Abstract:
An image display system, provided with a plurality of display units and a pointing device for moving a cursor between the plurality of display units, includes a cursor position detecting unit for detecting a desired cursor movement that corresponds to an operation of the pointing device and a cursor movement control unit for moving the cursor commensurate with the operation of the pointing device such that the cursor is moved differently from one display unit to another.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to image display systems and more particularly, to an image display system for displaying images using a plurality of display apparatuses. 
     Recently, users of a personal computer often run a plurality of programs such as a word processor or a spread sheet simultaneously or have a plurality of sets of data displayed on the screen. In such a type of usage, the content to be displayed may be so voluminous that the display area of a single display device proves insufficient. For this reason, systems provided with a plurality of display devices are sometimes used. 
     2. Description of the Related Art 
     Japanese Laid-Open Patent Application No. 62-229325 and Japanese Laid-Open Patent Application No. 62-256125 disclose methods for displaying a cursor in a system provided with a plurality of display device. 
     FIG. 1 shows a coordinate system used in Japanese Laid-Open Patent Application No. 62-229325. As shown in FIG. 1, in Japanese Laid-Open Patent Application No. 62-229325, the position of the pointer is updated within the same coordinate system shared by a CRT  1  and a CRT  2 . 
     FIG. 2 is a flowchart showing an algorithm of a process according to Japanese Laid-Open Patent Application No. 62-229325. 
     As shown in FIG. 2, the pointer position is updated in step S 202  without making any distinction between the CRT  1  and the CRT  2 . 
     FIG. 3 shows a coordinate system used in Japanese Laid-Open Patent Application No. 62-256125. 
     As shown in FIG. 3, in Japanese Laid-Open Patent Application No. 62-256125, the position of a mouse cursor is updated within the same coordinate system (referred to as BMM in Japanese Laid-Open Patent Application No. 62-256125) shared by the CRT  1  and the CRT  2 . 
     FIG. 4 is a flowchart showing an algorithm of a process according to Japanese Laid-Open Patent Application No. 62-256125. 
     As shown in FIG. 4, the cursor coordinate is calculated in step S 2  without making any distinction between the CRTs. 
     The related art disclosed in Japanese Laid-Open Patent Application No. 62-229325 and No. 62-256125 does not assume a case where the number of pixels (pixel count) and a pixel pitch (pixel-to-pixel pitch) differ from one display device (CRT or the like) to another. In other words, the related art does not provide for a process whereby the cursor movement per a mouse input differs from one display device to another in a system where a plurality of display devices characterized by different pixel count and pixel pitch are used. Such an arrangement has a disadvantage in that the cursor cannot be moved smoothly between the plurality of display devices. 
     One type of problem (first problem) related to movement of the cursor is caused by failure to provide a method for updating a cursor display position for each display device. Another type of problem (second problem) is caused by failure to adapt for a cursor movement between different means of display by updating the cursor depending on the display means and the displayed position. 
     A description will now be given of these problems, by contrasting the problems with requirements of users operating a pointing device such as a mouse in a system in which a plurality of display devices are used. 
     The first problems will now be divided into aspects  1 ( a ),  1 ( b ) and  1 ( c ). 
     The aspect  1 ( a ) of the first problem is caused even when the plurality of display devices have identical characteristics (pixel count, pixel pitch etc.) and concerns a user request that the cursor movement be adapted for the displayed content in respective display devices. The aspects  1 ( b ) and  1 ( c ) concern a user request that the cursor be moved in a regular manner from one display device to another even when the display devices have different characteristics. 
     A description will now be given of the details of the individual aspects. 
     According to aspect  1 ( a ), the cursor movement (velocity) cannot be selectively set for individual display devices. In a system using a plurality of display devices, the displayed content may be varied from one display device to another. For example, one display device could be dedicated to display of documents, while another display device could be dedicated to display of diagrams. Finer pointing is required in the display device dedicated to display of diagrams than in the display device dedicated to display of documents. A requirement exists that the mouse cursor be moved slower in the display device dedicated to diagrams than in the display device dedicated to documents in order to enable finer pointing. 
     However, no technology has been available to vary a relationship between an output signal of a pointing device and a distance between cursor display positions before and after the movement (the number of pixels by which the positions are offset from each other). 
     According to aspect  1 ( b ), it is impossible to ensure that, given the same physical movement of the mouse, the distance on one display device between cursor display positions before and after the movement is the same as the corresponding distance on another display device. A requirement exists, particularly in those cases where similar tasks are carried out using a plurality of display devices, that the physical distance that the cursor moves on one display device be the same as the corresponding distance on another display device, given the same mouse movement. According to such a requirement, it is desired that the mouse pointer exhibits a 5 cm on-screen movement both in the display device D 1  and in the display device D 2 , when the mouse is moved 15 cm, for example. 
     FIG. 5 illustrates aspect  1 ( b ) of the related art. Referring to FIG. 5, a display system includes display devices D 31  and D 32 , a computer  21 , a keyboard  22  and a mouse  23 . 
     As indicated by the arrows A 1  and A 2 , a given movement of the mouse  23  do not cause the pointer to move the same on-screen distance on the display device D 31  and on the display device D 32  if the pixel pitches of the display devices D 31  and D 32  are different. 
     According to aspect  1 ( c ), it is impossible to match the rate of a cursor movement on one display device with the corresponding rate on another display device. A requirement exists, when a plurality of display devices are used, that the rate of a mouse cursor movement be the same from one display device to another. For example, assuming that the cursor can be moved end to end on a display device D 1  when the mouse is moved 15 cm, users may desire that the cursor on another display device D 2  be also moved end to end. While aspect  1 ( b ) concerns matching of the distances, aspect  1 ( c ) concerns the rate of the on-screen pointer movement. 
     An operator using a mouse may often have an image of how far the mouse should be moved in order to move the pointer from one end of the screen to another. Such an operator may find a system difficult to use if the pointer moves end to end on one display device and only moves ⅓ of the width of the screen on another display device, when the mouse is moved 15 cm. Stated otherwise, such a user may want the pointer to move at a regular rate on the screen instead of wanting the pointer to move the same distance on different display devices in response to the same mouse operation. 
     FIG. 6 illustrates aspect  1 ( c ) of the related art. In FIG. 6, those components that are the same as the corresponding components in FIG. 5 are designated by the same reference numerals and the description thereof is omitted. 
     Referring to FIG. 6, a display system includes display devices D 41  and D 42  characterized by different pixel counts. The display device D 41  is a 640×480 pixel display and the display device D 42  is a 1600×1200 pixel display. 
     As indicated by the arrows B 1  and B 2 , the same physical movement of the mouse causes the cursor to move end to end in the display device D 41  but causes the cursor to move only a certain distance on the display device D 42 . 
     A description will now be given of the second problem. 
     According to the second problem, the cursor position changes differently depending on its position on the screen. A requirement exists that such a difference be eliminated. 
     More specifically, users having such a requirement and using two display devices arranged horizontally may want the cursor to change its display position in a regular manner when the cursor moves from the top of screen and when it moves from the bottom thereof. 
     FIG. 7 illustrates the second problem of the related art. Referring to FIG. 7 those components that are the same as the corresponding components are designated by the same reference numerals and the description is omitted. 
     As indicated by the broken lines, when the cursor of the mouse  23  is moved from the display device D 41  to the display device D 42  or vice versa, the cursor changes its position differently depending on the position of the cursor on a source screen. More specifically, movement of the cursor between point a and point A occurs in orientations different from the corresponding orientations of the movement between point d and point D. 
     The reason for this irregularity is that, according to the display position calculating method of the related art, the mouse cursor is displayed at the same vertical coordinate before and after the movement from one display device to another. Alternatively, a predetermined value is added to the vertical coordinate on the source display device to determine the vertical coordinate on the destination display device. When the distance between the points a and d on the display device D 41  differs from the distance between the points A and D on the display device D 42 , that difference in the distances is reflected by different vertical positions of the cursor on the display devices D 41  and D 42 . When the number of pixels displayed by the display device D 41  is different from that of the display device D 42 , the cursor moving leftward from point E may not be displayed on the display device D 41  at all. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide an image display system in which the aforementioned problems are eliminated. 
     Another and more specific object of the present invention is to provide an image display system in which a pointer of a pointing device is moved identically on a plurality of display devices characterized by different image displaying capabilities. 
     The aforementioned objects can be achieved by an image display system provided with a plurality of display means and a pointing device for moving a cursor between said plurality of display means, comprising: cursor position detecting means for detecting a cursor movement input that corresponds to an operation of the pointing device; and cursor movement control means for moving the cursor commensurate with the operation of the pointing device such that, given the same cursor movement input detected by said cursor position detecting means, an on-screen movement of the cursor differs from one display means to another. 
     According to the image display system of the present invention, cursor movement and cursor position can be optimized for individual display means. Thus, the cursor can be moved between a plurality of display means in such a way as to best fit the image content displayed on the display means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 shows a coordinate system used in a first image display system of the related art; 
     FIG. 2 is a flowchart showing an algorithm of a process in the first image display system of the related art; 
     FIG. 3 shows a coordinate system used in a second image display system of the related art; 
     FIG. 4 is a flowchart showing an algorithm of a process in the second image display system of the related art; 
     FIG. 5 illustrates a problem in the related art; 
     FIG. 6 illustrates another problem in the related art; 
     FIG. 7 illustrates still another problem in the related art; 
     FIG. 8 illustrates an operating principle of the present invention; 
     FIG. 9 illustrates a schematic construction of an image display system according to a first embodiment of the present invention; 
     FIG. 10 is a block diagram showing a system of the first embodiment; 
     FIG. 11 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of displays according to the first embodiment; 
     FIG. 12 is a flowchart showing a cursor movement process according to the first embodiment; 
     FIG. 13 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of the displays according to a second embodiment; 
     FIG. 14 is a flowchart showing a cursor movement process executed by the CPU  15  according to the second embodiment; 
     FIG. 15 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of the display devices according to a third embodiment; 
     FIG. 16 is a flowchart showing a cursor movement process executed by the CPU according to the third embodiment; 
     FIG. 17 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of the display devices according to a fourth embodiment; 
     FIG. 18 is a flowchart showing a cursor movement process executed by the CPU according to the fourth embodiment; 
     FIG. 19 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of the display devices according to variations of the fourth embodiment; and 
     FIG. 20 shows a schematic construction of a notebook personal computer system to which the embodiments of the present invention could be applied. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 8 illustrates an operating principle of the present invention. 
     An image display system according to the present invention comprises a pointing device  2 , cursor position detecting means  4 , cursor movement controlling means  5  and a plurality of display means  1 - 1 - 1 -n. 
     The pointing device  2  is used to move a cursor  3  between the plurality of display devices  1 - 1 - 1 -n. 
     The cursor movement controlling means  5  moves the cursor  3  responsive to the operation of the pointing device  2 , calling upon different conditions provided for different display means. 
     FIG. 9 illustrates a schematic construction of the image display system according to a first embodiment of the present invention. FIG. 10 is a block diagram showing the system of the first embodiment. 
     The image display system of the first embodiment is a personal computer image display system  11 . 
     Referring to FIG. 9, the personal computer image display system  11  comprises a personal computer  12 , display devices D 1  and D 2  for displaying data processed by the personal computer  12 , a keyboard  13  for inputting data and instructions to the personal computer  12 , a mouse  14  for moving a cursor to images displayed on the display devices D 1  and D 2 . 
     Referring also to FIG. 10, the personal computer  12  comprises a CPU  15  for processing data, a main memory  16  for storing data and programs, a video memory  17  for holding image data of images to be displayed on the display devices D 1  and D 2 , and a bus  18  for connecting the CPU  15 , the main memory  16  and the video memory  17 . The video memory  17  comprises a video memory  17   a  for the display device D 1  and a video memory  17   b  for the display device D 2 . 
     The display device D 1  and the display device D 2  differ from each other in pixel count and pixel pitch, which are inclusively referred to as pixel arrangement in the claims. 
     More specifically, the display device D 1  is capable of displaying 640 pixels in the X direction and 480 pixels in the Y direction. The pixel pitch is set to 0.5 mm. The display device D 2  is capable of displaying 1600 pixels in the X direction and 1280 pixels in the Y direction. The pixel pitch is set to 0.25 mm, that is, about half that of the display device D 1 . The ratio between the pixel count of the display device D 1  and that of the display device D 2  is 2:5. 
     A cursor movement process for moving the cursor between the display devices D 1  and D 2  is executed by the CPU  15  according to a program stored in the main memory  16 . 
     The first embodiment uses a virtual mouse cursor coordinate system Cp which is separate from actual display coordinate systems of the display devices D 1  and D 2 . The virtual coordinate system Cp is related to the display coordinate system C 1  of the display device D 1  and the display coordinate system C 2  of the display device D 2  in the following manner. 
     
       
           x 1= xp/ 2  (1) 
       
     
     
       
           y 1= yp/ 2  (2) 
       
     
     
       
           x 2= xp− 1280  (3) 
       
     
     
       
           y 2= yp   (4) 
       
     
     The range of the coordinate system Cp is defined as follows. 
     
       
         0≦ xp≦ 640, 0≦ yp&lt; 480  (5) 
       
     
     
       
         640≦ xp≦ 1440, 0≦ yp≦ 640  (6) 
       
     
     FIG. 11 illustrates the relationship between the virtual coordinate system of the cursor and the coordinate systems of the displays according to the first embodiment. FIG. 11 is a graphical representation of the numeral relations of (1)-(6). 
     Referring to FIG. 11, X coordinates in the virtual coordinate system Cp are marked above the X axis and Y coordinates in the coordinate system Cp are marked to the left of the Y axis. X coordinates in the coordinate system C 1  of the display device D 1  and the coordinate system C 2  of the display device D 2  are marked below the X axis. Y coordinates in the coordinate systems C 1  and C 2  are marked to the right of the Y axis. 
     The virtual coordinate system Cp is configured for a pixel pitch of 0.25 mm. Since 1 pixel in the coordinate system C 1  of the display device D 1  having a pixel pitch of 0.5 mm corresponds to 2 pixels in the virtual coordinate system Cp, a given point may have a Y coordinate “400” in the virtual coordinate system Cp and “200” in the coordinate system C 1 . Another point may have a Y coordinate “800” in the virtual coordinate system Cp and “400” in the coordinate system C 1 . 
     Since 1 pixel in the coordinate system C 2  of the display device D 2  having a pixel pitch of 0.25 mm corresponds to 1 pixel in the virtual coordinate system Cp, a given point may have a Y coordinate “400” in the virtual coordinate system Cp and “400” in the coordinate system C 1 . Another point may have a Y coordinate “800” in the virtual coordinate system Cp and “800” in the coordinate system C 1 . 
     FIG. 12 is a flowchart showing a cursor movement process executed by the CPU  15  according to the first embodiment. 
     When the mouse  14  is operated, the CPU  15  is supplied, from the mouse  14 , with information P(px, py) indicating the movement of a cursor. The CPU  15  then adds the information P(px, py) indicating the movement of the cursor to the current coordinates Cp(xp, yp) of the cursor in the virtual coordinate system Cp (steps S 1 - 1 , S 1 - 2 ). 
     When the information P(px, py) indicating the movement of the cursor is added to the current cursor coordinates Cp(xp, yp) in the virtual coordinate system Cp in step S 1 - 2 , the cursor position in the virtual coordinate system Cp is updated. 
     The CPU  15  then modifies the cursor coordinates Cp(px, py) updated in step S 1 - 2  so that the cursor coordinates Cp(px, py) are located in a displayable area (step S 1 - 3 ). 
     More specifically, in step S 1 - 3 , if the X coordinate xp of the cursor coordinates Cp(px, py) updated in step S 1 - 2  is smaller than 0, that is, if the X coordinate xp is smaller than the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 , the X coordinate xp is located inside a displayable area of the display device D 1  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 , that is, by setting the X coordinate xp to 0. If the Y coordinate yp is smaller than 0, that is, if the Y coordinate yp is smaller than the Y coordinate of the vertical edge of the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , respectively, the Y coordinate yp is located inside the displayable area of the display devices D 1  and D 2  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , respectively, that is, by setting the Y coordinate yp to 0. 
     If the X coordinate xp is greater than 2879, that is, if the X coordinate is greater than the X coordinate of the horizontal edge of the coordinate system C 2  of the display device D 2 , the X coordinate xp is located inside the displayable area of the display device D 2  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system of the display device D 2 , that is, by setting the X coordinate to 2879. 
     If the X coordinate xp is smaller than 1280 and the Y coordinate yp is greater than 959, that is, greater than the Y coordinate yp of the vertical edge of the coordinate system C 1  of the display device D 1 , the Y coordinate yp is located inside the displayable area of the display device D 1  by setting the Y coordinate yp to the Y coordinate yp of the vertical edge of the coordinate system C 1  of the display device D 1 , that is, by setting the Y coordinate yp to 959. 
     If the Y coordinate yp is greater than 1279, that is, greater than the Y coordinate of the vertical edge of the coordinate system C 2  of the display device D 2 , the Y coordinate yp is located inside the displayable area of the display device D 2  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate system C 2  of the display device D 2 , that is, by setting the Y coordinate yp to 1279. 
     With the above-described arrangement, the virtual cursor coordinates Cp(xp, yp) are located in the coordinate systems C 1  and C 2 , that is, in the displayable area of the display devices D 1  and D 2 . 
     Having located the virtual coordinates Cp(xp, yp) in the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , respectively, the CPU  15  then determines whether the cursor is located in the displayable area of the display device D 1  or the displayable area of the display device D 2  (step S 1 - 4 ). 
     More specifically, in step S 1 - 4 , the X coordinate xp of the virtual cursor coordinates Cp(xp, yp) is referred to for the determination. If the X coordinate xp is smaller than 1280, it is determined that the cursor is located in the displayable area of the display device D 1 . If the X coordinate xp is equal to or greater than 1280, it is determined that the cursor is located in the displayable area of the display device D 2 . 
     If it is determined in step S 1 - 4  that the cursor is located in the displayable area of the display device D 1 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to coordinates C 1 (x1, y1) of the display device D 1  and stores image data of the cursor in the video memory  17   a  for the display device D 1  at addresses corresponding to the coordinates C 1 (x1, y1) (step S 1 - 5 ). 
     More specifically, in step S 1 - 5 , the CPU  15  sets the X coordinate x1 of the coordinates C 1 (x1, y1) to xp/2. The CPU  15  also sets the Y coordinate y1 of the coordinates C 1 (x1, y1) to yp/2. 
     If it is determined in step S 1 - 4  that the cursor is located in the displayable area of the display device D 2 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 2 (x2, y2) of the display device D 2  and stores image data of the cursor in the video memory  17   b  for the display device D 2  at addresses corresponding to the coordinates C 2 (x2, y2) (step S 1 - 6 ). 
     More specifically, in step S 1 - 6 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 2 (x2, y2) of the display device D 2  by subtracting 1280 (the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 ) from the X coordinate xp of the virtual cursor coordinates Cp(xp, yp). Since the pixel pitch of the display device D 2  is the same as that of the virtual coordinate system, the Y coordinate y2 of the coordinates C 2 (x2, y2) of the display device D 2  is set to the Y coordinate yp. 
     With the above-described arrangement, the ratio between the movement of the cursor on the display device D 1  and the movement on the display device D 2  is 1:2. Since the ratio between the pixel pitch on the display device D 1  and the pixel pitch on the display device D 2  is 2:1, the cursor display position moves regularly across the display devices D 1  and D 2 . 
     Thus, according to the first embodiment, regular movement of the cursor across the display devices D 1  and D 2  is ensured notwithstanding the difference otherwise found between the mouse-driven cursor movement on the display device D 1  and the corresponding movement on the display device D 2 . In this way, the problem relating to aspect  1 ( c ) of the related art is resolved. 
     There are other approaches for determining and converting the cursor movement. For example, when the mouse cursor is displayed on the display device D 1 , outputs from the mouse could be processed in steps of 2, and, when the mouse cursor is displayed on the display device D 2 , outputs from the mouse could be processed in steps of 1. 
     According to this variation of the first embodiment, when the mouse cursor display position moves from the display device D 1  to the display device D 2 , y1 is added to the Y coordinate y1 of the coordinates C 1 (x1, y1) of the display device D 1  (i.e. y1 is doubled) so as to obtain the Y coordinate y2 of the coordinates C 2 (x2, y2) of the display device D 2 . 
     When the mouse cursor display position moves from the display device D 2  to the display device D 1 , −y2/2 is added to the Y coordinate y2 of the coordinates C 2 (x2, y2) of the display device D 2  (i.e. y2 is divided by 2) so as to obtain the Y coordinate y1 of the coordinates C 1 (x1, y1) of the display device D 1 . In this way, the problem relating to aspect  1 ( c ) is resolved. 
     The first embodiment and its variation described are directed to the display position of the mouse cursor. However, the present invention is also applicable to calculating the display position of painting software objects and the like moved on the screen by mouse operation. Although the above description gives an example of two display means connected to each other, the first embodiment and its variation can easily be applied to three or more display means connected to each other. 
     Further, the above description assumes that a predetermined mathematical relation is used to update the display position. However, the method of calculating the display position may be determined by the user for each display device. 
     The variation of the first embodiment may be modified such that the user specifies the step count for each display means so that the step count is referred to when the display position is updated. 
     Alternatively, several predetermined speed patterns for displaying the cursor may be provided as options. For example, a high-speed pattern and a low-speed pattern could be provided for the user to choose from. The display position may be updated such that outputs from the mouse are processed in steps of 1 in accordance with the high-speed pattern and in step of 2 in accordance with the low-speed pattern. 
     The ratio between the pixel count of the display device D 1  and that of the display device D 2  is 2:5. Thus, with the related art discussed with reference to FIG. 5, a manual mouse movement that causes the cursor to move from end to end on the display device D 1  can only move the cursor 40% of the same distance on the display device D 2 . 
     According to the first embodiment and its variation, however, the cursor movement rate is double that of the display device D 1  available on the display device D 2 . Therefore, the problem relating to aspect  1 ( b ) explained with reference to FIG. 5 is resolved to a great extent. 
     It is to be noted that the first embodiment and its variation ensure that a positive value of Y coordinate is added to the source Y coordinate when the cursor display position is moved from the display device D 1  to the display device D 2 , and a negative value of Y coordinate is added to the source Y coordinate when the cursor display position is moved from the display device D 2  to the display device D 1 . 
     For example, when the cursor at the source Y coordinate y1=10 of the display device D 1  is moved to the display device D 2 , 10 is added to the source Y coordinate y1. When the source Y coordinate y1 is 200, 200 is added to the source Y coordinate y1. Thus, the value added to the source Y coordinate y1 varies depending on the value of the source Y coordinate y1. The greater the value of the source Y coordinate y1, the larger the value added to the source Y coordinate y1, resulting in smooth movement of the cursor from the display device D 1  to the display device D 2 . 
     When the cursor at the source Y coordinate y2=20 of the display device D 2  is moved to the display device D 1 , −10 is added to the source Y coordinate y2. When the source Y coordinate y2 is 400, −200 is added to the source Y coordinate y2. Thus, the value added to the source Y coordinate y2 varies depending on the value of the source Y coordinate y2. The greater the value of the source Y coordinate y2, the smaller the value added to the source Y coordinate y2, resulting in smooth movement of the cursor from the display device D 2  to the display device D 1 . 
     The added value may not necessarily vary in strict accordance with the source Y coordinate. For example, the same value 200 may be added to the source Y coordinate y1=399 and the source Y coordinate y1=400. Accordingly, the second problem described with reference to FIG. 7 (difference in orientation of movement between movement a−A and movement A−D) is resolved. Moreover, according to the first embodiment and its variation, most of the points on the display device D 2  will find corresponding points on the display device D 1 . Very few points on the display device D 2  will be like point E as shown in FIG.  7 . 
     A description will now be given of a second embodiment of the present invention. FIG. 13 illustrates the relationship between the virtual coordinate system of the cursor and coordinate systems C 11  and C 12  of display devices D 11  and D 12 , respectively, according to the second embodiment. The ratio between the pixel count of the display device D 11  and that of the display device D 12  is 2:5. It is to be noted that vertical coordinates of the display device D 11  are defined in terms of a distance from the bottom. The other aspects of the construction of a computer system assumed in the second embodiment is the same as that of the first embodiment, and the description thereof is omitted. 
     The virtual coordinate system Cp shown in FIG. 13 is related to the coordinate system C 11  of the display device D 11  and the coordinate system C 12  of the display device D 12  in the following manner. 
     
       
           x 11= xp/ 2  (7) 
       
     
     
       
           y 11=480−( yp/ 2)  (8) 
       
     
     
       
           x 12= xp− 1280  (9) 
       
     
     
       
           y 12= yp   (10) 
       
     
     FIG. 14 is a flowchart showing a cursor movement process executed by the CPU  15  according to the second embodiment. 
     When the mouse  14  is operated, the CPU  15  is supplied with information P(px, py) from the mouse  14  indicating the movement of a cursor. The CPU  15  then adds the information P(px, py) indicating the movement of the cursor to the current coordinates Cp(xp, yp) of the cursor in the virtual coordinate system Cp (steps S 2 - 1 , S 2 - 2 ). 
     When the information P(px, py) indicating the movement of the cursor is added to the current cursor coordinates Cp(xp, yp) in the virtual coordinate system Cp in step S 2 - 2 , the cursor position in the virtual coordinate system Cp is updated. 
     The CPU  15  then modifies the cursor coordinates Cp(px, py) updated in step S 2 - 2  so that the cursor coordinates Cp(px, py) are located in a displayable area (step S 2 - 3 ). 
     More specifically, in step S 2 - 3 , if the X coordinate xp of the cursor coordinates Cp(px, py) updated in step S 2 - 2  is smaller than 0, that is, if the X coordinate xp is smaller than the X coordinate of the horizontal edge of the coordinate system C 11  of the display device D 11 , the X coordinate xp is located inside a displayable area of the display device D 11  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system C 11  of the display device D 11 , that is, by setting the X coordinate xp to 0. If the Y coordinate yp is smaller than 0, that is, if the Y coordinate yp is smaller than the Y coordinate of the vertical edge of the coordinate systems C 11  and C 12  of the display devices D 11  and D 12 , respectively, the Y coordinate yp is located inside the displayable area of the display devices D 11  and D 12  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate systems C 11  and C 12  of the display devices D 11  and D 12 , respectively, that is, by setting the Y coordinate yp to 0. 
     If the X coordinate xp is greater than 2879, that is, if the X coordinate is greater than the X coordinate of the horizontal edge of the coordinate system C 12  of the display device D 12 , the X coordinate xp is located inside the displayable area of the display device D 12  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system of the display device D 12 , that is, by setting the X coordinate to 2879. 
     If the X coordinate xp is smaller than 1280 and the Y coordinate yp is greater than 959, that is, greater than the Y coordinate yp of the vertical edge of the coordinate system C 11  of the display device D 11 , the Y coordinate yp is located inside the displayable area of the display device D 11  by setting the Y coordinate yp to the Y coordinate yp of the vertical edge of the coordinate system C 11  of the display device D 11 , that is, by setting the Y coordinate yp to 959. 
     If the Y coordinate yp is greater than 1279, that is, greater than the Y coordinate of the vertical edge of the coordinate system C 12  of the display device D 12 , the Y coordinate yp is located inside the displayable area of the display device D 12  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate system C 12  of the display device D 12 , that is, by setting the Y coordinate yp to 1279. 
     With the above-described arrangement, the virtual cursor coordinates Cp(xp, yp) are located in the coordinate systems C 11  and C 12 , that is, in the displayable area of the display devices D 11  and D 12 . 
     Having located the virtual coordinates Cp(xp, yp) in the coordinate systems C 11  and C 12  of the display devices D 11  and D 12 , respectively, the CPU  15  then determines whether the cursor is located in the displayable area of the display device D 11  or the displayable area of the display device D 12  (step S 2 - 4 ). 
     More specifically, in step S 2 - 4 , the X coordinate xp of the virtual cursor coordinates Cp(xp, yp) is referred to for the determination. If the X coordinate xp is smaller than 1280, it is determined that the cursor is located in the displayable area of the display device D 11 . If the X coordinate xp is equal to or greater than 1280, it is determined that the cursor is located in the displayable area of the display device D 12 . 
     If it is determined in step S 2 - 4  that the cursor is located in the displayable area of the display device D 11 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to coordinates C 11 (x11, y11) of the display device D 11  and stores image data of the cursor in the video memory  17   a  for the display device D 11  at addresses corresponding to the coordinates C 11 (x11, y11) (step S 2 - 5 ). 
     More specifically, in step S 2 - 5 , the CPU  15  sets the X coordinate x11 of the coordinates C 11 (x11, y11) to xp/2. The CPU  15  also sets the Y coordinate y11 of the coordinates C 11 (x11, y11) to 480−−yp/2. 
     If it is determined in step S 2 - 4  that the cursor is located in the displayable area of the display device D 12 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 12 (x12, y12) of the display device D 12  and stores image data of the cursor in the video memory  17   b  for the display device D 12  at addresses corresponding to the coordinates C 12 (x12, y12) (step S 2 - 6 ). 
     More specifically, in step S 2 - 6 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 12 (x12, y12) of the display device D 12  by subtracting 1280 (the X coordinate of the horizontal edge of the coordinate system C 11  of the display device D 11 ) from the X coordinate xp of the virtual cursor coordinates Cp(xp, yp). Since the pixel pitch of the display device D 12  is the same as that of the virtual coordinate system, the Y coordinate y12 of the coordinates C 12 (x12, y12) of the display device D 12  is set to the Y coordinate yp. 
     The second embodiment leaves the problem described with reference to FIG. 7 unsolved. In order to eliminate points like point E that have no corresponding points on the other display, the relationship between the virtual coordinate system and the coordinate system of the displays may be modified. 
     A description will now be given of a third embodiment. FIG. 15 illustrates the relationship between the virtual coordinate system of the cursor and coordinate systems C 21  and C 22  of display devices D 21  and D 22 , respectively, according to the third embodiment. The construction of a computer system assumed in the third embodiment is the same as that of the first embodiment, and the description thereof is omitted. 
     The virtual coordinate system Cp shown in FIG. 15 is related to the coordinate system C 21  of the display device D 21  and the coordinate system C 22  of the display device D 22  in the following manner. 
     
       
           x 21= xp/ 5  (13) 
       
     
     
       
           y 21= yp/ 5  (14) 
       
     
     
       
           x 22=( xp− 3280)/2  (15) 
       
     
     
       
           y 22= yp/ 2  (16) 
       
     
     FIG. 16 is a flowchart showing a cursor movement process executed by the CPU  15  according to the third embodiment. 
     When the mouse  14  is operated, the CPU  15  is supplied with information P(px, py) from the mouse  14  indicating the movement of a cursor. The CPU  15  then adds the information P(px, py) indicating the movement of the cursor to the current coordinates Cp(xp, yp) of the cursor in the virtual coordinate system Cp (steps S 3 - 1 , S 3 - 2 ). 
     When the information P(px, py) indicating the movement of the cursor is added to the current cursor coordinates Cp(xp, yp) in the virtual coordinate system Cp in step S 3 - 2 , the cursor position in the virtual coordinate system Cp is updated. 
     The CPU  15  then modifies the cursor coordinates Cp(px, py) updated in step S 3 - 2  so that the cursor coordinates Cp(px, py) are located in a displayable area (step S 3 - 3 ). 
     More specifically, in step S 3 - 3 , if the X coordinate xp of the cursor coordinates Cp(px, py) updated in step S 3 - 2  is smaller than 0, that is, if the X coordinate xp is smaller than the X coordinate of the horizontal edge of the coordinate system C 21  of the display device D 21 , the X coordinate xp is located inside a displayable area of the display device D 21  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system C 21  of the display device D 21 , that is, by setting the X coordinate xp to 0. If the Y coordinate yp is smaller than 0, that is, if the Y coordinate yp is smaller than the Y coordinate of the vertical edge of the coordinate systems C 21  and C 22  of the display devices D 21  and D 22 , respectively, the Y coordinate yp is located inside the displayable area of the display devices D 21  and D 22  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate systems C 21  and C 22  of the display devices D 21  and D 22 , respectively, that is, by setting the Y coordinate yp to 0. 
     If the X coordinate xp is greater than 6399, that is, if the X coordinate is greater than the X coordinate of the horizontal edge of the coordinate system C 22  of the display device D 22 , the X coordinate xp is located inside the displayable area of the display device D 22  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system of the display device D 22 , that is, by setting the X coordinate to 6399. 
     If the Y coordinate yp is greater than 2399, that is, greater than the Y coordinate of the vertical edge of the coordinate system C 21  of the display device D 21  and the coordinate system C 22  of the display device D 22 , the Y coordinate yp is located inside the displayable area of the display devices D 21  and D 22  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate system C 21  of the display device D 21  and the coordinate system C 22  of the display device D 22 , that is, by setting the Y coordinate yp to 2399. 
     With the above-described arrangement, the virtual cursor coordinates Cp(xp, yp) are located in the coordinate systems C 21  and C 22 , that is, in the displayable area of the display devices D 21  and D 22 . 
     Having located the virtual coordinates Cp(xp, yp) in the coordinate systems C 21  and C 22  of the display devices D 21  and D 22 , respectively, the CPU  15  then determines whether the cursor is located in the displayable area of the display device D 21  or the displayable area of the display device D 22  (step S 3 - 4 ). 
     More specifically, in step S 3 - 4 , the X coordinate xp of the virtual cursor coordinates Cp(xp, yp) is referred to for the determination. If the X coordinate xp is smaller than 3200, it is determined that the cursor is located in the displayable area of the display device D 21 . If the X coordinate xp is equal to or greater than 3200, it is determined that the cursor is located in the displayable area of the display device D 22 . 
     If it is determined in step S 3 - 4  that the cursor is located in the displayable area of the display device D 21 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to coordinates C 21 (x21, y21) of the display device D 21  and stores image data of the cursor in the video memory  17   a  for the display device D 21  at addresses corresponding to the coordinates C 21 (x21, y21) (step S 3 - 5 ). 
     More specifically, in step S 3 - 5 , the CPU  15  sets the X coordinate x21 of the coordinates C 21 (x21, y21) to xp/5. The CPU  15  also sets the Y coordinate y21 of the coordinates C 21 (x21, y21) to 480−yp/2. 
     If it is determined in step S 3 - 4  that the cursor is located in the displayable area of the display device D 22 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 22 (x22, y22) of the display device D 22  and stores image data of the cursor in the video memory  17   b  for the display device D 22  at addresses corresponding to the coordinates C 22 (x22, y22) (step S 3 - 6 ). 
     More specifically, in step S 3 - 6 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 22 (x22, y22) of the display device D 22  by subtracting 3200 (the X coordinate of the horizontal edge of the coordinate system C 22  of the display device D 22 ) from the X coordinate xp of the virtual cursor coordinates Cp(xp, yp) and then dividing the result by 2, and by dividing the Y coordinates yp by 2. 
     With the above arrangement, movement across 5 pixels in the virtual coordinate system corresponds to movement across 1 pixel in the coordinate system C 21  of the display device D 21 . Movement across 2 pixels in the virtual coordinate system corresponds to movement across 1 pixel in the coordinate system C 22  of the display device D 22 . Therefore, movement across 5 pixels on the display device D 21  corresponds to movement across 2 pixels on the display device D 22 . Since the ratio between the pixel count of the display device D 21  and that of the display device D 22  is 2:5, the cursor movement can be processed in an identical manner in the display device D 21  and in the display device D 22 . 
     While it is assumed in the above description that the mouse cursor is displayed on one display means at a time, portions of the coordinate system C 21  and the coordinate system C 22  may be overlapped so that the mouse cursor is displayed on two display means at the same time. 
     A description will now be given of a fourth embodiment of the present invention. FIG. 17 illustrates the relationship between the virtual coordinate system of the cursor and coordinate systems C 1  and C 2  of display devices D 1  and D 2 , respectively, according to the fourth embodiment. FIG. 18 is a flowchart showing a cursor movement process executed by the CPU  15  according to the fourth embodiment. The construction of a computer system assumed in the fourth embodiment is the same as that of the first embodiment, and the description thereof is omitted. 
     In the fourth embodiment, the coordinate system C 1  of the display device D 1  and the coordinate system C 2  of the display device D 2  are made to overlap each other in a hatched overlapping area C 1 - 2 . The cursor at the coordinates located in the overlapping area is displayed both on the display device D 1  and the display device D 2 . 
     When the mouse  14  is operated, the CPU  15  is supplied with information P(px, py) from the mouse  14  indicating the movement of a cursor. The CPU  15  then adds the information P(px, py) indicating the movement of the cursor to the current coordinates Cp(xp, yp) of the cursor in the virtual coordinate system Cp (steps S 4 - 1 , S 4 - 2 ). 
     When the information P(px, py) indicating the movement of the cursor is added to the current cursor coordinates Cp(xp, yp) in the virtual coordinate system Cp in step S 4 - 2 , the cursor position in the virtual coordinate system Cp is updated. 
     The CPU  15  then modifies the cursor coordinates Cp(px, py) updated in step S 4 - 2  so that the cursor coordinates Cp(px, py) are located in a displayable area (step S 4 - 3 ). 
     More specifically, in step S 4 - 3 , if the X coordinate xp of the cursor coordinates Cp(px, py) updated in step S 4 - 2  is smaller than 0, that is, if the X coordinate xp is smaller than the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 , the X coordinate xp is located inside a displayable area of the display device D 1  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 , that is, by setting the X coordinate xp to 0. If the Y coordinate yp is smaller than 0, that is, if the Y coordinate yp is smaller than the Y coordinate of the vertical edge of the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , the Y coordinate yp is located inside the displayable area of the display devices D 1  and D 2  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , that is, by setting the Y coordinate yp to 0. 
     If the X coordinate xp is greater than 2779, that is, if the X coordinate is greater than the X coordinate of the horizontal edge of the coordinate system C 2  of the display device D 2 , the X coordinate xp is located inside the displayable area of the display device D 2  by setting the X coordinate xp to the X coordinate of the horizontal edge of the coordinate system of the display device D 2 , that is, by setting the X coordinate to 2779. 
     If the X coordinate xp is smaller than 1180 and the Y coordinate yp is greater than 959, that is, greater than the Y coordinate yp of the vertical edge of the coordinate system C 1  of the display device D 1 , the Y coordinate yp is located inside the displayable area of the display device D 1  by setting the Y coordinate yp to the Y coordinate yp of the vertical edge of the coordinate system C 1  of the display device D 1 , that is, by setting the Y coordinate yp to 959. 
     If the Y coordinate yp is greater than 1179, that is, greater than the Y coordinate of the vertical edge of the coordinate system C 2  of the display device D 2 , the Y coordinate yp is located inside the displayable area of the display device D 2  by setting the Y coordinate yp to the Y coordinate of the vertical edge of the coordinate system C 2  of the display device D 2 , that is, by setting the Y coordinate yp to 1179. 
     With the above-described arrangement, the virtual cursor coordinates Cp(xp, yp) are located in the coordinate systems C 1  and C 2 , that is, in the displayable area of the display devices D 1  and D 2 . 
     Having located the virtual coordinates Cp(xp, yp) in the coordinate systems C 1  and C 2  of the display devices D 1  and D 2 , respectively, the CPU  15  then determines whether the cursor is located in the displayable area of the display device D 1  or the displayable area of the display device D 2  (steps S 4 - 4 , S 4 - 6 ). 
     More specifically, in steps S 4 - 4  and S 4 - 6 , the X coordinate xp of the virtual cursor coordinates Cp(xp, yp) is referred to for the determination. If it is found in step S 4 - 4  that the X coordinate xp is smaller than 1280, it is determined that the cursor is displayed only on the display device D 1  or is displayed in the overlapping area C 1 - 2 . If the X coordinate xp is equal to or greater than 1280, it is determined that the cursor is displayed only on the display device D 2 . If it is found in step S 4 - 6  that the X coordinate xp is smaller than 1180, it is determined that the cursor is displayed only on the display device D 1 . 
     If it is determined in steps S 4 - 4  and S 4 - 6  that the cursor is displayed only on the display device D 1 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to coordinates C 1 (x1, y1) of the display device D 1  and stores image data of the cursor in the video memory  17   a  for the display device D 1  at addresses corresponding to the coordinates C 1 (x1, y1) (step S 4 - 5 ). 
     More specifically, in step S 4 - 5 , the CPU  15  sets the X coordinate x1 of the coordinates C 1 (x1, y1) to xp/2. The CPU  15  also sets the Y coordinate y1 of the coordinates C 1 (x1, y1) to yp/2. 
     If it is determined in step S 4 - 4  that the cursor is displayed only on the display device D 2 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 2 (x2, y2) of the display device D 2  and stores image data of the cursor in the video memory  17   b  for the display device D 2  at addresses corresponding to the coordinates C 2 (x2, y2) (step S 4 - 7 ). 
     More specifically, in step S 4 - 7 , the CPU  15  converts the virtual cursor coordinates Cp(xp, yp) to the coordinates C 2 (x2, y2) of the display device D 2  by subtracting 1180 (the X coordinate of the horizontal edge of the coordinate system C 1  of the display device D 1 ) from the X coordinate xp of the virtual cursor coordinates Cp(xp, yp). Since the pixel pitch of the display device D 2  is the same as that of the virtual coordinate system, the Y coordinate y2 of the coordinates C 2 (x2, y2) of the display device D 2  is set to the Y coordinate yp. 
     If it is found in step S 4 - 6  that the X coordinate xp is equal to or greater than 1180, it is determined that the cursor is located in the overlapping area C 1 - 2  where the displayable area of the display device D 1  and the displayable area of the display device D 2  overlap each other, both the steps S 4 - 5  and S 4 - 7  are executed so that the cursor is displayed on both the display device D 1  and the display device D 2 . 
     With the above arrangement, the cursor at the coordinates located in the overlapping area C 1 - 2  is displayed both on the display device D 1  and the display device D 2 . Therefore, it is easy to keep track of the cursor position and the operability is improved. 
     Briefly reviewing, the present invention resolves or relieves the following problems inherent to the related art: 
     1) Inability to change the rate of movement of the cursor depending on the display means. 
     2) Inability to match the on-screen distance of cursor movement on one display means with that of another display means in response to a given physical movement of a mouse. 
     3) Inability to match the on-screen rate of cursor movement on one display means with that of another display means in response to a given physical movement of a mouse. 
     4) Unnatural movement of the cursor between the display means. 
     A description will now be given of variations of the fourth embodiment. 
     In a first variation, the coordinate system C 1  of the display device D 1  having a pixel count of B 1  and the coordinate system C 2  of the display device D 2  having a pixel count of B 2  larger than the pixel count B 1  are connected to each other such that the coordinate axes are aligned with each other. A cursor position calculation is introduced such that the greater the values of the cursor coordinates on the display device D 2 , the smaller the amount of movement of the cursor on the display device D 2  in response to a unit mouse movement. In this way, smooth cursor movement in the overlapping area is ensured. 
     In a second variation, the coordinate system C 1  of the display device D 1  having a pixel count of B 1  and the coordinate system C 2  of the display device D 2  having a pixel count of B 2  larger than the pixel count B 1  are connected to each other such that the coordinate axes are 180° horizontally offset from each other (see FIG.  19 ). A cursor position calculation is introduced such that the greater the values of the cursor coordinates on the display device D 2 , the greater the amount of movement of the cursor on the display device D 2  in response to a unit mouse movement. The second variation also ensures smooth cursor movement in the overlapping area. 
     While the first and second variations ensure smooth movement of the cursor by controlling the cursor movement depending on the pixel count of a display device. The cursor movement may be controlled depending on the pixel pitch. 
     For example, a third variation of the fourth embodiment may be such that the coordinate system C 51  of the display device D 51  having a pixel pitch of S 1  and the coordinate system C 52  of the display device D 52  having a pixel pitch of S 2  greater than the pixel pitch S 1  are connected to each other such that the coordinate axes are aligned. A cursor position calculation is introduced such that the greater the values of the cursor coordinates on the display device D 51 , the smaller the amount of movement of the cursor on the display device D 1  in response to a unit mouse movement. As a result, the cursor movement per a unit mouse movement becomes small as the cursor approaches the display device D 52  so as to become more like the movement on the display device D 52  in the overlapping area. In this way, smooth cursor movement between the display device D 51  and the display device D 52  is ensured. 
     A fourth variation of the fourth embodiment will be described. The coordinate system C 51  of the display device D 51  having a pixel pitch of S 1  and the coordinate system C 52  of the display device D 52  having a pixel pitch of S 2  greater than the pixel pitch S 1  are connected to each other such that the coordinate axes are 180° horizontally rotated from each other (see FIG.  19 ). A cursor portion calculation is introduced such that the greater the values of the cursor coordinates on the display device D 51 , the greater the amount of movement of the cursor on the display device D 1  in response to a unit mouse movement. As a result, the cursor movement per a unit mouse movement becomes great as the cursor moves away from the display device D 52  so as to become more like the movement on the display device D 52  in the overlapping area. In this way, smooth cursor movement between the display device D 51  and the display device D 52  is ensured. Since the cursor at a position on the display device D 1  away from the display device D 2  is moved at a rate adapted for the pixel count of the display device D 1 , the cursor can be moved efficiently on the display device D 1 . 
     It is to be noted that the first through fourth embodiments of the present invention could equally be applied to a desktop personal computer system and a notebook personal computer system characterized by a small displayable area. 
     FIG. 20 shows a schematic construction of a notebook personal computer system to which the embodiments of the present invention could be applied. Referring to FIG. 20, a notebook personal computer system comprises a notebook personal computer  18 , an auxiliary display  19  and an interface cable  20 . 
     The notebook personal computer  18  is provided with a display  18   a , a keyboard  11   b  and a pointing device  11   c . The auxiliary display  19 , connected to the notebook personal computer via a digital interface, is designed to display a work area different from the area displayed by the display  18   a.    
     When a cursor movement is prescribed by the pointing device  11   c , one of the cursor movement processes described with reference to FIGS. 11 through 16 is employed depending on the pixel count of the display  18   a  and the auxiliary display  19 . Thus, smooth cursor movement between the display  18   a  and the auxiliary display  19  is ensured allowing efficient operation on the notebook personal computer system. 
     The present invention is not limited to the above described embodiments, and variations and modifications may be made without departing from the scope of the present invention.