Patent Publication Number: US-6985329-B2

Title: Magnetic disk cartridge

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a magnetic disk cartridge, and more particularly to a small magnetic disk cartridge that is inserted and loaded in a disk drive provided in small electronic equipment such as a digital camera, a laptop computer, etc. 
     2. Description of the Related Art 
     To record or reproduce information, a recording medium is removably inserted in the card slot of electronic equipment such as a digital still camera, a digital video camera, a laptop computer, etc. Such recording media in practical use are of a semiconductor memory type, a hard disk type, an optical disk type, a magnetic disk type (e.g., a floppy disk type), etc. 
     Among these recording media, semiconductor memories are most widely used because they are easy to handle and have a relatively large recording capacity. However, they are relatively expensive. Because of this, in digital cameras employing the semiconductor memory, the photographed image data is transferred to a PC and stored, the data is deleted from the memory, and the semiconductor memory is repeatedly used. 
     Hard disks are similarly expensive, although some of them can store 340 megabytes (MB) of data or 1 gigabytes (GB) of data. Because of this, data is transferred to another device and stored, and hard disks are repeatedly used. 
     Optical disks have a large recording capacity for their size. For example, an optical disk with a size of 35 mm×41 mm×11 mm can store 260 MB of data. Optical disks with a recording capacity of 512 MB are about to be realized. However, optical disks have the disadvantage that the recording speed is slow, because their writing time is time-consuming. 
     Some magnetic disks such as a floppy disk have a small size of 50 mm×55 mm×2 mm. Such a small magnetic disk can be exchangeably loaded in a disk drive of a size that can be inserted into the card slot of a PC, etc. However, the recording capacity is as small as 40 MB and insufficient to record image data photographed by a camera. In addition, the size is not suitable for digital cameras. 
     With the spread of PCs, digital cameras have spread rapidly in recent years because of the simplicity of recording, enhancement in picture quality due to the development of imaging elements, possibility of data deletion and transmission, recording capacity size, etc. However, the method of use is restricted, because recording media are limited in cost and recording capacity, as described above. For instance, since recording media are very expensive, a single camera has only a single recording medium, which is repeatedly used. That is, when the recording medium is filled with data, the data is transferred to a PC and deleted. Because of this, there are cases where the recording medium is filled up during a trip. In such a case, the recording medium cannot be stored along with data and cannot be given away to a person. 
     The realization of a recording medium which is large in recording capacity, low in cost, and small in size so that the data photographed by a digital camera can be stored or given away to a person is desired. With regard to PCs as well, the realization of a recording medium which is large in recording capacity, low in cost, and small in size so that data can be stored thereon and handed to a person is desired. 
     To meet the aforementioned demands, it is contemplated that the above-described inexpensive small large-capacity recording medium may comprise a card-type disk drive which is loaded in electronic equipment such as a PC and a digital camera, and a magnetic disk cartridge which is loaded in the card-type disk drive. That is, it is contemplated that such a magnetic disk cartridge may include a housing in which a flexible magnetic disk is rotatably housed, and have a recording capacity of 200 MB or larger. Examples of high density magnetic recording media are a recording medium with a thin metal film formed by vapor deposition, a recording medium with a thin metal film formed by sputtering, and a recording medium employing barium ferrite powder or ferromagnetic magnetic powder. An example of a high density magnetic recording medium employing barium ferrite powder is disclosed in Japanese Patent Application No. 2001-312864. 
     The “high density magnetic recording medium employing barium ferrite powder” is a magnetic disk containing barium ferrite powder in a magnetic layer, and employs a material capable of high-recording density. The magnetic disk may comprise a magnetic recording medium disclosed in, for example, Japanese Patent Application No. 2001-205290. The magnetic recording medium has a non-magnetic layer which includes both non-magnetic powder and a binder, and a magnetic layer which includes both ferromagnetic powder (which is ferromagnetic metal powder or hexagonal-system ferrite powder) and a binder on at least one surface of a nonmagnetic substrate. The non-magnetic layer and the magnetic layer are formed on at least one side of a non-magnetic supporting body in the recited order. In the non-magnetic layer, the quantity of carbon black whose average particle diameter is 10 to 30 nm is 10 to 50 weight parts with respect to 100 weight parts of the aforementioned non-magnetic powder. The thickness of the magnetic layer is 0.2 μm or less. According to a microanalysis by an electron beam, the standard deviation (b) of the strength of an element with respect to an average strength (a) resulting from ferromagnetic powder is 0.03≦b/a≦0.4. The center plane average roughness Ra of the magnetic layer is 5 nm or less, and the 10-point average roughness Rz is 40 nm or less. In a magnetic disk employing the above-described material, information is recorded or reproduced by a magnetic head such as an MR head capable of high-recording density. 
     The above-described magnetic recording medium can have a recording capacity of 200 MB or larger, preferably 500 MB or larger. Therefore, if a still image has 1 MB of data per sheet, the magnetic recording medium can store 500 sheets. In the case of a dynamic image, the magnetic recording medium can store image contents of about 30 minutes. Thus, the magnetic recording medium can store a dynamic image photographed by a digital camera, and a dynamic image transmitted by a portable telephone. As a result, users can conveniently use the magnetic recording medium. Furthermore, the magnetic recording medium can be conveniently used in PCs as an inexpensive large-capacity recording medium. Thus, the convenience is great. 
     Preferred examples of disk drives in the present specification include disk drives incorporated in PCs, digital cameras, etc., as well as other types of disk drives. In the case of PCs, there are a disk drive  1 ′ shown in  FIG. 32A , and disk drives incorporated in a PC card, such as “click!” (registered trademark). The disk drive  1 ′ is connected electrically with a socket  7  of the receiving portion of a card  6  that is inserted in a PC card slot provided in a PC. In the case of a digital camera  8 , as shown in  FIG. 32B , there is a small disk drive  1 ′ that is connected electrically with the socket of the receiving portion  9  of the camera  8 . Therefore, the small disk drive  1 ′ is extremely small in size and has, for example, a length of 38 to 55 mm, a width of 35 to 51 mm, and a thickness of 3 to 5 mm. A magnetic disk cartridge  10 ′ has, for example, a length and a width of 25 to 36 mm and a thickness of 1 to 3 mm. 
     Incidentally, it has been proposed that the housing of such a subminiature magnetic disk cartridge is formed into the shape of a disk so that the magnetic recording medium can be handled like a coin. That is, if the magnetic recording medium can be handled with the same ease that a coin is inserted into the slot of a vending machine, the convenience can be enhanced. 
     In such a type of magnetic recording medium, the magnetic disk is provided in a housing and protected, as with conventional floppy disks. When the magnetic recording medium is loaded in a small disk drive, and information is recorded or reproduced, a shutter provided in the housing is moved so that the magnetic disk is exposed, thereby providing access thereto. 
     Even in the case of the housing formed into the shape of a disk, it is necessary to insert the housing in a predetermined direction so that information can be recorded or reproduced. If the housing is formed into the shape of a disk, however, the housing can be inserted into a disk drive regardless of the position of the shutter, because it has no directionality. That is, there is a possibility that the magnetic disk cartridge will be inserted into a disk drive in a direction where information recording and reproduction cannot be performed. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above-described circumstances. Accordingly, it is the primary object of the present invention to provide a magnetic disk cartridge that can be loaded in a disk drive in a direction where information recording and reproduction can be performed, even when the housing is formed into the shape of a disk. 
     To achieve this end and in accordance with the present invention, there is provided a first magnetic disk cartridge for use in a disk drive having both a slot and a guide portion. The magnetic disk cartridge comprises a generally disk-shaped housing in which a magnetic disk is rotatably housed, and protrusions. The protrusions are formed on a main surface of the housing and are used for positioning the magnetic disk cartridge in a direction capable of recording and reproduction in cooperation with the guide portion of the disk drive when the magnetic disk cartridge is loaded in the disk drive. 
     In the first magnetic disk cartridge of the present invention, it is preferable that the aforementioned housing comprise at least one opening into which a magnetic head of the disk drive is inserted, and at least one shutter for opening or closing the opening. 
     It is preferable that the aforementioned protrusions comprise at least two protrusions disposed along a straight line passing through the center of the main surface of the housing, and across the center. 
     It is further preferable that the aforementioned protrusions also comprise first and second protrusions disposed along a straight line passing through the center of the main surface of the housing, and across the center. The distance of the first protrusion from the center may be different from that of the second protrusion. 
     In the magnetic disk cartridge of the present invention, the height of the first protrusion from the main surface of the housing maybe substantially equal to that of the second protrusion The height of the first protrusion from the main surface of the housing may also be different from that of the second protrusion. 
     In the magnetic disk cartridge of the present invention, in the case that the heights of the protrusions differ, it is preferable that the first protrusion is disposed at a position close to the center. The second protrusion may be disposed at a position farther away from the center. It is preferable that the height of the first protrusion may be lower than that of the second protrusion. 
     The aforementioned housing may be equipped with a plurality of openings each having a shutter. In this case, the protrusions are used to locate any one of a plurality of openings at a position capable of recording and reproduction in cooperation with the guide portion of the disk drive when the magnetic disk cartridge is loaded in the disk drive. 
     In the magnetic disk cartridge of the present invention, the aforementioned housing may have on its side face a pair of openings that have the shutter and are symmetrical with respect to the center of the main surface of the housing. The housing may also have cutouts that communicate with the openings and are formed in the main surface. The protrusions may be provided to cover the cutouts. 
     The “main surface of the housing” refers to one of the top and bottom surfaces of a generally disk-shaped housing. It is necessary that the aforementioned protrusion protrude from the main surface. The protrusion has a height such that it is guided to the guide portion of the disk drive or abuts the guide portion. The protrusions may be formed integrally with the housing. Alternatively, they may be separate members. The separate protrusions may be fixed on the main surface by an adhesive, etc. The protrusions may be normally housed in the housing, if they protrude when the magnetic disk cartridge is loaded in a disk drive. 
     Further in accordance with the present invention, there is provided a second magnetic disk cartridge for use in a disk drive having both a slot and a protruding portion. The second magnetic disk cartridge comprises a generally disk-shaped housing in which a magnetic disk is rotatably housed, and a guide groove for positioning the magnetic disk cartridge in a direction capable of recording and reproduction in cooperation with the protruding portion provided within the slot of the disk drive when the magnetic disk cartridge is loaded in the disk drive. 
     In the second magnetic disk cartridge of the present invention, it is preferable that the guide groove is formed in a main surface of the housing along a straight line passing through the center of the main surface. It is also preferable that the guide groove has a broad portion which widens toward the outer circumference of the main surface. 
     In the first and second magnetic disk cartridges of the present invention, the magnetic disk may comprise a high density magnetic recording medium employing barium ferrite powder. 
     In accordance with the first magnetic disk cartridge, protrusions are provided on the main housing of the housing to position the magnetic disk cartridge in a direction capable of recording and reproduction in cooperation with the guide portion of the disk drive when the magnetic disk cartridge is loaded in the disk drive. Therefore, even if the housing is formed into the shape of a disk, the magnetic disk cartridge can be positioned within the disk drive in a direction of capable of recording and reproduction. 
     In the case where two protrusions are disposed along a straight line passing through the center of the main surface of the housing and are disposed across the center, the magnetic disk cartridge can be reliably located at a position where the magnetic head of the disk drive can access a magnetic disk, in cooperation with the guide portion of the disk drive, even when the magnetic disk cartridge is inserted into the disk drive at any angle. After the magnetic disk cartridge is loaded in the disk drive, positional shift of the magnetic disk cartridge can be prevented. 
     Particularly in the case where the two protrusions have different heights from the main surface, a guide groove is provided in the disk drive so that the protrusion lower in height can move into the groove and the protrusion higher in height cannot move into the groove. Therefore, there is an advantage that positioning of the magnetic disk cartridge becomes extremely easy. 
     In the case where the housing is equipped with a plurality of openings having a shutter, any one of the openings can be positioned in a direction capable of recording and reproduction by the above-described protrusions. Therefore, even if the housing is formed into the shape of a disk, the magnetic disk cartridge can be reliably located within the disk drive at a direction of capable of recording and reproduction. 
     As described above, the aforementioned housing may have on its side face a pair of openings that have the shutter and are symmetrical with respect to the center of the main surface of the housing. This housing also has cutouts that communicate with the openings and are formed in the main surface. The protrusions are provided to cover the cutouts. In this case, at the position of the cutout, the height of the opening in the thickness direction can be increased by the quantity of the cutout. Therefore, it becomes possible to insert a plurality of magnetic heads into the opening. As a result, a magnetic disk cartridge with a large recording capacity can be provided. 
     In accordance with the second magnetic disk cartridge of the present invention, the housing has a guide groove for positioning the magnetic disk cartridge in a direction capable of recording and reproduction in cooperation with the protruding portion provided within the slot of the disk drive when the magnetic disk cartridge is loaded in the disk drive. Therefore, the magnetic disk cartridge can be inserted smoothly into the slot of the disk drive. Furthermore, the magnetic disk cartridge is guided into the disk drive by cooperation of the guide groove of the magnetic disk cartridge and the protruding portion of the disk drive. Therefore, smooth insertion and reliable positioning of the magnetic disk cartridge becomes possible and incorrect insertion can be prevented. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be described in further detail with reference to the accompanying drawings wherein: 
         FIG. 1  is a perspective view showing how a magnetic disk cartridge according to the present invention is used in a digital camera; 
         FIG. 2  is a perspective view showing how the magnetic disk cartridge according to the present invention is used in a PC card for a PC; 
         FIG. 3A  is a perspective view showing a magnetic disk cartridge constructed in accordance with a first embodiment of the present invention, and a disk drive in which the magnetic disk cartridge is loaded; 
         FIG. 3B  is a plan view of the magnetic disk cartridge loaded in the disk drive, the upper plate of a housing  2  being removed to show a guide portion; 
         FIG. 4A  is a plan view showing the detailed structure of the magnetic disk cartridge shown in  FIG. 3A ; 
         FIG. 4B  is a bottom view showing the detailed structure of the magnetic disk cartridge shown in  FIG. 3A ; 
         FIG. 4C  is a sectional view showing the detailed structure of the magnetic disk cartridge shown in  FIG. 3A ; 
         FIGS. 5A to 5C  are plan views of how the magnetic disk cartridge of  FIG. 4  is inserted into the disk drive; 
         FIGS. 6A to 6C  are plan views showing modifications of the disk drive; 
         FIG. 7  is a perspective view showing a magnetic disk cartridge constructed in accordance with a second embodiment of the present invention; 
         FIG. 8A  is a plan view of the magnetic disk cartridge shown in  FIG. 7 ; 
         FIG. 8B  is a bottom view of the magnetic disk cartridge shown in  FIG. 7 ; 
         FIG. 8C  is a sectional view of the magnetic disk cartridge shown in  FIG. 7 ; 
         FIG. 9A  is a perspective view showing the magnetic disk cartridge of  FIG. 8 , and a disk drive in which the magnetic disk cartridge is loaded; 
         FIG. 9B  is a plan view of the magnetic disk cartridge loaded in the disk drive, the upper plate of a housing being removed to show a guide portion; 
         FIGS. 10A to 10C  are plan views of how the magnetic disk cartridge of  FIG. 8  is inserted into the disk drive; 
         FIG. 11A  is a plan view showing a magnetic disk cartridge and a disk drive constructed in accordance with a third embodiment of the present invention; 
         FIG. 11B  is a plan view showing a magnetic disk cartridge and a disk drive constructed in accordance with a fourth embodiment of the present invention; 
         FIG. 12A  is a perspective view showing a magnetic disk cartridge constructed in accordance with a fifth embodiment of the present invention; 
         FIG. 12B  is a plan view of the magnetic disk cartridge shown in  FIG. 12A ; 
         FIG. 13A  is a sectional view of the magnetic disk cartridge shown in  FIG. 12 ; 
         FIG. 13B  is a bottom view of the magnetic disk cartridge shown in  FIG. 12 ; 
         FIG. 14A  is an enlarged perspective view showing the opening of the magnetic disk cartridge shown in  FIGS. 12 and 13 ; 
         FIG. 14B  is an enlarged sectional view showing the opening of the magnetic disk cartridge shown in  FIGS. 12 and 13 ; 
         FIG. 15A  is a perspective view showing the magnetic disk cartridge of  FIGS. 12 and 13 , and a disk drive in which the magnetic disk cartridge is loaded; 
         FIG. 15B  is a plan view of the magnetic disk cartridge loaded in the disk drive, the upper plate of a housing being removed to show a guide portion; 
         FIG. 16A  is a perspective view showing a magnetic disk cartridge constructed in accordance with a sixth embodiment of the present invention; 
         FIG. 16B  is an enlarged perspective view of the slot of a disk drive in which the magnetic disk cartridge of  FIG. 16A  is loaded; 
         FIG. 17  is a plan view showing the state in which the magnetic disk cartridge of  FIG. 16  is loaded in the disk drive; 
         FIG. 18A  is a plan view showing a magnetic disk cartridge constructed in accordance with a seventh embodiment of the present invention; 
         FIG. 18B  is a side view of the magnetic disk cartridge shown in  FIG. 18A ; 
         FIG. 18C  is a plan view of a disk drive into which the magnetic disk cartridge of  FIG. 18A  is inserted; 
         FIG. 19A  is a plan view showing the state in which the magnetic disk cartridge of  FIG. 18  is loaded in the disk drive; 
         FIG. 19B  is a bottom view showing the state in which the magnetic disk cartridge of  FIG. 18  is loaded in the disk drive; 
         FIG. 19C  is a side view showing the state in which the magnetic disk cartridge of  FIG. 18  is loaded in the disk drive; 
         FIG. 20A  is a plan view showing a magnetic disk cartridge constructed in accordance with an eighth embodiment of the present invention; 
         FIG. 20B  is a side view of the magnetic disk cartridge shown in  FIG. 20A ; 
         FIG. 20C  is a sectional view of the magnetic disk cartridge shown in  FIG. 20A ; 
         FIG. 21  is a plan view showing a first modification of the magnetic disk cartridge shown in  FIG. 20 ; 
         FIG. 22A  is a perspective view showing a second modification of the magnetic disk cartridge shown in  FIG. 20 ; 
         FIG. 22B  is a plan view of  FIG. 22A ; 
         FIG. 22C  is a side view of  FIG. 22B ; 
         FIG. 23A  is a plan view showing the state in which the magnetic disk cartridges of  FIG. 22  are housed within a case; 
         FIG. 23B  is a side view showing the state in which the magnetic disk cartridges of  FIG. 22  are housed within the case; 
         FIG. 23C  is a sectional view showing the state in which the magnetic disk cartridges of  FIG. 22  are housed within the case; 
         FIG. 24A  is a plan view showing a magnetic disk cartridge constructed in accordance with a ninth embodiment of the present invention; 
         FIG. 24B  is a bottom view of the magnetic disk cartridge shown in  FIG. 24A ; 
         FIG. 24C  is a side view of the magnetic disk cartridge shown in  FIG. 24A ; 
         FIG. 25A  is a plan view showing a magnetic disk cartridge constructed in accordance with a tenth embodiment of the present invention; 
         FIG. 25B  is a bottom view of the magnetic disk cartridge shown in  FIG. 25A ; 
         FIG. 26A  is a plan view showing a magnetic disk cartridge constructed in accordance with an eleventh embodiment of the present invention; 
         FIG. 26B  is a plan view showing a modification of the magnetic disk cartridge of  FIG. 26A ; 
         FIG. 26C  is a plan view showing a disk drive in which the magnetic disk cartridge of  FIG. 26A  or  26 B is loaded; 
         FIGS. 27A and 27B  are plan views showing the state in which the magnetic disk cartridge of  FIG. 26A  is loaded in the disk drive of  FIG. 26C ; 
         FIGS. 27C and 27D  are plan views showing the state in which the magnetic disk cartridge of  FIG. 26B  is loaded in the disk drive of  FIG. 26C ; 
         FIGS. 28A to 28D  are plan views of disk drives with different shapes; 
         FIGS. 29A to 29C  are diagrams showing a list of shapes of magnetic cartridges and disk drives; 
         FIGS. 30A to 30D  are diagrams showing a list of shapes of magnetic cartridges and disk drives; 
         FIGS. 31A to 31I  are plan views showing various shapes of magnetic disk cartridge housings; 
         FIG. 32A  is a perspective view showing a magnetic disk cartridge on which the present invention is based, and a disk drive for a PC in which the disk cartridge is loaded; and 
         FIG. 32B  is a perspective view showing the magnetic disk cartridge on which the present invention is based, and a disk drive for a digital camera in which the disk cartridge is loaded. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will hereinafter be described in detail with reference to the drawings. Note that to facilitate comprehension, the components depicted in the figures are shown with their dimensions at different ratios from those in actuality. 
       FIG. 1  is a perspective view that shows how a magnetic disk cartridge according to the present invention is used in a digital camera. The magnetic disk cartridge  10  with a rotatable magnetic disk housed therein is loaded in a disk drive  1  through a slot-shaped opening  3  formed in the housing  2  of the disk drive  1 . The disk drive  1  is equipped with a drive mechanism for rotating a magnetic disk, a magnetic head for recording or reproducing information on or from the magnetic disk, and an input-output interface for communicating with electronic equipment such as a digital camera, a PC, to which the disk drive  1  is mounted. 
     When information is recorded on or reproduced from the magnetic disk, the magnetic disk cartridge  10  is first loaded in the disk drive  1 . Then, the disk drive  1  with the magnetic disk cartridge  10  is inserted, for example, into a slot provided in electronic equipment such as a digital camera, etc. Next, information is recorded on or reproduced from the magnetic disk of the magnetic disk cartridge  10  through the disk drive  1  by electronic equipment such as a digital camera, etc. 
       FIG. 2  shows a magnetic disk cartridge  10 , which is inserted into the slot-shaped opening  3  of a disk drive  1 . The disk drive  1  is connected electrically with the socket  7  of the receiving portion of a PC card  6 , which is inserted into a PC card slot provided in a PC. 
     In the magnetic disk cartridge  10  shown in  FIG. 1  or  2 , a magnetic disk is rotatably housed within a disk housing, shaped like a coin. The magnetic disk is preferably a high density magnetic recording medium employing barium ferrite powder. 
       FIG. 3  shows a magnetic disk cartridge  10  constructed in accordance with a first embodiment of the present invention, and a disk drive  1  in which the magnetic disk cartridge  10  is loaded.  FIG. 3A  shows a perspective view of the unloaded state.  FIG. 3B  shows a plan view of the loaded state, the upper plate  2 B of a housing  2  being removed to show a guide portion. 
     The housing  2  of the disk drive  1  has a flat space for housing the magnetic disk cartridge  10 , between a lower plate  2 A and an upper plate  2 B. Although not shown, the housing  2  also has a drive mechanism for rotating a magnetic disk, a magnetic head, a magnetic-head holder for supporting the magnetic head, and a signal processing section for recording or reproducing information between the magnetic head and the magnetic disk. 
     The housing  2  of the disk drive  1  is further provided with an opening  3 , a guide portion  4 , and an input-output interface  5 . The opening  3  is formed in one side face of the housing  2 , and through this opening  3 , the magnetic disk cartridge  10  is inserted into the housing  2 . 
     The guide portion  4  is formed in the upper plate  2  (thickness W 1 ) of the housing  2  and extends from the opening  3  toward the input-output interface  5 . The guide portion  4  is constructed by a first guide portion  4   a  and a second guide portion  4   b . The first guide portion  4   a  consists of curved surfaces extending from both sides  3   a  and  3   b  of the opening  3  toward the centerline  3   b  of the housing  2 . The second guide portion  4   b  consists of a groove (depth W 2 ) formed in the bottom surface of the upper plate  2 B of the housing  2  along the centerline  3   b  of the housing  2 . The first guide portion  4   a  has the function of contacting the protrusion  13   a  or  13   b  of the magnetic disk cartridge  10  and guiding the protrusion  13   a  or  13   b  toward the centerline  3   b , when the magnetic disk cartridge  10  is inserted into the disk drive  1  through the opening  3 . 
     Meanwhile, the magnetic disk cartridge  10  is equipped with a housing  11 , which has an outer diameter and a thickness slightly smaller than the width and height of the opening  3  of the disk drive  1 . This housing  11  has the above-described protrusions  13   a  and  13   b  on the main surface  11   a . The radially inner and outer protrusions  13   a  and  13   b  are provided along the centerline CL passing through the center point CP of the main surface  11   a  and across the center point CP. 
     The radially inner protrusion  13   a  is provided at a position close to the center point CP of the main surface  11   a , while the radially outer protrusion  13   b  is provided near the outer edge of the main surface  11   a . In addition, the radially inner protrusion  13   a  is lower in height than the radially outer protrusion  13   b  and has a height capable of being inserted into the second guide portion  4   b  of the disk drive  1 . The radially outer protrusion  13   b  has a height capable of preventing it from being inserted into the second guide portion  4   b.    
     Therefore, when the magnetic disk cartridge  10  is loaded in the disk drive  1 , the radially inner protrusion  13   a  can move within the second guide portion  4   b  along the centerline  3   b . If the radially inner protrusion  13   a  reaches the end of the second guide portion  4   b , the movement of the magnetic disk cartridge  10  in the direction of arrow A is stopped. On the other hand, the radially outer protrusion  13   b  is vertically aligned in the vicinity of the inlet of the second guide portion  4   b  with the centerline  3   b , as shown in  FIG. 3B . In this way, the magnetic disk cartridge  10  is disposed at a position where information can be recorded on or reproduced from the magnetic disk. 
     On the other hand, in the case where the radially outer protrusion  13   b  is first inserted when the magnetic disk cartridge  10  is loaded in the disk drive  1 , the radially outer protrusion  13   b  cannot move into the second guide portion  4   b  because of its height and therefore the magnetic disk cartridge  10  cannot be loaded in the disk drive  1 . In addition, the magnetic disk cartridge  10  cannot be inserted into the disk drive  1  if it is flipped because of the protrusions  13   a  and  13   b . Furthermore, the presence of the protrusions  13   a  and  13   b  makes it possible to discriminate the top surface of the magnetic disk cartridge  10  from the bottom surface by the sense of touch. 
     Note that even in the case where the height of the radially outer protrusion  13   b  is made the same as that of the radially inner protrusion  13   a  so that the radially outer protrusion can also move into the second guide portion  4   b , the magnetic disk cartridge  10  facing in the opposite direction cannot be loaded in the disk drive  1 , if the distance of the radially inner protrusion  13   a  from the center point CP differs from that of the radially outer protrusion  13   b . That is, because the radially outer protrusion  13   b  is formed near the outer edge of the main surface  11   a , the magnetic disk cartridge  10  cannot be completely inserted into the disk drive  1 , even if the radially outer protrusion  13   b  moves into the second guide portion  4   b  and reaches the end of the second guide portion  4   b.    
     The input-output interface  5  is disposed, for example, on the front face of the housing  2  at the opposite end from the opening  3 . This input-output interface  5  is connected electrically with electronic equipment such as a PC, a digital camera, a personal digital assistant (PDA), a portable telephone, etc. Information to be recorded on the magnetic disk within the magnetic disk cartridge  10  is input via the input-output interface  5 , while information reproduced from the magnetic disk is output from the input-output interface  5 . 
       FIG. 4  shows the detailed structure of the magnetic disk cartridge  10  shown in  FIG. 3 , wherein  FIG. 4A  is a plan view,  FIG. 4B  is a bottom view, and  FIG. 4  is a schematic cross sectional view taken along the center line CL. 
     The magnetic disk cartridge  10  is equipped with a generally disk-shaped housing  11  of resin. Within the housing  11 , a magnetic disk D is rotatably housed. The housing  11  is provided with a shutter  12  and protrusions  13   a  and  13   b . The housing  11  further has a flat space  14  for housing the magnetic disk D. The magnetic disk D is held within the housing  11  by a center core  15 . The center core  15  is exposed through a hole formed in the bottom surface  11   b  of the housing  11 . If the center core  15  is connected with the spindle of the disk drive  1 , the magnetic disk D held by the center core  15  is rotated. 
     The shutter  12 , movably attached to the housing  11 , is opened when the magnetic disk cartridge  10  is loaded in the disk drive  11 , and it is closed when the magnetic disk cartridge  10  is ejected from the disk drive  11 . If the shutter  12  is opened, a portion of the magnetic disk D is exposed and information can be recorded or reproduced. 
     The main surface  11   a  of the housing  11  is provided with two protrusions  13   a  and  13   b . These protrusions  13   a  and  13   b  may be formed integrally with the housing  11 . Alternatively, they may be formed separately from the housing  11  and fixed on the main surface  11   a  by an adhesive, etc. 
     As described above, the protrusions  13   a  and  13   b  are provided on the centerline CL passing through the center point CP of the main surface  11   a  of the housing  11  and across the center point CP. The heights H 1  and H 2  of the protrusions  13   a  and  13   b  may be the same or different, as long as they protrude from the main surface  11   a . For example, if the height H 1  of the protrusion  13   a  close to the shutter  12  is lower than the height H 2  of the other protrusion  13   b , only the radially inner protrusion  13   a  can be inserted into the second guide portion  4   b . Therefore, this case is preferable. 
     That is, only when the radially inner protrusion  13   a  is inserted into the second guide portion  4   b  can the magnetic disk cartridge  10  be loaded in the disk drive  1 . On the other hand, the radially outer protrusion  13   b  cannot be inserted into the second guide portion  4   b  because of the height H 2 , so the magnetic disk cartridge  10  cannot be loaded in the disk drive  1 . In such a case, if a user rotates the magnetic disk cartridge  10  in the direction of arrow R 1 , the radially inner protrusion  13   a  will be positioned in a direction capable of contacting the second guide portion  4   b.    
     In this way, the magnetic disk cartridge  10  can be reliably loaded in the disk drive  1  in a direction capable of recording or reproducing information. As a result, users can be prevented from mistaking the inserting direction of the magnetic disk cartridge  10 . In addition, if the heights of the protrusions  13   a  and  13   b  are made different from each other, users can recognize the inserting direction of the magnetic disk cartridge  10  with the sense of touch. Therefore, even if the magnetic disk cartridge  10  is formed into the shape of a disk, mistaking the inserting direction can be prevented. 
     Note that in the case where the two protrusions  13   a  and  13   b  are the same in height, a recess may be provided around the radially outer protrusion  13   b  so that users can recognize the inserting direction of the magnetic disk cartridge  10  with the sense of touch and can easily grip the magnetic disk cartridge  10 . 
     The radially inner protrusion  13   a  is disposed at a position away from the center point CP of the main surface  11   a  by distance d 1 . The radially outer protrusion  13   b  is disposed at a position away from the center point CP by distance d 2 , which is greater than distance d 1  (d 2 &gt;d 1 ). Therefore, when the magnetic disk cartridge  10  is inserted into the disk drive  1  with the radially inner protrusion  13   a  facing toward the first guide portion  4   a , the protrusion  13   a  first contacts the first guide portion  4   a . As a result, the magnetic disk cartridge  10  is rotated and moved along the first guide portion  4   a , or it is rotated and moved because the side face of the housing  11  abuts the opening  3 . Therefore, if the user inserts the magnetic disk cartridge  10  while rotating it along the direction of rotation, the magnetic disk cartridge  10  is positioned so that the radially inner protrusion  13   a  is inserted into the second guide portion  4   b.    
     On the other hand, when the radially outer protrusion  13   b  is first contacted with the first guide portion  4   a , the radially inner protrusion  13   a  does not contact the first guide portion  4   a , because the distance d 1  is shorter than the distance d 2 . Therefore, the magnetic disk cartridge  10  rotates toward a direction where there is no mechanical contact resistance, and the radially inner protrusion  13   a  is brought into contact with the first guide portion  4   a . If the user inserts the magnetic disk cartridge  10  while rotating it along the direction of rotation, the radially inner protrusion  13   a  is positioned so that it is inserted into the second guide portion  4   b . Note that as the height H 2  of the radially outer protrusion  13   b  is higher than the bottom position (depth W 2 ) of the groove of the second guide portion  4   b , there is no possibility that the protrusion  13   b  will be inserted into the second guide portion  4   b.    
     Thus, if the distance of the radially inner protrusion  13   a  from the center point CP differs from that of the radially outer protrusion  13   b , the magnetic disk cartridge  10  can be directed correctly in the inserting direction. Even if the magnetic disk cartridge  10  is formed into the shape of a disk, the cartridge  10  can be reliably loaded in the disk drive  1  so that information can be recorded or reproduced. 
       FIG. 5  shows how the magnetic disk cartridge  10  of  FIG. 4  is inserted into the disk drive  1 . In the magnetic disk cartridge  10  shown in  FIG. 5 , when a portion of the magnetic disk D exposed by the shutter  12  is positioned in an accessible region RA formed near the centerline  3   b  of the disk drive  1 , information can be recorded or reproduced. 
     First, as shown in  FIG. 5A , suppose the case where the magnetic disk cartridge  10  is positioned at the opening  3  of the disk drive  1  and inserted in the direction of arrow B. In this case, the radially inner protrusion  13   a  of the magnetic disk cartridge  10  is brought into contact with the first guide portion  4   a  of the disk drivel. Note that when the radially outer protrusion  13   b  is first inserted into the opening  3  of the disk drive  1 , the radially inner protrusion  13   a  is moved along the first guide portion  4   a , if the user applies force in the direction of arrow R 10 , as described above. 
     If force in the direction of arrow B is applied to the magnetic disk cartridge  10 , the radially inner protrusion  13   a  moves in the direction of arrow A along the curved surface of the first guide portion  4   a . At the same time, the magnetic disk cartridge  10  is inserted into the disk drive  1  while being rotated in the direction of R 10 . Therefore, the angle of the magnetic disk cartridge  10  is adjusted by the first guide portion  4   a . When the radially inner protrusion  13   a  reaches the inlet of the second guide portion  4   b , adjustments to the angle of the magnetic disk cartridge  10  are completed. 
     On the other hand, when the magnetic disk cartridge  10  is flipped and an attempt is made to insert it into the disk drive  1 , the protrusions  13   a  and  13   b  abut the edge portion of the opening  3  of the housing  2 , and consequently, it becomes impossible to insert the magnetic disk cartridge  10  into the opening  3 . In this way, the magnetic disk cartridge  10  is prevented from being inserted when it is flipped over. 
     When the magnetic disk cartridge  10  is inserted into the opening  3 , there are cases where the centerline CL between the protrusions  13   a  and  13   b  crosses the centerline  3   b  of the disk drive  1  at approximately right angles. In such a case, if the user applies force in the direction of arrow R 10 , the radially inner protrusion  13   a  is moved along the first guide portion  4   a , as described above. As a result, the centerline CL between the protrusions  13   a  and  13   b  is aligned with the centerline  3   b  of the disk drive  1 . 
     In the aforementioned case, the magnetic disk cartridge  10  is inserted in the direction of arrow B. However, this description has been made in consideration of the case where with the disk drive  1  held in the left hand, the magnetic disk cartridge  10  is inserted with the index finger of the right hand. Therefore, even when in the state shown in  FIG. 5A  the user applies force in the direction of arrow A, the above-described operation is performed. 
     Next, as shown in  FIG. 5B , the magnetic disk cartridge  10  is moved in the direction of arrow A by the user, and the radially inner protrusion  13   a  is moved to the centerline  3   b  along the second guide portion  4   b . At the same time, within the first guide portion  4   a , the radially outer protrusion  13   b  is moved from the outside of the opening  3  toward the centerline  3   b . If the radially inner protrusion  13   a  reaches the end of the second guide portion  4   b , the movement of the magnetic disk cartridge  10  in the direction of arrow A is stopped. At this time, the radially outer protrusion  13   b  reaches the inlet of the second guide portion  4   b . A portion of the magnetic head D exposed by the shutter  12  is positioned in the region RA of the disk drive  1  where information can be recorded or reproduced. 
     In this manner, the magnetic disk cartridge  10  can be positioned by the protrusions  13   a  and  13   b  and the guide portion  4  so that information can be recorded or reproduced. That is, even in the case where the magnetic disk cartridge  10  is formed into the shape of a disk, the magnetic disk cartridge  10  can be loaded so that the shutter  12  of the magnetic disk cartridge  10  is held at a predetermined position. After the magnetic disk cartridge  10  is loaded in the disk drive  1 , the radially inner protrusion  13   a  is inserted into the second guide portion  4   b , and the radially outer protrusion  13   b  is held in the continuous portion between the first guide portion  4   a  and the second guide portion  4   b . Therefore, rotation of the magnetic disk cartridge  10  is regulated and there is no possibility that the direction of the magnetic disk cartridge  10  will be changed even during loading. 
     Note that the guide  4  shown in  FIG. 5  may alternatively be formed as shown in  FIG. 6 . While the first guide portions  4   a  in  FIG. 5  are provided on both sides of the centerline  3   b , a first guide portion  24   a  may be provided on one side of the centerline  3   b , as in a disk drive  20  of  FIG. 6A . The guide portion  24   a  is continuous with a second guide portion  24   b , which is formed into the shape of a straight line. 
     While the first guide portion  4   a  in  FIG. 5  consists of a curved surface, the first guide portion  34   a  of a disk drive  30  in  FIG. 6B  may be formed into the shape of a taper. The first guide portion  34   a  may be continuous to a second guide portion  34   b.    
     Furthermore, in  FIG. 5 , while a single second guide portion  4   b  is formed along the centerline  3   b , second guide portions  44   b  and  44   b  for projections  13   a  and  13   b  may extend from a first guide portion  44   a , as in a disk drive  40  of  FIG. 6C . In this case, the shutter  12  is provided on a line crossing the centerline CL at approximately right angles. 
       FIG. 7  shows a magnetic disk cartridge  10  constructed in accordance with a second embodiment of the present invention. The magnetic disk cartridge  10  has two openings  11   d  and  11   d , which are formed in the side face  11   c  of a disk housing  11 . The openings  11   d  and  11   d  are disposed at positions shifted 180 degrees, that is, positions facing each other. The openings  11   d  and  11   d  are provided with movable shutters  12  and  12 , respectively. Note that the shutters  12  may be formed from separate members. Alternatively, the shutters  12  may be formed from a single cylindrical member so that they are opened or closed by rotating the single cylindrical member. 
       FIGS. 8A to 8C  are a plan view, a bottom view, and a sectional view of the magnetic disk cartridge  10  shown in FIG.  7 . 
     As shown in  FIG. 8A , protrusions  13 ,  13  are provided on a centerline CL passing through the center point CP of the main surface  11   a  of the housing  11  and are also provided at positions corresponding to the openings  11   d ,  11   d . Since the protrusions  13 ,  13  are provided above the openings  11   d ,  11   d , the wall on each opening  11   d  can be made thicker. Therefore, a reduction in the rigidity of the housing  11  due to the opening  11   d  can be reinforced by the protrusions  13 ,  13 . 
     Note that the protrusions  13 ,  13  may be formed integrally with the housing  11 . Alternatively, they maybe formed separately from the housing  11  and mounted on the housing  11  with an adhesive, etc. The two protrusions  13 ,  13  will be satisfied if they protrude from the main surface  11   a  of the housing  11   
     As shown in  FIG. 8C , the housing  11  has a hollow space  14  for housing a magnetic disk D. The magnetic disk D is held within the housing  11  by a center core  15 . The center core  15  is exposed through a drive hole  16  formed in the bottom surface  11   b  of the housing  11 . If the center core  15  is connected with the spindle of the disk drive  1 , the magnetic disk D held by the center core  15  is rotated. In this way, information is recorded or reproduced. 
       FIGS. 9A and 9B  correspond to  FIGS. 3A and 3B , respectively. The disk drive in  FIG. 9  is the same as that shown in  FIG. 3 . However, the magnetic disk cartridge  10  of  FIG. 9  is provided with two openings  11   d ,  11   d . Therefore, the magnetic disk cartridge  10  of  FIG. 9  differs from that of  FIG. 3  in that two protrusions  13 ,  13  of the same height are disposed at positions of equal distances from the center. 
       FIGS. 10A to 10C  show how the magnetic disk cartridge of  FIG. 8  is inserted into the disk drive, and are plan views that correspond to  FIGS. 5A to 5C , respectively. In the case of  FIG. 10 , the magnetic disk cartridge  10  is provided with two openings  11   d ,  11   d . Therefore, two protrusions  13 ,  13  of the same height are disposed at positions of equal distances from the center. As a result, either of the two openings  11   d  can be positioned in an area RA where information can be recorded or reproduced. 
       FIG. 11A  shows a magnetic disk cartridge and a disk drive constructed in accordance with a third embodiment of the present invention.  FIG. 11B  shows a magnetic disk cartridge and a disk drive constructed in accordance with a fourth embodiment of the present invention. 
     The magnetic disk cartridge  10  shown in  FIG. 11A  is equipped with three openings  11   d  and three shutters  12 . The magnetic disk cartridge  10  further has three protrusions  33   a ,  33   b , and  33   c  on the main surface of a housing  11 . The three openings  11   d  are provided on a first line linking the protrusion  33   a  and the center point CP of the housing  11  together, a second line linking the protrusion  33   b  and the center point CP together, and a third line linking the protrusion  33   c  and the center point CP together, respectively. On the other hand, the guide portion  54  of a disk drive  50  includes a first guide portion  54   a  and two second guide portions  54   b ,  54   b.    
     In the above-described construction, two of the three protrusions  33   a  to  33   c  are inserted into the second guide portions  54   b  and  54   b  even when the magnetic disk cartridge  10  is inserted in the disk drive  50  in either direction. And any one of three openings  11   d  is positioned in a region RA where information can be recorded or reproduced. 
     A magnetic disk cartridge  10  in  FIG. 11B  includes 4 (four) protrusions  43   a  to  43   d  on the main surface of a housing and further includes 4 (four) openings  11   d  and shutters  12 . Each of the 4 openings  11   d  is provided between adjacent protrusions, as shown in  FIG. 11B . 
     In the above-described construction, the two protrusions  43   a  and  43   d  and the two protrusions  43   b  and  43   c  are inserted into the second guide portions  54   b  and  54   b  when the magnetic disk cartridge  10  is inserted in a disk drive  50  in either direction. And any one of 4 (four) openings lid is positioned in a region RA where information can be recorded or reproduced. 
     In accordance with the embodiments shown in  FIGS. 11A and 11B , any one of the openings  11   d  can be positioned in the above-described region RA at all times by cooperation of the guide portions and protrusions, even when the magnetic disk cartridge  10  is inserted into the disk drive at any angle. Thus, the present invention is capable of providing a magnetic disk cartridge which users can employ like a coin. 
     The present invention is not limited to the aforementioned embodiments. In the aforementioned embodiments, the opening  11   d  and the shutter  12  are provided in the side face of the housing  11 . However, as in conventional floppy disks, the openings  11   d  may be formed in the main surfaces. The shutter  12  may be provided to cover the openings  11   d . In this case, protrusions are formed at positions differing from the positions where the openings  11   d  are formed. Even in this case, the magnetic disk cartridge  10  can be positioned in the above-described region RA by cooperation of the protrusions  13 ,  33   a  to  33   c , and  43   a  to  43   d  and the guide portion. 
     In the above-described embodiments, while the protrusions  13 ,  33   a  to  33   c , and  43   a  to  43   d  are provided on the main surface  11   a , they may be provided on the bottom surface  11   b.    
       FIGS. 12 to 15  illustrate a magnetic disk cartridge  10  constructed in accordance with a fifth embodiment of the present invention.  FIG. 12A  shows a perspective view of the magnetic disk cartridge  10 .  FIG. 12B  shows a plan view of the magnetic disk cartridge  10 .  FIG. 13A  shows a sectional view of the magnetic disk cartridge  10 .  FIG. 13B  shows a bottom view of the magnetic disk cartridge  10 .  FIG. 14A  shows an enlarged perspective view of the opening of the magnetic disk cartridge  10 .  FIG. 14B  shows an enlarged sectional view of the opening of the magnetic disk cartridge  10 . 
     As with the above-described embodiments, a housing  11  is formed into the shape of a disk and has an interior space  25  in which a magnetic disk D is rotatably housed. Two openings  11   d ,  11   d  are formed at positions substantially symmetrical with respect to the center point CP of the housing  11 , that is, positions shifted from each other by substantially 180 degrees. At the openings  11   d  and  11   d , shutters  12  are disposed so that they are opened and closed. Note that between  FIGS. 12A and 12B , protrusions  13  are different in shape. 
     As clearly shown in  FIGS. 14A and 14B , this embodiment is characterized in that the opening  11   d  is formed to extend from the side face  11   c  of the housing  11  to the main surface  11   a  of the housing  11 . In the outer edge portion of the main surface  11   a , there is formed a fan-shaped cutout  17  which communicates with the opening  11   d . The protrusion  13  has a larger area than the cutout  17  and is disposed to cover the cutout  17 . 
     While the cutout  17  in  FIG. 14A  is formed into the shape of a fan, the present invention is not limited to this shape. The shape of the cutout  17  is not important if the cutout  17  has a depth such that it does not interfere with a magnetic head holder (slider) which is inserted. 
     As evident in  FIG. 14B , in the case where the opening  11   d  is provided only in the side face of the housing  11 , the height of the opening  11   d  is from the inner bottom surface  11   dn  of the housing  11  to the inner top surface  11   up  of the housing  11 . However, because the above-described cutout  17  is formed, the height of the opening  11   d  is from the inner bottom surface  11   dn  of the housing  11  to the bottom surface of the protrusion  13  and is increased by the thickness W 3  of the upper plate of the housing  11 . Therefore, a wide magnetic head holder (slider) with a plurality of magnetic heads can be inserted into the opening  11   d . As a result, magnetic heads can be positioned over both sides of the magnetic disk D to perform high-density recording. That is, by widening the opening  11   d , the magnetic disk cartridge  10  of a small size and large capacity can be provided. 
     In addition, by covering the cutout  17  with the protrusion  13 , which acts as a reinforcing member, a reduction in the rigidity of the housing  11  due to formation of the opening  11   d  can be compensated for. 
     As shown in  FIGS. 14A and 14B , the opening  11   d  is provided with the shutter  12 . The shutter  12  is movably held by the inner bottom surface  11   dn  of the housing  11  and the protrusion  13 . When the shutter  12  is opened, it is moved in the direction of arrow R 1  along a rail RL formed in the inner top surface  11   up  of the housing  11 . 
     The side face  13   a  of the protrusion  13  must have at least a length that is approximately the same as the length of the opening  11   d , in order to cover the cutout  17 . Because of this, the area of the protrusion  13  is increased. Therefore, even when the magnetic disk cartridge  10  is placed on a desk or floor with the main surface  11   a  downward, the magnetic disk cartridge  10  is stable. 
       FIGS. 15A and 15B  correspond to  FIGS. 9A and 9B , respectively. In  FIG. 15 , the second guide portion  4  of the disk drive  1  is widened to correspond to the increased area of the protrusion  13 . Since the remaining construction is the same as that of  FIG. 9 , a detailed description will not be given to avoid redundancy. Even in the case where either protrusion  13  is first inserted into the disk drive  1 , either opening  11   d  is reliably positioned in the above-described recording region RA, because the two openings  11   d  and the shutters  12  are disposed near the protrusions  13 . 
     As described above, the cutout  17 , which communicates with the opening  11   d , is formed in the main surface  11   a  of the housing  11 , and the opening  11   d  is formed between the bottom surface of the protrusion  13  and the inner bottom surface  11   dn  of the housing  11 . In this way, the height of the opening  11   d  of the housing  11  can be increased. Therefore, a thick magnetic head holder (slider) with two magnetic heads, for example, can be inserted into the widened opening  11   d . As a result, high-density recording can be performed on the magnetic disk cartridge  10  and therefore the magnetic disk cartridge  10  with a large recording capacity can be provided. 
     In the above-described embodiments, the protrusion  13  has a generally circular or elliptical planar shape. However, in the planar shape of the protrusion  13 , the side face  13   a  has to correspond to the R-shape of the opening  11   d , but the shape of a portion other than the side face  13   a  is not important. In addition, although the protrusions  13 ,  13  are provided on the main surface  11   a  of the housing  11 , they may be provided on the bottom surface  11   b  of the housing  11 . 
     In the above-described embodiments, the magnetic disk cartridge  10  has a plurality of protrusions on the main surface  11   a  of the generally disk-shaped housing  11 . When the magnetic disk cartridge  10  is loaded in a disk drive, the cartridge  10  is positioned in a direction capable of recording and reproduction by cooperation of the protrusions of the cartridge  10  and the guide portion of the disk drive. However, in the embodiment depicted in  FIGS. 16 and 17 , the generally disk-shaped housing of a magnetic disk cartridge  10  has a guide groove  60 . When the magnetic disk cartridge  10  is loaded in a disk drive, the cartridge  10  is positioned in a direction capable of recording and reproduction by cooperation of the guide groove  60  of the cartridge  10  and a protrusion  62  formed within the slot S of the disk drive. 
     That is,  FIG. 16A  shows a perspective view of the bottom of the magnetic disk cartridge  10  constructed in accordance with a sixth embodiment of the present invention.  FIG. 16B  shows an enlarged perspective view of the slot S of the disk drive  1  in which the magnetic disk cartridge of  FIG. 16A  is loaded.  FIG. 17  shows the state in which the magnetic disk cartridge  10  is loaded in the disk drive  1 . 
     The magnetic disk cartridge  10  has a generally disk-shaped housing  11 , a magnetic disk D rotatably housed in the space of the housing  11 , and a movable shutter  12  for covering the generally V-shaped openings  11   d  of the housing  11 . The housing  11  is molded from resin, etc. The V-shaped openings  11   d  are formed in both sides of the housing  11  having a thickness of t. The V-shaped openings  11   d  are provided with a rotatable shutter  12  having a thickness thinner than the thickness t of the housing  11 . That is, the shutter  12  is rotatable in the direction of arrow R 2  along the circumference of the housing  11  between a closing position shown in  FIG. 16A  and an opening position at which the magnetic disk D is exposed. 
     The bottom surface of the housing  11  has a guide groove  60 , which extends along the diameter of the housing  11 . Near the opening  11   d , the guide groove  60  consists of a broad portion  60   a  which widens toward the outer edge of the housing  11 , and a guide portion  60  which extends linearly from the broad portion  60   a . In the intermediate portion of the guide portion  60 , that is, the center portion of the housing  11 , there is provided a drive hole  16  into which the spindle (not shown) of the disk drive  1  for driving the magnetic disk D is inserted. The rearmost end of the guide groove  60  is terminated by the wall  60   c  of the housing  11 . This wall  60   c  is not always required. The wall  60   c  may be formed integrally with the housing  11 , or it may be a separate member. 
     The disk drive  1  into which the magnetic disk cartridge  10  is inserted has a slot S in the side face  61 , as shown in  FIG. 16B . The slot S has a width T that is slightly greater than the thickness t of the magnetic disk cartridge  10 , and also has a depth that is slightly longer than the diameter of the housing  11 . In the longitudinal central portion of the slot S along the side face  61 , there is provided a protruding portion  62  that extends in the direction where the magnetic disk cartridge  10  is inserted. Near the inlet of the slot S, the protruding portion  62  has an end face  62   a  at a position recessed from the inlet by a distance slightly greater than the radial thickness of the wall  60   c  of the housing  11 . The protruding portion  62  also has a length equal to the distance from the wall  60   c  to the drive hole  16  of the magnetic disk cartridge  10 . 
     Next, the manner in which the magnetic disk cartridge  10  is inserted into the disk drive  1  will be described with reference to  FIG. 17 . The broad portion  60   a  of the guide groove  60  of the magnetic disk cartridge  10  is roughly aligned with the protruding portion (shaded portion)  62  of the disk drive  1  and is inserted into the slot S. As described above, the broad portion  60   a  widens toward the outer edge of the housing  11 . Therefore, even if the guide groove  60  is slightly shifted laterally from the protruding portion  62 , the guide groove  60  is positioned so that the protruding portion  62  is inserted into the guide groove  60 . Furthermore, if the magnetic disk cartridge  10  is pushed into the slot S in the direction of arrow C, the magnetic disk cartridge  10  is inserted smoothly into the slot S while being guided by the protruding portion  62 . The end face  62   a  of the protruding portion  62  may be a curved face so that it is easily inserted into the guide groove  60 , or the end portion of the protruding portion  62  may be formed into the shape of a wedge. 
     If the protruding portion  62  becomes longer, the magnetic disk cartridge  10  can be more stably guided. If the magnetic disk cartridge  10  is inserted completely into the slot S, the end face  62   a  of the protruding portion  62  is positioned near the wall  60   c  of the magnetic disk cartridge  10 . At this position, the shutter  12  is opened within the disk drive  1  by a shutter opening mechanism (not shown), and information can be recorded on or reproduced from the magnetic disk D by a magnetic head (not shown). 
     Thus, the magnetic disk cartridge  10  is guided and inserted by cooperation of the guide groove  60  and the protruding portion  62 . In this case, the outer periphery of the magnetic disk cartridge  10  contacts the slot S at only a slight portion. In other words, since the magnetic disk cartridge  10  and the slot S are in a relationship of a circle and a tangential line, there is no possibility that the magnetic disk cartridge  10  and the slot will interfere with each other at the time of insertion. In addition, the magnetic disk cartridge  10  can be manufactured at low cost because it is structurally simple. For instance, if the magnetic disk cartridge  10  is used as a recording medium for digital cameras, information recorded on the magnetic disk cartridge  10  can be given away to a person. 
     In the case where a portion of the magnetic disk cartridge  10  other than the broad portion  60   a  is inserted into the slot S, the outer periphery of the housing  11  abuts the end face  62   a  of the protruding portion  62  and therefore incorrect insertion can be prevented. Since the guide groove  60  is formed only in one side of the magnetic disk cartridge  10 , the top surface or bottom surface of the magnetic disk cartridge  10  can be confirmed before it is inserted. As a result, incorrect insertion can be prevented. 
     When the magnetic disk cartridge  10  is taken out from the disk drive  1 , it can be ejected by a discharge mechanism (not shown) provided in the disk drive  1 , as in the case of conventional floppy disks. 
     While the magnetic disk cartridge  10  with the guide groove  60  has been described, the present invention is not limited to this embodiment, but may be modified. For example, if the protruding portion  62  has a bore into which the above-described spindle is inserted, the protruding portion  62  can be extended over the diameter of the magnetic disk cartridge  10 . In this case, the magnetic disk cartridge  10  can be prevented from being shifted in the longitudinal direction of the slot S at the time of insertion. Thus, the magnetic disk cartridge  10  can be more stably guided. 
       FIG. 18  shows a magnetic disk cartridge constructed in accordance with a seventh embodiment of the present invention. In this embodiment and subsequent embodiments, the same reference numerals will be applied to the same parts as the above-described embodiments and therefore a description thereof will not be given. 
     In a magnetic disk cartridge  110  shown in  FIGS. 18A and 18B , the structure of a protrusion differs, for example, from that of the magnetic disk cartridge  10  shown in  FIG. 4 . That is, a single broad protrusion  113  is provided on the main surface  11   a  of a housing  11  along the outer circumference of the housing  11 . The broad protrusion  113  has a arcuate face  113   a  so that users can hold it with the fingers. 
       FIG. 18C  shows a disk drive  100  into which the magnetic disk cartridge  110  is inserted. The housing of the disk drive  100  has a guide portion  74 , which is equipped with a arcuate face  74   a  corresponding to the shape of the arcuate face  113   a  of the protrusion  113  of the housing  11  of the magnetic disk cartridge  110 . 
     In this case, when the magnetic disk cartridge  110  is loaded in the disk drive  100 , the user holds the protrusion  113  with the fingers and inserts it into the opening  3  of the disk drive  100 . When the protrusion  113  is not positioned within the guide portion  74 , the magnetic disk cartridge  110  cannot be loaded in the disk drive  100 . In this way, the magnetic disk cartridge  110  is inserted into the disk drive  100  in a direction capable of recording and reproduction. 
     That is, if the magnetic disk cartridge  110  is inserted into the disk drive  100  in the direction of arrow A by the user, the protrusion  113  is inserted into the guide portion  74 , as shown in  FIGS. 19A and 19B . The arcuate face  113   a  of the protrusion  113  is engaged with the arcuate face  74   a  of the guide portion  74 , whereby the movement of the magnetic disk cartridge  110  in the direction of arrow A is regulated. In this way, the magnetic disk cartridge  110  is held at a position capable of recording and reproduction with respect to the disk drive  100 . Therefore, even in the case where the magnetic disk cartridge  110  is formed into the shape of a disk, the magnetic disk cartridge  110  can be reliably positioned with respect to the disk drive  100  in a direction capable of recording and reproduction. When the magnetic disk cartridge  110  is loaded in the disk drive  100 , the arcuate face  113   a  of the protrusion  113  is engaged with the arcuate face  74   a  of the guide portion  74 , and consequently, there is no possibility that the magnetic disk cartridge  110  will be shifted. 
       FIG. 20A  shows a plan view of a magnetic disk cartridge  120  constructed in accordance with an eighth embodiment of the present invention.  FIG. 20B  shows a side view of the magnetic disk cartridge  120  shown in  FIG. 20A .  FIG. 20C  shows a sectional view of the magnetic disk cartridge  120  shown in  FIG. 20A . 
     The magnetic disk cartridge  120  has a protruding piece  123  at the outer edge of the circular main surface  121   a . The protruding piece  123  is rotatable through 180 degrees in the direction of arrow R 20  shown in  FIG. 20C . The main surface  121   a  has a housing groove  124  for housing the protruding piece  123 . For example, when the magnetic disk cartridge  120  is put in a pocket and carried, the protruding piece  123  is housed in the housing groove  124 . In this way, the protruding piece  123  can be prevented from being disengaged from the housing  121 . 
     On the other hand, when the magnetic disk cartridge  120  is inserted into the disk drive, the protruding piece  123  is pulled up 180 degrees and protruded from the side face  121   c  of the housing  121 . In this way, the user can recognize the inserting direction of the magnetic disk cartridge  120  with the sense of touch by the protruding piece  123 . In addition, when the magnetic disk cartridge  120  is taken out from the disk drive, the user can also pull the protruding piece  123  out of the housing groove  124  with the fingers. 
     The main surface  121   a  of the housing  121  has an arcuate recess  125  in the vicinity of the protruding piece  123 . With this arcuate recess  125 , the user can also recognize the inserting direction of the magnetic disk cartridge  120  by the sense of touch and can easily hold the magnetic disk cartridge  120 . Note that the main surface  121   a  may have a generally circular recess  125 A such as that shown in  FIG. 21 . 
     Furthermore, the protruding piece  123  may have a bore  123   a  such as that shown in  FIG. 22A . If a string RP is passed through the bore  123   a , the magnetic disk cartridge  120  can be hung round the user&#39;s neck and carried. As shown in  FIGS. 22B and 22C , if a string RP is passed through the bores  123   a  of a plurality of the magnetic disk cartridges  120 , they can be carried. As a result, the convenience can be enhanced. 
     As shown in  FIGS. 23A to 23C , in the case where magnetic disk cartridges  120  are put in a housing case  130  and carried, a pin  131  in the housing case  130  is passed through the bores  123   a  of the protruding pieces  123  of the magnetic disk cartridges  120 . In this way, the housed magnetic disk cartridges  120  can be prevented from being moved within the housing case  130 . Therefore, the shock resistance of the housing case  130  is enhanced. The housing case  130  has a cartridge housing portion and a lid rotatably attached to the cartridge housing portion. The above-described protruding piece  123  may be attached to the main surface  121   a  or side face of the housing  120 . 
       FIGS. 24 to 30  illustrate magnetic disk cartridges and disk drives with various shapes and structures. 
       FIGS. 24A to 24C  show a magnetic disk cartridge  140  constructed in accordance with a ninth embodiment of the present invention. The magnetic disk cartridge  140  is equipped with a film-shaped protruding piece  143 , which protrudes from the side face  141   a  of a housing  141 . When the magnetic disk cartridge  140  is taken out from a disk drive, a user can pull it out of the disk drive while holding the protruding piece  143 . 
       FIGS. 25A and 25B  show a magnetic disk cartridge  150  constructed in accordance with a tenth embodiment of the present invention. The housing  151  of the magnetic disk cartridge  150  has a front curved edge  150   a  that is inserted into a disk drive, and a rear straight edge  150   b.    
     If a magnetic disk cartridge shown in  FIG. 26A  or  26 B is inserted into a disk drive  160  shown in  FIG. 26C , a portion of the magnetic disk cartridge is exposed through the cutout  161  of the disk drive  160 , as shown in  FIG. 27 . Therefore, a user can hold the magnetic disk cartridge through the cutout  161  with fingers and take it out of the disk drive  160 . 
       FIGS. 28A to 28D  show disk drives equipped with housings that have various cutouts. The main surface of each housing may have an arrow indicative of a direction where the disk drive with a magnetic disk cartridge loaded therein is inserted into the slot of electronic equipment. 
       FIGS. 29 and 30  show the shape of the housing of each of various magnetic disk cartridges, and the shape of a corresponding disk drive into which the magnetic disk cartridge is inserted. 
       FIGS. 31A to 31I  show various shapes of magnetic disk cartridge housings. 
     While the present invention has been described with reference to the preferred embodiments thereof, the invention is not to be limited to the details given herein, but may be modified within the scope of the invention hereinafter claimed.