Patent Publication Number: US-8995143-B2

Title: Pivotal assembly applied to board

Description:
RELATED APPLICATIONS 
     This application claims priority to China Application Serial Number 201210455085.3, filed Nov. 14, 2012, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The invention relates to a pivotal assembly applied to a board. More particularly, the invention relates to a pivotal assembly applied to a riser board for inserting memory modules in a computer system. 
     2. Description of Related Art 
     In existing computer systems, the memory module, such as a Dual In-line Memory Module (DIMM), is generally plugged directly into memory sockets of a motherboard. However, in order to use more memory modules in a server, a riser board is used to augment the number of the memory modules. In all of the current approaches, a plurality of memory modules are plugged onto a single riser board to form a memory combination, and then the whole memory combination is plugged into a riser slot on the motherboard. A control chip is configured on the riser board for controlling reading data from and writing data to various memory modules on the riser board. 
     However, the current techniques for plugging a plurality of riser boards into the motherboard all enable the memory modules on each riser board to face toward the same direction and the riser boards are arranged closely. Nonetheless, it is inevitable that the control chip configured on the riser board occupies a portion of the space on the riser board, and thus the memory sockets cannot be configured in that occupied space, so that the space between two riser boards corresponding to the control chip is unused, not being utilized efficiently. Therefore, in the case that the height and space of the server are limited, how to place more memory modules in the limited space is a challenge to those in the art. 
     SUMMARY 
     The invention provides a pivotal assembly applied to a board, which includes a first board, a first pivotal member, and a pivotal plate. The first pivotal member is fixed to the first board and has a first retaining structure. The pivotal plate is pivotally connected to the first pivotal member and has a first protrusion. The first protrusion is retained in the first retaining structure, so as to make the first board limitedly rotate to be perpendicular or parallel to the pivotal plate. 
     In an embodiment of the invention, the abovementioned first pivotal member includes a first fixing portion, a first pivotal portion, and a first pivotal axis. The first fixing portion is fixed to the first board. The first pivotal portion is connected to the first fixing portion and bent relative to the first fixing portion. The first pivotal axis is pivotally connected to the inner wall of the first pivotal portion. 
     In an embodiment of the invention, the abovementioned pivotal plate includes a main body and two second pivotal portions. The second pivotal portions are connected to the main body and are bent relative to the main body. The first pivotal portion is arranged between the second pivotal portions side by side. The first pivotal axis is further pivotally connected to the inner walls of the second pivotal portions. 
     In an embodiment of the invention, the abovementioned first retaining structure is located on the first pivotal portion. The first protrusion is connected to the main body and extends into the first retaining structure. The first retaining structure has a first retaining edge and a second retaining edge opposite to each other. During rotation of the first board relative to the pivotal plate, the first protrusion is limitedly moved between the first retaining edge and the second retaining edge. 
     In an embodiment of the invention, the abovementioned first retaining edge is adjacent to the end of the first pivotal portion that is connected to the first fixing portion. The second retaining edge is adjacent to the end of the first pivotal portion that is away from the first fixing portion. When the first board rotates relative to the pivotal plate to make the first protrusion abut against the first retaining edge, the first board is parallel to the pivotal plate. When the first board rotates relative to the pivotal plate to make the first protrusion abut against the second retaining edge, the first board is perpendicular to the pivotal plate. 
     In an embodiment of the invention, the abovementioned pivotal plate further has a second protrusion. The first protrusion and the second protrusion are respectively located at two ends of the pivotal plate. The pivotal assembly applied to the board further includes a second board and a second pivotal member. The second pivotal member is fixed to the second board and has a second retaining structure. The first pivotal member and the second pivotal member are pivotally connected to two ends of the pivotal plate, respectively. The second protrusion is retained in the second retaining structure, so as to make the second board limitedly rotate to be perpendicular or parallel to the pivotal plate. When both of the first board and the second board are perpendicular to the pivotal plate, the first board and the second board are located face to face. 
     In an embodiment of the invention, the abovementioned second pivotal member includes a second fixing portion, a third pivotal portion, and a second pivotal axis. The second fixing portion is fixed to the second board. The third pivotal portion is connected to the second fixing portion and is bent relative to the second fixing portion. The second pivotal axis is pivotally connected to the inner wall of the third pivotal portion. 
     In an embodiment of the invention, the abovementioned pivotal plate includes a main body and two fourth pivotal portions. The fourth pivotal portions are connected to the main body and are bent relative to the main body. The third pivotal portion is arranged between the fourth pivotal portions side by side, and the second pivotal axis is further pivotally connected to the inner walls of the fourth pivotal portions. 
     In an embodiment of the invention, the abovementioned second retaining structure is located on the third pivotal portion. The second protrusion is connected to the main body and extends into the second retaining structure. The second retaining structure has a third retaining edge and a fourth retaining edge opposite to each other. During rotation of the second board relative to the pivotal plate, the second protrusion is limitedly moved between the third retaining edge and the fourth retaining edge. 
     In an embodiment of the invention, the abovementioned third retaining edge is adjacent to the end of the second pivotal portion that is connected to the second fixing portion. The fourth retaining edge is adjacent to the end of the second pivotal portion that is away from the second fixing portion. When the second board rotates relative to the pivotal plate to make the second protrusion abut against the third retaining edge, the second board is parallel to the pivotal plate. When the second board rotates relative to the pivotal plate to make the second protrusion abut against the fourth retaining edge, the second board is perpendicular to the pivotal plate. 
     In view of the above, an essential feature of the invention is that two boards of the pivotal assembly are pivotally connected to the pivotal plate, respectively, through two pivotal members, so that the two boards can to be unfolded and folded like a book. Another essential feature of the invention is that the two pivotal members, respectively, have a retaining structure for retaining the corresponding protrusion configured on the pivotal plate, so that the a distance between two riser boards can be maintained when the two boards are folded to each other, thereby avoiding collision of the two boards. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a pivotal assembly applied to board according to an embodiment of the invention; 
         FIG. 2  is a perspective view illustrating a pivotal assembly applied to board according to another embodiment of the invention; 
         FIG. 3  is a perspective view illustrating a computer system according to an embodiment of the invention; 
         FIG. 4  is an unfolded view illustrating a memory combination according to an embodiment of the invention; 
         FIG. 5A  is a perspective view illustrating the memory combination of  FIG. 4  after being folded and before being plugged to a motherboard in the computer system; 
         FIG. 5B  is a perspective view illustrating the memory combination in  FIG. 5A  after being plugged to the motherboard; 
         FIG. 6  is a partial exploded view illustrating the memory combination in  FIG. 5A ; and 
         FIG. 7  is another partial exploded view illustrating the memory combination in  FIG. 5A . 
     
    
    
     DETAILED DESCRIPTION 
     A plurality of embodiments of the invention will be disclosed hereafter with reference to drawings. For purposes of clear illustration, many details in practice will be described together in the disclosure. However, it should be understood that these details in practice are not intended to limit the invention. That is, in some embodiments of the invention, these details in practice are unnecessary. Additionally, for purposes of simplifying drawings, some conventional structures and elements in the drawings will be illustrated schematically 
       FIG. 1  illustrates a perspective view of a pivotal assembly  1  applied to board according to an embodiment of the invention. 
     As shown in  FIG. 1 , in this embodiment, the pivotal assembly  1  applied to board includes a board  10 , a pivotal member  12 , and a pivotal plate  14 . The pivotal member  12  is fixed to the board  10  and has a retaining structure  120 . The pivotal plate  14  is pivotally connected to the pivotal member  12  and has a protrusion  140 . The protrusion  140  is retained in the retaining structure  120 , so as to make the board  10  limitedly rotate to be perpendicular or parallel to the pivotal plate  14 . 
       FIG. 2  illustrates a perspective view of a pivotal assembly  3  applied to a board according to another embodiment of the invention. 
     As shown in  FIG. 2 , the pivotal assembly  3  applied to a board includes a first board  30 , a first pivotal member  32 , a pivotal plate  34 , a second board  36 , and a second pivotal member  38 . The first pivotal member  32  is fixed to the first board  30  and has a first retaining structure  320 . The pivotal plate  34  is pivotally connected to the first pivotal member  32  and has a first protrusion  340 . The first protrusion  340  is retained in the first retaining structure  320 , so as to make the first board  30  limitedly rotate to be perpendicular or parallel to the pivotal plate  34 . 
     Additionally, the pivotal plate  34  further has a second protrusion  342 . The first protrusion  340  and the second protrusion  342  are respectively located at two ends of the pivotal plate  34 . The second pivotal member  38  is fixed to the second board  36  and has a second retaining structure  380 . The first pivotal member  32  and the second pivotal member  38  are pivotally connected to two ends of the pivotal plate  34 , respectively. The second protrusion  342  is retained in the second retaining structure  380 , so as to make the second board  36  limitedly rotate to be perpendicular or parallel to the pivotal plate  34 . Moreover, when both of the first board  30  and the second board  36  are perpendicular to the pivotal plate  34 , the first board  30  and the second board  36  are located face to face. 
     It should be noted that the detailed structure and operation manner relating to the board  10 , the pivotal member  12 , and the pivotal plate  14  in  FIG. 1 , as well as the detailed structure and operation manner relating to the first board  30 , first pivotal member  32 , pivotal plate  34 , second plate  36 , and second pivotal member  38  in  FIG. 2 , can become apparent from embodiments relating to the memory combination illustrated in  FIGS. 3-7  hereafter. 
       FIG. 3  illustrates a perspective view of a computer system  5  according to an embodiment of the invention. 
     In  FIG. 3 , the computer system  5  of this embodiment is exemplified as a server, although the invention is not limited to such. For any computer system  5 , as long as it is required to plug many memory modules into the motherboard in the computer system  5 , the concept of the memory combination of the invention can be applied to effectively enhance the space utilization inside a housing  50  of the computer system  5 . 
       FIG. 4  is an unfolded view illustrating the memory combination according to an embodiment of the invention.  FIG. 5  is a perspective view illustrating the memory combination in  FIG. 4  after being folded and before being plugged to a motherboard  52  in the computer system  5 .  FIG. 5B  is a perspective view illustrating the memory combination in  FIG. 5A  after being plugged to the motherboard  52 . 
     As shown in  FIG. 4 , in this embodiment, the memory combination includes a first riser board  54 , a first pivotal member  60 , a second riser board  56 , a second pivotal member  62 , and a pivotal plate  58 . The first pivotal member  60  is fixed to the first riser board  54 . The second pivotal member  62  is fixed to the second riser board  56 . Two ends of the pivotal plate  58  are pivotally connected to the first pivotal member  60  and the second pivotal member  62 , respectively. 
     It should be noted that, in this embodiment, the first riser board  54  corresponds to the board  10  in  FIG. 1  and the first board  30  in  FIG. 2 , while the second riser board  56  corresponds to the board  10  in  FIG. 1  and the second board  36  in  FIG. 2 . 
     The first riser board  54  of the memory combination includes a plurality of first memory sockets  540 . The second riser board  56  includes a plurality of second memory sockets  560 . The first memory sockets  540  on the first riser board  54  and the second memory sockets  560  on the second riser board  56  are all used to plug the memory module  64 . For example, the memory module  64  may be a Dual In-line Memory Module (DIMM), but the invention is not limited to such. 
     Additionally, the first pivotal member  60  has a first retaining structure, and the second pivotal member  62  has a second retaining structure. The pivotal plate  58  has a first protrusion  584  and a second protrusion  588 . The first protrusion  584  and the second protrusion  588  are respectively located at two ends of the pivotal plate  58 . The first protrusion  584  of the pivotal plate  58  is retained in the first retaining structure, so as to make the first riser board  54  limitedly rotate relative to the pivotal plate  58  to be optionally perpendicular or parallel to the pivotal plate  58 . The second protrusion  588  of the pivotal plate  58  is retained in the second retaining structure, so as to make the second riser board  56  limitedly rotate relative to the pivotal plate  58  to be optionally perpendicular or parallel to the pivotal plate  58 . 
     In this way, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , the invention can enable the first memory sockets  540  on the first riser board  54  to face the second riser board  56 , and enable the second memory sockets  560  on the second riser board  56  to face the first riser board  54  (i.e., with an appearance as a folded book). 
     In order to achieve the operation that the first riser board  54  and the second riser board  56  are perpendicular or parallel to the pivotal plate  58 , the detailed structure relating to the first pivotal member  60 , the second pivotal member  62  and the pivotal plate  58  will be further described in details hereafter. 
       FIG. 6  illustrates a partial exploded view of the memory combination in  FIG. 5A . 
     As shown in  FIG. 6 , in this embodiment, the first pivotal member  60  includes a first fixing portion  600 , a first pivotal portion  602  and a first pivotal axis  604 . The first fixing portion  600  of the first pivotal member  60  is fixed to the first riser board  54 . The first pivotal portion  602  of the first pivotal member  60  is connected to the first fixing portion  600  and bent relative to the first fixing portion  600 . The first pivotal axis  604  of the first pivotal member  60  is pivotally connected to the inner wall of the first pivotal portion  602 . 
     Additionally, the pivotal plate  58  includes a main body  580  and two second pivotal portions  582 . The second pivotal portions  582  of the pivotal plate  58  are connected to the main body  580  and bent relative to the main body  580 . The first pivotal axis  604  is further pivotally connected to the inner walls of the second pivotal portions  582 . In other words, the first pivotal portion  602  of the first pivotal member  60  and two second pivotal portions  582  of the pivotal plate  58  are all pivotally connected to the first pivotal axis  604 , so that the first riser board  54  and the pivotal plate  58  can rotate relative to each other. 
     Moreover, in this embodiment, the first pivotal portion  602  of the first pivotal member  60  is arranged between the second pivotal portions  582  of the pivotal plate  58  side by side. Through this structure configuration it can be prevented that the first pivotal portion  602  departs from the second pivotal portions  582  along the axial direction of the first pivotal axis  604 . 
     Also shown in  FIG. 6 , in this embodiment, the first retaining structure  606  of the first pivotal member  60  is a slotted hole. The first retaining structure  606  is located on the first pivotal portion  602 . The first protrusion  584  of the pivotal plate  58  is connected to the main body  580 , located between the second pivotal portions  582  and extends into the first retaining structure  606 . The first retaining structure  606  has a first retaining edge  606   a  and a second retaining edge  606   b  opposite to each other. During rotation of the first riser board  54  relative to the pivotal plate  58  (that is, during rotation of the first pivotal portion  602  and the two second pivotal portions  582  relative to the first pivotal axis  604 ), the first protrusion  584  is limitedly moved between the first retaining edge  606   a  and the second retaining edge  606   b.    
     Furthermore, the first retaining edge  606   a  of the first retaining structure  606  is adjacent to the end of the first pivotal portion  602  connected to the first fixing portion  600 . The second retaining edge  606   b  of the first retaining structure  606  is adjacent to the end of the first pivotal portion  602  away from the first fixing portion  600 . When the first riser board  54  rotates relative to the pivotal plate  58  to make the first protrusion  584  abut against the first retaining edge  606   a , the first riser board  54  is parallel to the pivotal plate  58 . When the first riser board  54  rotates relative to the pivotal plate  58  to make the first protrusion  584  abut against the second retaining edge  606   b , the first riser board  54  is perpendicular to the pivotal plate  58 . 
     However, the shape of the first retaining structure of the invention is not limited to the form of slotted hole. In another embodiment, the first retaining structure also may be a groove (not shown) formed at a side edge of the first pivotal portion  602 , and the first protrusion  584  is correspondingly configured at the side edge of the second pivotal portion  582  and extends into the abovementioned groove, so as to make the first riser board  54  limitedly rotate relative to the pivotal plate  58  as well. 
       FIG. 7  illustrates another partial exploded view of the memory combination in  FIG. 5A . 
     As shown in  FIG. 7 , in this embodiment, the second pivotal member  62  includes a second fixing portion  620 , a third pivotal portion  622 , and a second pivotal axis  624 . The second fixing portion  620  of the second pivotal member  62  is fixed to the second riser board  56 . The third pivotal portion  622  of the second pivotal member  62  is connected to the second fixing portion  620  and bent relative to the second fixing portion  620 . The second pivotal axis  624  of the second pivotal member  62  is pivotally connected to the inner wall of the third pivotal portion  622 . 
     Additionally, the pivotal plate  58  further includes two fourth pivotal portions  586 . The fourth pivotal portions  586  of the pivotal plate  58  are connected to the main body  580  and bent relative to the main body  580 . The second pivotal axis  624  is further pivotally connected to the inner walls of the fourth pivotal portions  586 . In other words, the third pivotal portion  622  of the second pivotal member  62  and the two fourth pivotal portions  586  of the pivotal plate  58  are all pivotally connected to the second pivotal axis  624 , so that the second riser board  56  and the pivotal plate  58  can rotate relative to each other. 
     Moreover, in this embodiment, the third pivotal portion  622  of the second pivotal member  62  is arranged between two fourth pivotal portions  586  of the pivotal plate  58  side by side. Through this structure configuration it can be prevented that the third pivotal portion  622  departs from the two fourth pivotal portions  586  along the axial direction of the second pivotal axis  624 . 
     In this embodiment, when the first pivotal axis  604  is pivotally connected to the second pivotal portions  582  of the pivotal member, and the second pivotal axis  624  is pivotally connected to the fourth pivotal portions  586  of the pivotal member, the axial direction of the first pivotal axis  604  is parallel to the axial direction of the second pivotal axis  624 . In this way, the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to present an appearance of being unfolded and folded as a book. 
     Also shown in  FIG. 7 , in this embodiment, the second retaining structure  626  of the second pivotal member  62  is also a slotted hole. The second retaining structure  626  is located on the third pivotal portion  622 . The second protrusion  588  of the pivotal plate  58  is connected to the main body  580 , located between two fourth pivotal portions  586  and extends into the second retaining structure  626 . The second retaining structure  626  has a third retaining edge  626   a  and a fourth retaining edge  626   b  opposite to each other. During rotation of the second riser board  56  relative to the pivotal plate  58  (that is, during rotation of the third pivotal portion  622  and the two fourth pivotal portions  586  relative to the second pivotal axis  624 ), the second protrusion  588  is limitedly moved between the third retaining edge  626   a  and the fourth retaining edge  626   b.    
     Furthermore, the third retaining edge  626   a  of the second retaining structure  626  is adjacent to the end of the third pivotal portion  622  connected to the second fixing portion  620 . The fourth retaining edge  626   b  of the second retaining structure  626  is adjacent to the end of the third pivotal portion  622  away from the second fixing portion  620 . When the second riser board  56  rotates relative to the pivotal plate  58  to make the second protrusion  588  abut against the third retaining edge  626   a , the second riser board  56  is parallel to the pivotal plate  58 . When the second riser board  56  rotates relative to the pivotal plate  58  to make the second protrusion  588  abut against the fourth retaining edge  626   b , the second riser board  56  is perpendicular to the pivotal plate  58 . 
     In view of the above, when the first protrusion  584  abuts against the first retaining edge  606   a  and the second protrusion  588  abuts against the third retaining edge  626   a , the first riser board  54  and the second riser board  56  are parallel to the pivotal plate  58  and present an appearance as an unfolded book. When the first protrusion  584  abuts against the second retaining edge  606   b  and the second protrusion  588  abuts against the fourth retaining edge  626   b , the first riser board  54  and the second riser board  56  are perpendicular to the pivotal plate  58  and present an appearance as a folded book. 
     Additionally, as shown in  FIG. 4 , the first riser board  54  further includes a first control chip  544 . The first control chip  544  of the first riser board  54  is electrically connected to the first memory sockets  540 , so as to control and process the data exchange between the memory modules  64  plugged into the first memory sockets  540  and the motherboard  52 . The second riser board  56  further includes a second control chip  564 . The second control chip  564  of the second riser board  56  is electrically connected to the second memory sockets  560 , so as to control and process the data exchange between the memory modules  64  plugged into the second memory sockets  560  and the motherboard  52 . 
     The first memory sockets  540  on the first riser board  54  are arranged closely. The second memory sockets  560  on the second riser board  56  are arranged closely. Furthermore, when the first riser board  54  and the second riser board  56  are perpendicular to the pivotal plate  58 , the region of the first memory sockets  540  is aligned with the region of the second control chip  564 , while the region of the second memory sockets  564  is aligned with the region of the first control chip  544 . 
     Therefore, through a pivotal structure mutually matched between the first riser board  54  and the pivotal plate  58  and a pivotal structure mutually matched between the second riser board  56  and the pivotal plate  58 , the invention can enable the first riser board  54  and the second riser board  56  to maintain a distance therebetween when being folded to each other, thereby avoiding that the memory modules  64  plugged onto the first riser board  54  come into collision with the second control chip  564  on the second riser board  56 , as well as avoiding that the memory modules  64  plugged onto the second riser board  56  come into collision with the first control chip  544  on the first riser board  54 . 
     However, the shape of the second retaining structure of the invention is not limited to the form of the slotted hole. In another embodiment, the second retaining structure also may be a groove (not shown) formed at the side edge of the third pivotal portion  622 , and the second protrusion  588  is correspondingly configured at the side edge of the fourth pivotal portion  586  and extends into the abovementioned groove, so as to make the second riser board  56  limitedly rotate relative to the pivotal plate  58  as well. 
     As shown in  FIGS. 5A and 5B , in this embodiment, the motherboard  52  of the computer system  5  is configured in the housing  50 . The motherboard  52  at least includes a first riser slot  520  and a second riser slot  522  configured side by side. That is, in this embodiment, the first and second riser slots  520 ,  522  of the motherboard  52  are parallel and adjacent to each other. 
     However, the motherboard  52  may include more than one group of the first riser slot  520  and the second riser slot  522 . In actual applications, the number of groups of the first riser slot  520  and the second riser slot  522  included on the motherboard  52  can be optionally increased or decreased according to actual demands. 
     Additionally, as shown in  FIGS. 4-5B , in this embodiment, the first riser board  54  of the memory combination has a first connection port  542 , and the first connection port  542  is located at a first edge E 1  of the first riser board  54 . The first connection port  542  of the first riser board  54  is used to be plugged into the first riser slot  520  of the motherboard  52 . The second riser board  56  of the memory combination has a second connection port  562 , and the second connection port  562  is located at a second edge E 2  of the second riser board  56 . The second connection port  562  of the second riser board  56  is used to be plugged into the second riser slot  522  of the motherboard  52 . 
     In this embodiment, the first pivotal member  60  is fixed onto the first riser board  54  to be adjacent to the first edge E 1 , and the second pivotal member  62  is fixed onto the second riser board  56  to be adjacent to the second edge E 2 . The first edge E 1  of the first riser board  54  is parallel to the axial direction of the first pivotal axis  604 , and the second edge E 2  of the second riser board  56  is parallel to the axial direction of the second pivotal axis  624 . When the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be parallel to the pivotal plate  58 , the first connection port  542  is just opposite to the second connection port  562 . In other words, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be parallel to the pivotal plate  58 , the pivotal plate  58 , the first connection port  542  and the second connection port  562  are all located between the first riser board  54  and the second riser board  56  (i.e., between the first edge E 1  and the second edge E 2 ). 
     However, the invention is not limited to this. In another embodiment, the first connection port  542  of the first riser board  54  is located at a third edge E 3  of the first riser board  54  to be away from and parallel to the first edge E 1 , while the second connection port  562  of the second riser board  56  is located at a fourth edge E 4  of the second riser board  56  to be away from and parallel to the second edge E 2 . In other words, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , the pivotal plate  58  is located at the same side of the first riser board  54  and the second riser board  56  (i.e., the side of the first edge E 1  and the second edge E 2 ), while the first connection port  542  and the second connection port  562  are located at the other side of the first riser board  54  and the second riser board  56  (i.e., the side of the third edge E 3  and the fourth edge E 4 ). 
     In still another embodiment, the first connection port  542  of the first riser board  54  is located at a fifth edge E 5  of the first riser board  54  to be perpendicular to the first edge E 1 , while the second connection port  562  of the second riser board  56  is located at a sixth edge E 6  of the second riser board  56  to be perpendicular to the second edge E 2  (as the top edges of the first riser board  54  and the second riser board  56  shown in  FIG. 4 ). In other words, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , the pivotal plate  58  is located at the same side of the first riser board  54  and the second riser board  56  (i.e., the side of the first edge E 1  and the second edge E 2 ), while the first connection port  542  and the second connection port  562  are located at the other side of the first riser board  54  and the second riser board  56  (i.e., the side of the fifth edge E 5  and the sixth edge E 6 ). 
     Alternatively, in yet another embodiment, the first connection port  542  of the first riser board  54  is located at a seventh edge E 7  of the first riser board  54  to be perpendicular to the first edge E 1 , while the second connection port  562  of the second riser board  56  is located at a eighth edge E 8  of the second riser board  56  to be perpendicular to the second edge E 2  (as the bottom edges of the first riser board  54  and the second riser board  56  shown in  FIG. 4 ). In other words, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , the pivotal plate  58  is located at the same side of the first riser board  54  and the second riser board  56  (i.e., the side of the first edge E 1  and the second edge E 2 ), and the first connection port  542  and the second connection port  562  are located at the other side of the first riser board  54  and the second riser board  56  (i.e., the side of the seventh edge E 7  and the eighth edge E 8 ). 
     In view of the above, when the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , as long as the first connection port  542  and the second connection port  562  are located at the same side of the first riser board  54  and the second riser board  56 , it can be achieved that the first connection port  542  and the second connection port  562  are respectively plugged into the first riser slot  520  and the second riser slot  522  of the motherboard  52 . 
     In addition, it should be noted that, here, in order to place more memory modules  64  in the limited space of the computer system  5 , in the invention the first memory sockets  540  on the first riser board  54  and the second memory sockets  560  on the second riser board  56  are unaligned with each other. 
     As shown in  FIG. 4 , in this embodiment, the first memory sockets  540  on the first riser board  54  are closely arranged to form a memory socket group, and the second memory sockets  560  on the second riser board  56  are closely arranged to form another memory socket group. In this way, during the process that the first riser board  54  and the second riser board  56  rotate relative to the pivotal plate  58  to be perpendicular to the pivotal plate  58 , the first memory sockets  540  on the first riser board  54  and the second memory sockets  560  on the second riser board  56  are unaligned with each other in an arrangement form of groups, which can effectively utilize the space between the first riser board  54  and the second riser board  56 . 
     From the above detailed description for the specific embodiments of the invention, it can be obviously seen that, an essential feature of the invention is that two boards of the pivotal assembly are pivotally connected with the pivotal plate through two pivotal members, respectively, so that the two boards are capable to be unfolded and folded like a book. Another essential feature of the invention is that each of the two pivotal members, respectively, have a retaining structure for retaining the corresponding protrusion configured on the pivotal plate, so that the two boards are capable to maintain a distance therebetween when being folded, thereby avoiding collision with each other on the two boards. 
     Although the invention has been disclosed with reference to the above embodiments, these embodiments are not intended to limit the invention. Those of skills in the art can make various variations and modifications without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be defined by the appended claims.