devices  1 , for receiving and transferring the signals, and also provided at an end of a flat cable  110 ; and two pieces of poser  power supply terminals  111 , connected to each of two sets of recording/reproducing devices  1 , for supplying the electric power. The relay board  105  is fixed to the chassis  102  with screws  113 . 
     The relay board  105  is equipped with a driving element  112  for increasing a current driving ability of an output signal of the 3.5-inch recording/reproducing device  1  up to a current value of the 5-inch FDD. The relay board  105  also has, e.g., a plurality of short plugs  114  as selective setting means for selectively setting a driving state of the 3.5-inch recording/reproducing device  1  or selectively setting the specifications thereof. 
     (2) A different arrangement of a relay board  105 A depicted ion FIG. 30 from the relay board  105  of FIG. 29 is that there are not provided two pieces of power supply terminals  11 , connected to each of two sets of recording/reproducing devices  1  shown in FIG. 29, for supplying the electric power, and instead, the electric power is supplied via two pieces of connectors  109  disposed at the end of the flat cable  110 . 
     Other constructions are the same as those shown in FIG.  29 . The relay board  105 A includes: the card edge connector  107 , connected to the host-side connector, for receiving and transferring the signals; the power supply connector  108  supplied with the electric power; and two pieces of connectors  109 , connected to each of two sets of recording/reproducing devices  1 , for receiving and transferring the signals, and located at the end of the flat cable  110  for supplying the electric power. The relay board  105 A is fixed to the chassis  102  with the screws  113 . 
     The relay board  105 A is equipped with the driving element  112  for increasing a current driving ability of an output signal of the 3.5-inch recording/reproducing device  1  up to a current value of the 5-inch FDD. The relay board  105 A also has, e.g., a plurality of short plugs  11 A   114 as selective setting means for selectively setting a driving state of the 3.5-inch recording/reproducing device  1  or selectively setting the specifications thereof. 
     (3) A big difference between a relay board  115  shown in FIG.  31  and the relay boards  108  and  105 A depicted in FIGS. 29 and 30 is that two sheets of relay boards  114  are provided corresponding to two sets of recording/reproducing devices  1 . Other constructions are the same as those shown in FIG.  29 . Each of the two relay boards  115  depicted ion FIG. 31 has: the card edge connector  107 , connected to the host-side connector, for receiving and transferring the signals; the power supply connector  108  supplied with the electric power; the connectors  109 , connected to each of the two recording/reproducing devices  1 , for receiving and transferring the signals, and located at the end of the flat cable  110 ; and power supply terminals  111 , connected to the recording/reproducing devices  1 , for supplying the electric power. Set between the relay boards  115  is a bush  118  which is in turn fixed to the chassis  102  with the screws  113 . 
     Each of the relay boards  115  is equipped with the driving element  112  for increasing a current driving ability of an output signal of the 3.5-inch recording/reproducing device  1  up to a current value of the 5-inch FDD. The relay board  115  also has, e.g., a plurality of short plugs  114  as selective setting means for selectively setting a driving state of the 3.5-inch recording/reproducing device  1  or selectively setting the specifications thereof. 
     (4) A different arrangement of the relay board  115 A depicted in FIG. 32 from the relay board  115  of FIG. 31 is that there are not provided the power supply terminals  111 , connected to the recording/reproducing devices  1  shown in FIG.  51   31 , for supplying the electric power, and instead, the electric power is supplied via the connectors  109  disposed at the end of the flat cable  110 . 
     Other constructions are the same as those shown in FIG.  31 . The relay board  115 A includes: the card edge connector  107 , connected to the host-side connector, for receiving and transferring the signals; the power supply connector  108  supplied with the electric power; and the connectors  109 , connected to each of two sets of recording/reproducing devices  1 , for receiving and transferring the signals, and located at the end of the flat cable  110  for supplying the electric power. Set between the relay boards  115 A is the bush  118  which is fixed to the chassis  102  with the screws  113 . 
     The relay board  115 A is equipped with the driving element  112  for increasing a current driving ability of an output signal of the 3.5-inch recording/reproducing device  1  up to a current value of the 5-inch FDD. The relay board  115 A also has, e.g., a plurality of short plugs  114  as selective setting means for selectively setting a driving state of the 3.5-inch recording/reproducing device  1  or selectively setting the specifications thereof. 
     Next, a structure of fixing the 3.5-inch recording/reproducing device  1  to the chassis  102  will be explained in conjunction with FIGS. 33 to  35 . Referring to FIGS. 33 through 35, the chassis  102  constructed by machining, e.g., a steel sheet to have almost the same size and fitting structure as those of the chassis of the 5-inch FDD is formed inside with nearly perpendicular side walls  102   a  shaped by effecting, e.g., a bending process so as to substantially match with the side surfaces of the recording/reproducing device  1 . Two sets of miniaturized 3.5-inch recording/reproducing devices  1  are installed between the side walls  102   a  and then fixed thereto with a plurality of screws  106 . 
     Turning attention to a relationship between the chassis  102  and the two 3.5-inch recording/reproducing devices  1  incorporated between the side walls  102   a,  a bottom surface  102   c  of the chassis  102  almost accords with a bottom surface  1   b  of the recording/reproducing device  1  in FIG.  33  and the two 3.5-inch recording/reproducing devices  1  are so mounted as to be superposed on each other. 
     On the other hand, turning to FIG. 34, the recording/reproducing device  1  disposed inwardly of the chassis  102 . The bottom surface  102   c  of the chassis  102  deviates by a thickness of the chassis  102  from the bottom surface  1   b  of the recording/reproducing device  1 . Two sets of 3.5-inch recording/reproducing devices  1  are so installed as to be superposed on each other. 
     Referring to FIG. 35, the recording/reproducing devices  1  are, as in the case of FIG. 34, disposed inwardly of the chassis  102 . Formed between the two 3.5-inch recording/reproducing devices  1  is a space  1   a  by which to prevent deteriorations of the recording/reproducing devices which are caused by interactions of noises of magnetic and electric fields generated by the two recording/reproducing devices  1  or resonances derived from interactions of working sounds of both of the recording/reproducing devices  1  even under an excessively dense state of placement. 
     Note that the structures, shown in FIGS. 33 to  35 , of fixing the 3.5-inch recording/reproducing devices  1  to the chassis  102  are different from each other but do not present essential difference in terms of their recording/reproducing functions. 
     On the basis of such a construction, for instance, a 5-inch FDD is completely replaceable with the recording/reproducing device  1  of the present invention in a variety of electronic appliances each loaded with the 5-inch FDD. 
     Next, constitutional characteristics of the above-mentioned embodiment will be given as follows: 
     1) The number of recording/reproducing devices incorporated 
     In the foregoing embodiment, there are installed two sets of 3.5-inch recording/reproducing r  devices  1 , and two pieces of respective relay boards  105 ,  105 A,  115  and  115 A. The front bezel  104  is formed with the insertion ports  104   a  for mounting the 3.5-inch disks, corresponding to the two recording/reproducing devices  1 . As a matter of course, however, the number of the devices is not limited to two. The gist of the embodiment can also be attained by providing these components singly. 
     2) Thickness of recording/reproducing device 
     As stated before, the recording/reproducing devices such as FDDs, HDDs, ODDs and tape streamers which have widely been spread as external storage units of multiple computer-based electronic appliances are substantially standardized in their sizes of outer shapes and fitting dimensions thereof depending on sizes of the recording mediums. The standardization has been carried out on the basis of the FDDs. Under such circumstances, the description in this embodiment has been developed so far by exemplifying the FDD for explanatory convenience. 
     Now, a descriptive emphasis will be placed on the contents of standardization. 
     The competitors have expanded their technical activities aiming at a reduction in the device thickness from an early stage at which the FDDs came out on the market. As a result, a dominant type of FDDs of nowadays are 5-inch FDDs each having a thickness 41 mm and 3.5-inch FDDs each having a thickness of 28.5 mm (1 inch) . These FDDs are interchangeable with respect to the recording/reproducing operations. 
     While on the other hand, the current tendency for more miniaturized and thinner devices is giving an acceleration to the technology wherein the most popular FDDs having the device thickness of 25.4 mm (1 inch) will be developed into FDDs having a mechanism thickness of 12.7 mm (½ inch) that is one-half the former. This is a big target among the competitors. 
     In accordance with the embodiment of the invention, however, the mechanism thickness is set from another point of view. The present invention aims at incorporating two sets of 3.5-inch recording/reproducing devices into the same space as that of the 5-inch FDD having a device thickness of 41 mm which is now spread over most widely. In the structure of mounting the 3.5-inch recording/reproducing devices depicted in FIGS. 33 to  35 , these devices are not limited to unitized devices such as the FDDs. If preferably unitized, it is convenient to handle the FDD as one unit even when separating it from the chassis  102 . 
     When mounting two sets of 3.5-inch recording/reproducing devices in the chassis  102  having the same thickness as a device thickness, 41 mm, of the most popular 5-inch FDD, in the fitting structure shown in FIG. 33, a preferable thickness of the 3.5-inch recording/reproducing device is approximately 20.5 mm. In the fitting structure depicted in FIG. 34, a thickness of the chassis  102  is set to approximately 4 mm, and if some scatter is to be considered, a preferable thickness of the 3.5-inch recording/reproducing device is about 18 mm. 
     In the fitting structure illustrated in FIG. 35, if the space  1   a  is formed as large as possible, there are, as a matter of course, reduced the influences exerted by noises of the foregoing electric and magnetic fields and by operating sounds. Supposing herein that there exists, more or less, scatter by setting the space  1   a  to, e.g., 4 mm or thereabouts and the thickness of the chassis  102  to approximately 2 mm, a preferable thickness of the 3.5-inch recording/reproducing device is approximately 17 mm. 
     Note that there may be prepared, though not illustrated in FIG. 35, a shield member for shielding the noise of the electric and magnetic fields in the space  1   a,  or a sound absorbing member for preventing the resonance by absorbing the operating sounds, or a damper member having, e.g., viscous and elastic properties. This arrangement further improves the desired functions thereof. 
     3) Method of attaching the bezel 
     For the purpose of making the positional relationship accordant between the disk insertion port  104   a  of the front bezel  104  and the recording/reproducing device  1  when inserting device  1  therein, it is typically preferable to attache  attach the front bezel  104  to the recording/reproducing device  1 . In this embodiment, however, the key-like engaging members  102   b  are, as discussed above, shaped at upper ends of both side surfaces of the chassis  102  with a view to sustaining the front bezel  104  so as not to be inclined forward. The front bezel  104  is provided with the hook members  104   c  engaging with the engaging members  102   b.  After engaging the engaging members  102   b  with the hook members  104   c,  the front bezel  104  is fixed to the bottom surface of the chassis  102  with the screws  119 , thus providing a firm fixing structure. Based on this structure exhibiting a sufficient strength, even when grasping only the front bezel  104  during, e.g., a handling operation, no deformation is caused. 
     In this embodiment, the holding means for sustaining the front bezel  104  so as not to slant forward involves the use of the hook members  104   c  of the front bezel  104  which engage with the key-like engaging members  102   b  shaped at the upper ends of both side surfaces of the chassis  102 . The mode of engagement is not, however, confined to the above-mentioned. A possible engaging mode (not shown) is that, for instance, the front bezel  104  is engaged with the chassis  102  from inside. 
     The front bezel  104  is attached to the chassis  102  in the foregoing embodiment. The construction may, however, exclude the front bezel  104 . Instead, for example, an outer case of an electronic appliance like a computer may be formed with a disk insertion port. 
     4) Construction of relay board 
     The relay boards  105  and  105 A are singly provided in FIGS. 29 and 30. Whereas in FIGS. 31 and 32, there are provided the relay boards  115  and  115 A by twos. These arrangements do not present a functional difference therebetween. This simply implies that the one-sheet construction of the relay boards  105  and  105 A decreases the costs, while two-sheet construction of the relay boards  115  and  115 A exhibits a versatility of combination because of separability per unit by combining the boards with the recording/reproducing devices. 
     On the other hand, each of the relay boards  105 ,  105 A,  115  and  115 A includes the driving element  112  for increasing the current driving ability of-the  of the output signal of the 3.5-inch recording/reproducing device  1  up to a current value of the 5-inch FDD, . If the current of values on both sides are equal, there is no necessity for providing the driving element  112 . 
     5) Connection of relay board to recording/reproducing device 
     Referring to FIGS. 29 and 30, the electric power is supplied from the relay boards  105  and  115  via the power supply terminal  111  to the recording/reproducing device  1 . In FIGS. 30 and 32, the electric power is fed from the relay boards  105  and  115 A via the flat cable  110  to the recording/reproducing device  1 . These arrangements do not bring about any functional difference therebetween. This simply implies that the supply of electric power via the connectors  109  disposed at the end of the flat cable  110  leads to a drop in costs of construction, while the supply of electric power through the power supply terminal  111  has a good versatility of combination. It is because the latter arrangements accords with an electric power supplying method of the conventionally standardized 3.5-inch recording/reproducing device  1  which doe  dues not include special circuitry. 
     In the prior art example disclosed in Japanese Utility Model Laid-Open Publication No.63-11792, the relay boards are connected directly to the recording/reproducing devices through the connectors, which requires accurate positioning therebetween. In the foregoing embodiment, however, the connection is made through the flat cable  110 , and hence the necessity for the precise positioning process therebetween is eliminated. Besides, it is easy to change the combinations of the recording/reproducing devices  1  and the relay boards  105  and  115  or the recording/reproducing devices  1  and the relay boards  105 A and  115 A. The combinations can be diversified by anyone according to the purposes. 
     6) Placement of relay board of selective condition setting means: 
     Each of the relay boards  105 ,  105 A,  115  and  115 A which are shown in FIGS. 29 through 32 has a plurality of short plugs serving as selective condition setting means for selectively setting a driving state (typically referred to as a drive select) of the 3.5-inch recording/reproducing device i   1 or selectively the specifications thereof. Assuming that the above-mentioned selective condition setting means are incorporated into the 3.5-inch recording/reproducing devices shown in FIGS. 29 to  32 , the devices  1  are reduced in their thickness, and hence the selective positions have to be set in the confined space. This causes a deterioration in handling the condition setting process. Whereas in the illustrative embodiment of the present invention, the selective condition setting means are provided on the relay boards  105 ,  105 A,  115  and  115 A each having a sufficient space, thereby showing an extremely good state of handling the condition setting process. 
     One available arrangement, catered for a completely different application, of the short plugs  114  is that the plugs are used as test terminals for electrically monitoring, e.g., a driving state of the recording/reproducing device  1 . In connection with the test terminals for electrically monitoring the driving state thereof, there mat  may be provided, e.g., pattern lands on the relay boards  105 ,  105 A,  115  and  115 A having a large space as completely different electric monitoring means. 
     The foregoing illustrative embodiment has dealt with a plurality of short plugs  11   114 as selective condition setting means. Another available selective condition setting means may be switching means like, e.g., slide switches. 
     As discussed above, in the relay boards  105 ,  105 A,  115  and  115 A having the sufficient space, there are provided the controlling means for electrically controlling the recording/reproducing device  1  as in the case of selectively setting both the driving state of the recording/reproducing device  1  and the specifications thereof and further electrically monitoring the driving state. This arrangement yields a good handling property for setting the control conditions. 
     The characteristics of geometries in which the recording/reproducing devices  1  shown in FIGS. 29 through 36are provided have been described thus far. The explanation will next be focused on effects obtained when incorporating the thus constructed recording/reproducing devices into, e.g., a computer and utilizing the device therein by way of one example with reference to FIG. 37 illustrating the computer in perspective. 
     Turning to FIG. 37, the numeral  121  designates a computer device body, into which a variety of electronic units, for effecting electric processes;  122  a display for displaying on the basis of commands issued from the computer device body  121 ; and  123  a keyboard for inputting the commands to the device body  121 . 
     The computer device body  121  is mounted with two sets of 5-inch FDDs  124  as external storage units and one 5-inch HDD  125 . The computer device body  121  includes a preparatory mounting area  126 large enough to accommodate one additional external storage unit. The computer device body  121  receives software and data transferred from the 5-inch FDDs  124  or from the 5-inch HDD  125  or performs predetermined processes upon receiving the data. Excepting its functions and capability, a processing function and capability depend on a storage capacity and a data transferring velocity of the external storage unit. 
     Under such circumstances, there are made a good number of contrivances for the purpose of ameliorating the processing function and capability of the computer device body  121 . Much attention will be paid to an effective method which involves combinations of the external storage units incorporated into the computer device body  121 . 
     As previously stated, the external shape sizes, fitting dimensions and electrically connected interfaces of the FDDs, HDDs, ODDs and tape streamers, which have been standardized and thereby spread over as external storage units of multiple electronic appliances, are substantially standardized in conformity with sizes of respective recording mediums. On the other hand, the computers are in general constructed to exhibit a functional expandability. Take a device body of FIG. 37 for instance, the computer device body  121  is invested with minimum standard functions which characterize the system. For expanding the functions, there are prepared in advance connecting functions (not shown) to, e.g., additional slots of an electronic circuit board and to a variety of appliances to facilitate the functional expansions according to the purposes. Consequently, it is easy to combine or replace the external storage units mounted in the computer device body. The processing function and capability can be expanded according to the constitutional purposes of the system. Although the recording/reproducing devices shown in the prior art examples are appearing, the drawbacks to the installation thereof remain unsolved. Hence, the recording/reproducing devices in this embodiment care  are capable of increasing a degree of freedom for combinations of the external storage units and obviating such drawbacks inherent in the installation thereof. 
     Referring to FIG. 37, the combinations or replacement and installation of the external storage units incorporated in the computer device body  121  will concretely be described. 
     The computer device body  121  depicted in FIG. 37 has a quite typical construction and is mounted with two 3.5-inch FDDs  124  which are commonly used for loading or copying commercially available software and backing up the data. The 5-inch HDDs  125 , which store a good deal of software and data, perform a function to effect a high-speed transfer to the computer device body  121 . 
     On the occasion of a usable functional expansion of the software recorded on the 3.5-inch recording medium, the 5-inch FDDs  124  are removed, and instead there is taken a method of mounting the recording/reproducing devices each having a recording/reproducing mechanism. In the prior art recording/reproducing devices, however, if the 5-inch FDDs  124  are taken away, the 5-inch recording/reproducing function can not be accomplished. 
     To cope with this, in accordance with the embodiment of the present invention there are employed two sets of 3.5-inch recording/reproducing devices, and the following arrangement will be adopted. 
     (1) One of the two 5-inch FDDs  124  is removed, and, as described above, even when the FDD  124  is replaced with the two miniaturized 3.5-inch recording/reproducing devices  1 , the 5-inch recording/reproducing function can be fulfilled because of the single 5-inch FDD  124  being left. Moreover, the preparatory mounting area  126  remains as it is for mounting the additional external storage unit. 
     Note that the function of the single FDD may generally suffice in the computer device body loaded with the HDDs. 
     (2) If the device body is loaded with no 5-inch HDD  125  (in some cases the preparatory mounting area  126  is not provided), and when mounting two sets of 3.5-inch recording/reproducing devices in this embodiment, there will be produced no obstacle to the 5-inch recording/reproducing functions, because the two 5-inch FDDs  124  are left as they are. 
     (3) Supposing that no preparatory mounting area  126  is formed in the device body mounted with only two 5-inch FDDs  12 , and when one of the 5-inch FDDs  124  taken away is replaced with the two 3.5-inch recording/reproducing devices of this embodiment, a single set of 5-inch FDD  124  is left; or alternatively this-permits incorporation of other external storage unit. 
     (4) If no mounting area  126  is provided in the computer device body mounted with only one 5-inch FDD  124 , one of the 5-inch FDDs  124  taken away is replaced with two sets of 3.5-inch recording/reproducing devices of this embodiment. In this case, the function of the computer device body incorporating the two 3.5-inch recording/reproducing devices can be expanded with almost no modification added to the computer device body. 
     ( 54 )  ( 5 ) As a matter of course, the two 5-inch FDDs  124  and one 5-inch HDD  125  stand as they are. Where the two 3.5-inch recording/reproducing devices are mounted in the preparatory mounting area  126 , there will be caused no obstacle to the conventional recording/reproducing function. 
     By utilizing the arrangement given above, the two 3.5-inch recording/reproducing devices can be incorporated into the space the size of which is substantially equal to the conventional standardized 5-inch FDD  124 . Hence, the usable functional expansion of the software recorded on the 3.5-inch recording mediums can be effected. In that case, the function can be expanded with facility without causing obstacles to the conventional recording/reproducing function as well as by effecting no improvement or modification with respect to the hardware of the computer device body  121 . 
     The foregoing embodiment has exemplified a case where the functional expansion is executed in the conventional system. As a matter of course, in a novel system, however, it is much easier to exhibit many characteristics discussed above. In this embodiment, the explanation has been made by exemplifying the 5-inch and 3.5-inch FDDs. It is, of course, obvious that the arrangement is not limited to the combinations of these FDDs. The combination may be diversified like this;, for instance, 5-inch FDDs and 3.5-inch FDDs, or 8-inch FDDs and 5-inch FDDs. These changes in combination mode can be applied to HDDs and ODDS. 
     INDUSTRIAL APPLICABILITY 
     As discussed above, the recording/reproducing devices in accordance with the present invention can remarkably be miniaturized and particularly reduced in the device thickness. When employing the devices as external storage units for electronic appliances such as computers, the space for placement can be diminished to the greatest possible degree, thereby miniaturizing the electronic appliance as a whole. It is also possible to increase degrees of freedom both of placement of the recoding  recording/reproducing devices-and of design. In particular, since the thickness of the recording/reproducing device is,  set to 20.5 mm or under, for example, the two 3.5-inch recording/reproducing devices according to the present invention can be incorporated in place of the 5-inch recording/reproducing devices which have hitherto been constituted to have a thickness of typically 41 mm. General purposes of this type of recording/reproducing device can be considerably enlarged. Therefore, as mentioned earlier, the recording/reproducing device is effective in the case of making usable a different standard, e.g., 3.5-inch recoding medium in the electronic appliance which employs the 5-inch recording medium or in the case of making usable both of the recoding  recording mediums of different standards. Especially, the 3.5-inch recording medium presents a high reliability in handling as compared with the 5-inch recording medium. For this reason, a capacity of the 3.5-inch recording/reproducing device is lately increased with acceleration. Under such circumstance, the present invention is suitable for a development of the software technology, and software unattainable by the software recorded on the convectional  conventional 3.5-inch recording medium can be actualized. 
     The essentiality in the software technology, even though overwhelmingly advanced new techniques are introduced, lies in interchangeability with the software which has hitherto been accumulated or in continuous operability of the conventional software. The present invention is concerned with this point and therefore deal  deals with free systematization of the FDDs, HDDs, ODDs and tape streamers which have been standardized and the  spread over as external storage units of a variety of electronic appliances in association with the software techniques. Consequently, it is feasible to obtain the interchangeability with the conventionally accumulated software or the operability of the conventional software and further to develop the software technology business aiming at facilitating an expansion of total system. With a view to expanding the functions of convectional  conventional system, it is possible to develop new and easy-to-diversify businesses which can not be seen in the past but facilitate the expansion of total system by simple and inexpensive means without requiring both tremendous investments of assets and high special hardware techniques, these businesses including, for instance, a unit sale business associated with the recoding  recording/reproducing devices shown in the foregoing embodiment, a set sale business of the recording/reproducing devices and related software techniques, a set sale business of the recording/reproducing devices and other external storage units or a set sale business of the recording/reproducing devices and the function expanding circuit boards. 
     Although the illustrative embodiment of the present invention has been described in detail with reference to the accompanying drawings, it is to be understood that the present invention is not limited to that precise embodiment. Various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.