BACKGROUND 
     1. Technical Field 
     The present disclosure relates to an electronic device with a fan. 
     2. Description of Related Art 
     A fan is provided in an electronic device for cooling electronic components. However, the fan can be incorrectly installed if care is not taken during the installation. Therefore, there is room for improvement in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the embodiments. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is an exploded, isometric view of an electronic device in accordance with an embodiment. 
         FIG. 2  is similar to  FIG. 1 , but viewed from a different aspect. 
         FIG. 3  is a cross-sectional view of the fan module of  FIG. 1  along the line A-A. 
         FIG. 4  is a view of the assembled device of  FIG. 1 . 
         FIG. 5  is a cross-sectional view taken along the line B-B in  FIG. 4 , and shows the fan module correctly assembled. 
         FIG. 6  is similar to  FIG. 5 , but shows the fan module placed in an opposite direction and incorrectly assembly. 
         FIG. 7  is a view of an assembled electronic device in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
     Referring to  FIG. 1 , an electronic device in accordance with one embodiment includes a fan module  10  and a cage  30 . 
     The fan module  10  includes a bracket  13  and a fan  11 . The bracket  13  includes a body  133 , a first sidewall  131 , and a second sidewall  135 . The first and second sidewalls  131 ,  135  are located on opposite sides of the body  133 . A holding space  1353  is defined in the bracket  13  through the first sidewall  131 , the body  133 , and the second sidewall  135 . A plurality of first mounting holes  1311  is defined in the first sidewall  131 . A plurality of second mounting holes  1351  is defined in the second sidewall  135 . Referring to  FIG. 2 , a mounting portion  1313  is located in the holding space  1353  and connected to the plate  31 . A first distance D 1  (shown in  FIG. 3 ) is defined between the outer surface of the mounting portion and the outer surface of the first sidewall. In one embodiment, the outer surface of the mounting portion is aligned with the outer surface of the first sidewall, and the distance D 1  is approximately equal to zero. 
     The fan  11  is received in the holding space  1353  and includes a motor  113  and a plurality of blades  115  located on the shaft of the motor  113 . The motor  113  is secured to the mounting portion  1313 . A second distance D 2  (shown in  FIG. 3 ) is defined between the outer surface of the motor and the outer surface of the second sidewall. 
     Referring to  FIG. 1 , the cage  30  includes a mounting plate  31  and a flange  33  located on the mounting plate  31 . A ventilation hole  315  is defined in the mounting plate  31 . A positioning portion  313  is located in the ventilation hole  315  and connected to the mounting plate  31 . In an embodiment, the positioning portion  313  includes a base  3133  and four fingers  3131  connected to the mounting plate  31 , with each finger  3131  being substantially perpendicular to an adjacent finger  3131 . A restriction  319 , such as a simple nub or boss, is located on the inner surface of the positioning portion. A height H (shown in  FIG. 6 ) of the restriction  319  relative to the inner surface of the positioning portion is defined, and the height H is greater than the first distance D 1 , but less than the second distance D 2 . A plurality of securing holes  317  is defined in the mounting plate  31  around the ventilation hole  315 , corresponding to the first and second mounting holes  1311 ,  1351 . Two locking holes  331  are defined in the flange  33 . An ear  35  is located on the mounting plate  31 , and an installing hole  351  is defined in the ear  35 . In one embodiment, the ear  35  and the flange  33  are substantially perpendicular to one another, on two edges of the mounting plate  31  which adjoin. 
     Referring also to  FIG. 4  and  FIG. 5 , in assembly, if the second sidewall  135  is placed on the inner surface of the positioning portion, because the height H of the restriction  319  is less than the second distance D 2 , the restriction  319  does not abut the outer surface of the mounting portion when the fan module  10  is placed on the mounting plate  31 . In this situation, the fan module  10  is correctly placed on the cage  30 . The outer surface of the second sidewall abuts the mounting plate  31 , and the second mounting holes  1351  are aligned with the securing holes  317 . A plurality of first fasteners, such as screws, may be used to secure the fan module  10  to the mounting plate  31 . 
     Referring also to  FIG. 6 , if the first sidewall  131  of the fan module  10  is placed on the inner surface of the positioning portion, because the distance H of the restriction  319  is greater than the first distance D 1 , the restriction  319  abuts the outer surface of the mounting portion when the fan module  10  is placed on the mounting plate  31 . The rocking and general instability of the fan module  10  in this situation indicates that the module  10  is incorrectly placed on the cage  30 . 
     Referring to  FIG. 7 , the cage  30  is secured to a computer enclosure  50 . The computer enclosure  50  includes a bottom plate  51  and a side plate  53  substantially perpendicular to the bottom plate  51 . A power supply cage  60  is secured to the side plate  53 . A second fastener, such as a screw, is engaged in the installing hole  351  and a fixing hole defined in the side plate  53 , to secure the cage  30  to the inner surface of the side plate. 
     After the fan module  10  and the cage  30  are secured to the computer enclosure  50 , the mounting plate  31  is substantially perpendicular to the side plate  53  and substantially parallel to the bottom plate  51 . The flange  33  is substantially perpendicular to the side plate  53  and the bottom plate  51 . The ear  35  is secured to the side plate  53 . The first and second sidewalls  131 ,  135  are substantially perpendicular to the mounting plate  31 . 
     It is to be understood, however, that even though numerous characteristics and advantages have been set forth in the foregoing description of embodiments, together with details of the structures and functions of the embodiments, the disclosure is illustrative only and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of the disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
An electronic device includes a cage and a fan module. The cage includes a mounting plate defining a ventilation hole. A positioning portion is located in the ventilation hole. A restriction is located on an inner surface of the positioning portion. The height of the restriction is such as to strictly require the fan module to be in the correct orientation when it is fitted to the electronic device.