Patent Publication Number: US-7908517-B2

Title: Information processing apparatus with resume function and information processing system

Description:
CROSSED-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of application Ser. No. 12/076,799, filed Mar. 24, 2008, now U.S. Pat. No. 7,661,029; which is a continuation of application Ser. No. 10/659,292, filed Sep. 11, 2003, now U.S. Pat. No. 7,366,950; which is a continuation of application Ser. No. 10/285,447, filed Nov. 1, 2002, now U.S. Pat. No. 6,662,311; which is a continuation of application Ser. No. 09/407,840, filed Sep. 29, 1999, now U.S. Pat. No. 6,502,207; which is a continuation of application Ser. No. 08/975,054, filed Nov. 20, 1997, now U.S. Pat. No. 5,968,186; which is a continuation of application Ser. No. 08/667,583, filed Jun. 24, 1996, now U.S. Pat. No. 5,721,932; which is a continuation of application Ser. No. 08/001,248, filed Jan. 6, 1993, now U.S. Pat. No. 5,592,675, the contents of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an information processing apparatus such as a personal computer, and more particularly, to a resume function for reproducing the work state that existed when a power source of the processing apparatus was turned off, upon turning on the power source again. The present invention also relates to a resume function in an information processing system which has a plurality of information processing apparatuses connected through a network. 
     Thanks to the advance of small device mounting techniques and development of power consumption reducing techniques in recent years, personal computers, work stations, word processors and so on (hereinafter they are called “information processing apparatuses”) have become increasingly smaller in size, and even notepad size products operable with a battery have recently been brought to the market. Such battery driven information processing apparatuses require a user to frequently shut off the power supply either manually or automatically in order to prevent the battery from being consumed in a short time. However, when the power source is to be turned off, the user is required to store user information, for example, a document under processing and so on, in a non-volatile storage unit, and moreover, when the power source is to be turned on again, the user must recall a program and the thus stored user information from the non-volatile storage unit. For this reason, such frequent turning-off of the power source causes a problem that efficient use of the apparatus is less likely for the user. 
     To attend to this problem, it is now common for a battery driven information processing apparatus be provided with a so-called resume function to store the contents of a display memory, I/O registers of input/output devices and so on in a main memory, and preserve the contents of the main memory by backing up the same with a battery before turning off the power source such that when the power source is again turned on, the contents of the display memory, the I/O registers of the input/output devices and so on preserved in the main memory are written back to the respective devices, and a state upon turning off the battery is reproduced as if the apparatus had been kept operating. Information processing apparatuses having such a resume function are disclosed, for example, in JP-A-57-17042 and JP A-2-93814. 
     As described above, the resume function provides an excellent information processing apparatus which can reproduce a user&#39;s work state upon again turning on the power source and does not cause the degradation of the usability of the apparatus even if the power source is frequently turned off to reduce the consumption of the battery. However, the resume function hitherto provided in information processing apparatuses does not allow the user to perform another operation while preserving a work state. Also, when a plurality of users use a single information processing apparatus in which a user has preserved a work state using the resume function, another user, when turning on the information processing apparatus, will see the preserved work state of the previous user, thereby presenting unfavorable problems regarding security and utility. 
     Also, since the main memory is backed up by a battery to preserve a work state, the work state can be preserved only for a limited time period the capacity of the battery. 
     Further, the resume function hitherto provided in information processing apparatuses allows the user to reproduce a previous work state only on the same information processing apparatus in which the user interrupted work and preserved the corresponding work state, thereby preventing the user from operating the same work on different apparatus at various locations. 
     The conventional resume function provided in information processing apparatuses further implies a problem that a connection state to a network cannot be correctly reproduced. 
     The conventional resume function provided in information processing apparatus further presents a problem that a message such as electronic mail transmitted through a network cannot be received during an automatic power-off state for reducing power consumption. 
     SUMMARY OF THE INVENTION 
     It is a first object of the present invention to provide an information processing apparatus which is capable of preserving and reproducing a plurality of work states. 
     It is a second object of the present invention to provide an information processing apparatus which is capable of preserving a plurality of work states without backing up a memory with a battery. 
     It is a third object of the present invention to provide an information, processing system which is capable of reproducing a work state on a different information processing apparatus from that in which a user interrupted work and preserved the corresponding work state. 
     It is a fourth object of the present invention to provide an information processing system which is capable of preserving and reproducing a work state on a first information processing apparatus operated by a user using a file in a different information processing apparatus through a network. 
     It is a fifth object of the present invention to provide an information processing apparatus having a resume function which is capable of correctly reproducing a work state upon again turning on the power source even if the information processing apparatus is turned off while connected to another information processing apparatus on a network. 
     It is a sixth object of the present invention to provide an information processing apparatus which is capable of displaying a message sent from another information processing apparatus connected thereto through a network, even if the power source of the information processing apparatus is turned off. 
     The first object is achieved by providing plural sets of work state preservation areas for storing information in a storage unit, and reproducing a work state of the information processing apparatus based on the information in one set of the work state preservation areas specified by the operator from among the plural sets. Since work states at a plurality of times are respectively preserved in the plural sets of the work state preservation areas, respective work states of a plurality of operators or work states of a single operator at a plurality of times are preserved and reproduced. 
     The second object is achieved by preserving work states in a magnetic disk drive or the like which need not be backed up by a battery. Since the work states are preserved in a magnetic disk drive or the like which need not be backed up by a battery, a main memory does not require battery back-up so that no electric power is consumed during power-off state of the information processing apparatus. 
     The third object is achieved by providing plural sets of work state preservation areas in a storage unit of a first information processing apparatus; accessing the storage unit of the first information processing apparatus from a second information processing apparatus through a network; and executing at least processing for storing information on work states at particular times in work state preservation areas and processing for reproducing a work state based on information stored in one set of the work state preservation areas specified by the operator from among the plural sets. Since a plurality of information processing apparatuses are connected to each other through a network, and the work state preservation areas are collectively arranged in a single information processing apparatus, the other information processing apparatuses do not require battery back-up of main memories thereof or installation of a magnetic disk drive or the like. Also, the work state can be reproduced by an information processing apparatus other than that on which the work state was preserved. 
     The fourth object is achieved by executing processing for storing a used state of a file in use through the network when a work state is preserved and processing for reproducing the used state of the file when the work state is reproduced. Even if another information processing apparatus in which a file being used through the network is stored sets this file in an unused state after preserving a work state of the file, since the used state of the file has been stored upon preserving the work state, the used state of the file can be reproduced on the basis of the stored contents upon reproducing the work state. 
     The fifth object is achieved by constantly supplying a network controller with electric power even after preserving a work state, temporarily reproducing the work state when the network controller receives a frame from the network in this state, and performing the necessary processing to maintain a connection state with another information processing apparatus. Since the network controller or a timer is kept supplied with electric power even after preserving the work state, the processing necessary to maintain the connection state with other information processing apparatuses can be continuously performed, thereby making it possible to correctly reproduce the work state when the power source is again turned on. The fifth object is also achieved by constantly supplying the timer with electric power even after preserving a work state, temporarily reproducing the work state when the timer detects the lapse of a specified time in that state, and performing processing necessary to maintain a connection state with another information processing apparatus. Since the network controller or the timer is kept supplied with electric power even after preserving the work state, the processing necessary to maintain the connection state with the other information processing apparatus can be continuously performed, thereby making it possible to correctly reproduce the work state when the power source is again turned on. 
     The sixth object is achieved by constantly supplying the network controller with electric power even after preserving a work state, reproducing the work state when the network controller receives a frame from the network in that state, and displaying a message to be displayed to the user, if included in the frame. Since the network controller is constantly supplied with electric power even after preserving a work state, a frame including a message can be received and the message can be displayed to the user. 
     Therefore, according to the present invention, since a plurality of work states can be preserved and reproduced independently of each other, the user is allowed to perform different work while preserving a particular work state. Since work states of a plurality of users can be preserved and reproduced independently of each other, even if a plurality of users operate a single information processing apparatus to use the resume function, security and utility are not damaged. Also, a work state can be preserved without using a main memory requiring back-up by a battery, which leads to realizing the resume function on an information processing apparatus or the like which does not have a battery back-up function. Since a work state on an information processing apparatus may be preserved in a different information processing apparatus connected thereto through a network, the work state may be reproduced on an information processing apparatus different from that on which the user interrupted a work and preserved the work state, thereby providing an information processing apparatus which allows the user to operate the same work at various locations. Even if an information processing apparatus is logically connected with another one through a network, a work state can be correctly preserved and reproduced, which enables the utilization of excellent features provided by the resume function, such as improvement of user-friendly operation and reduction in power consumption, in an information processing apparatus connected to a network. Further, even when an information processing apparatus is temporarily turned off while connected to a network for the purpose of reduction in power consumption, it is automatically turned on again to display a message, if arriving at the user, whereby the resume function can be utilized without damaging the serviceability provided by an information processing apparatus connected to a network such as for electronic mail and message transmission function and so on. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be more apparent from the following detailed description, when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  illustrates an example of stored contents of a main memory in a first embodiment of the present invention; 
         FIG. 2  is a block diagram illustrating the configuration of an information processing apparatus according to the first embodiment of the present invention; 
         FIG. 3  is a flow chart of programs for realizing a resume function according to the first embodiment of the present invention; 
         FIG. 4  is a block diagram illustrating the configuration of an information processing apparatus according to a second embodiment of the present invention; 
         FIG. 5  illustrates an example of a format of a work state preserving file in the second embodiment of the present invention; 
         FIG. 6  is a block diagram illustrating the configuration of a network according to a third embodiment of the present invention; 
         FIG. 7  is a flow chart illustrating an example of an interrupt program for performing a work state preservation in a fourth embodiment of the present invention; 
         FIG. 8  is a flow chart illustrating an example of an interrupt program for performing work state preservation in a fifth embodiment of the present invention; 
         FIG. 9  is a flow chart illustrating an example of a reset program for performing work state reproduction in the fifth embodiment of the present invention; 
         FIG. 10  is a block diagram illustrating the configuration of a network according to the fifth embodiment of the present invention; 
         FIG. 11  illustrates a memory map of a main memory in the fifth embodiment of the present invention; 
         FIG. 12  illustrates an example of a format for a work state preservation file in the fifth embodiment of the present invention; 
         FIG. 13  illustrates an example of a format for a work state preservation file in a sixth embodiment of the present invention; 
         FIG. 14  illustrates an example of a screen for inputting a work state name in the first embodiment; 
         FIG. 15  illustrates an example of an inquiry screen in the fourth embodiment of the present invention; 
         FIG. 16  illustrates an example of a screen for inputting a work state preservation file name; 
         FIG. 17  illustrates an example of a screen for inputting a user&#39;s name and a password in the fifth embodiment of the present invention; 
         FIG. 18  illustrates an example of a screen for displaying a message announcing that an apparatus presently in use is different from an apparatus on which a work state was preserved in the fifth embodiment of the present invention; 
         FIG. 19  illustrates an example of a screen for displaying a message indicating modified file contents in the fifth embodiment of the present invention; 
         FIG. 20  illustrates an example of a file directory according to a seventh embodiment of the present invention; 
         FIG. 21  illustrates an example of a screen for inputting a work state preservation command in the seventh embodiment of the present invention; 
         FIG. 22  is a block diagram illustrating the configuration of an information processing apparatus according to an eighth embodiment of the present invention; 
         FIG. 23  is a block diagram illustrating the configuration of an information processing system according to one embodiment of the present invention; 
         FIG. 24  is a schematic diagram illustrating the configuration of a power supply controller used in the information processing apparatus according to the eighth embodiment of the present invention; 
         FIG. 25  is a sequence diagram representing power-off processing in the eighth embodiment of the present invention; 
         FIG. 26  is a sequence diagram representing processing for receiving a connection acknowledgment request frame in the eighth embodiment of the present invention; 
         FIG. 27  is a sequence diagram representing processing for again turning on the power source in the eighth embodiment of the present invention; 
         FIG. 28  is a block diagram illustrating the configuration of an information processing apparatus according to a ninth embodiment of the present invention; 
         FIG. 29  is a sequence diagram representing processing for transmitting a connection acknowledgement notice frame in the ninth embodiment of the present invention; and 
         FIG. 30  is a sequence diagram representing message receiving processing in a tenth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A first embodiment of the present invention will hereinafter be described with reference to  FIGS. 1 ,  2  and  3 . 
       FIG. 2  illustrates the configuration of a battery driven information processing apparatus of the present embodiment which comprises a CPU  1 ; a main memory  2  employing DRAM devices; a display controller  3 ; a display memory  4 ; a liquid crystal display  5 ; a ROM  6 ; a battery  7 ; a memory controller  8 ; a power supply controller  9 ; a power supply switch  10  for resume function; a main power supply switch  11 ; a keyboard  12 ; a keyboard controller  13 ; an address/data bus  14 ; a power supply line  20  for back-up; an SRAM  21 ; and an interrupt signal line  22 . 
     The power supply controller  9  monitors a state of the power supply switch  10  for the resume function, a state of the battery  7 , and the keyboard controller  13 . If the power supply controller  9  detects, in a power-on state, that a user has depressed the power supply switch  105  for resume function, that the battery  7  has been used up, or that no input has been provided from the keyboard  12  for a predetermined amount of time, the power supply controller  9  so informs the CPU  1  through the interrupt signal line  22 . The CPU  1 , upon detecting the interrupt signal, executes an interrupt processing program  50  which has been previously written in the ROM  6 . The processing contents of the interrupt processing program will be explained below with reference to a flow chart of  FIG. 3 . First, at step  51  for preservation of CPU register contents, the contents of registers in the CPU  1  are written into the main memory  2 . Next, at step  52  for preservation of I/O register contents in peripheral devices, the contents of I/O registers in peripheral devices including the display controller  3  and the keyboard controller  13  are read out and stored in the main memory  2 . Further, display data stored in the display memory  4  is read out and stored in the main memory  2  at step  53  for preservation of display memory contents. At step  54  for setting a preserved work name, the user is prompted to input a preserved work name which is written into the main memory  2 . An example of a displayed screen for inputting a preserved work name is shown in  FIG. 14 . Also, at step  54  for setting a preserved work name, a value indicating that work state preservation has been completed is written into a resume flag register provided in the power supply controller  9 . Next, at step  55  for power-off processing, the CPU  1  controls the power supply controller  9  so that the power supply controller  9  itself stops supplying electric power to devices other than the SRAM  21  and the memory controller  8  to set the apparatus in the power-off state. In this state, a minimum refresh operation required to preserve the stored contents in the main memory  2  constituted of DRAM devices is solely performed by the memory controller  8 , whereby the battery  7  will not substantially be consumed. 
       FIG. 1  illustrates an example of stored contents in the main memory  2  of the first embodiment. The user is allowed to execute an operating system (OS) and an application program using an area from 000000H to 17FFFFH. Here, “H” is a suffix indicative of a hexadecimal number. Data saved by the interrupt processing program  50  is written into an address area from 180000H to 1FFFFFH. In this embodiment, in addition to the preservation area A  101  from 18000H to 1FFFFFH, areas from 200000H to 3FFFFFH and from 400000H to 5FFFFFH are also used as preservation areas B  102  and C  103  such that three kinds of work states can be simultaneously preserved. It should be noted that the addresses and data may be located in a manner different from that shown in  FIG. 1 . 
     When the power supply controller  9  detects in power-off state that the user has again depressed the power supply switch  10  for the resume processing function, the power supply controller  9  resumes the supply of electric power to all of the devices. In this operation, the CPU  1  first executes a reset program  60  stored in the ROM  6 . As shown in  FIG. 3 , the reset program  60  first reads out the value of the resume flag register provided in the power supply controller  9  to check whether state preservation was performed upon turning off a power source at step  61  for state preservation check. If the result of the check shows that state preservation was not performed upon turning off the power source, a step  63  for initial setting is executed to check and initialize the main memory  2 , the peripheral devices and the whole apparatus similarly to an information processing apparatus which does not have a resume function, and the apparatus is set in a state of waiting for the user to start a program. Conversely, if the check result shows that state preservation was performed upon turning off the power source, the user is prompted to input the preserved work name at step  62  for inputting a preservation area. Then, at step  64  for preserved area check, it is checked in which of the preservation areas in  FIG. 1  that data related to the input preserved work name exists. If the work data specified by the preserved work name is preserved in an area other than the preservation area A  101  in the addresses from 000000H to 1FFFFFH, the work data is replaced with the contents in the preservation area A  101  at step  65  for replacement with the preservation area A. For example, if the preserved work name indicates the preservation area B  102  is at step  64  for preservation area check, the contents of the addresses from 000000H to 1FFFFFH are copied to the addresses from 200000H to 3FFFFFH, while the contents of the addresses from 200000H to 3FFFFFFH are copied to the addresses from 000000H to 1FFFFFFH. If the result of the check  64  shows that the preserved area is the preservation area A  101 , the replacement with the preservation area A at step  65  is not executed. At step  66  for restoring the contents of the display memory, the contents of the display memory in the preservation area A  101  are read out and written into the display memory  4 . At step  67  for restoring the contents of the I/o registers in the peripheral devices, values in the I/O registers of the peripheral devices including the display controller  3  and the keyboard controller  13  are read out from the preservation area A  101  and written into the I/O registers of the display controller  3 , the keyboard controller  13  and so on, respectively. Further, at step  68  for restoring the contents of the CPU registers, the contents of the registers in the CPU  1  preserved in the preservation area A  101  are written into the respective registers in the CPU  1 . As a result of the above described processing, a work state specified by the user can be reproduced within one or a plurality of work states previously interrupted by a power-off executed by the interrupt. Incidentally, part of preserved data for the work states may be stored in the SRAM  21  not in the main memory  2 . 
     While the above embodiment shows an example where the user can arbitrarily specify a preserved work name, a user&#39;s ID may be used as the preserved work name. The use of the user&#39;s ID can prevent a work state preserved by a particular user from being reproduced by another user who turns on the information processing apparatus, thereby making it possible to realize a resume function that has excellent security features. Also, the user&#39;s ID may be combined with a name arbitrarily specified by the user such that each user is allowed to preserve and reproduce a plurality of work states. This alternative can be achieved by preserving the user&#39;s ID in place of a preserved work name together with a work state or preserving a work state in a preservation area corresponding to the user&#39;s ID. In the latter case, the information processing apparatus requires the user to input the user&#39;s ID when the power source is turned on. Then, it is checked whether or not a work state corresponding to the inputted user&#39;s ID exists in the memory. If the check result shows that a work state corresponding to the input user&#39;s ID exists, the user is further requested to input a preserved work name, followed by the reproduction of the work state from a preservation area specified by the user in a similar manner. Thus, work states of a plurality of users can be simultaneously preserved, and when an associated user turns on the power source, his or her own work state can be reproduced without causing any security problems. 
     Next, a second embodiment of the present invention will be described with reference to  FIGS. 4 and 6 .  FIG. 4  illustrates an exemplary configuration of an information processing apparatus according to the second embodiment. The second embodiment differs from the first embodiment shown in  FIG. 2  in that a magnetic disk drive  16   a  and a disk controller  15  for controlling the magnetic disk drive  16   a  are provided and the power supply line  20  for back up and the SRAM  21  are removed. In this embodiment, work states which are preserved in the main memory  2  in the first embodiment are preserved in the magnetic disk drive  16   a.    
     In this event, the contents of the main memory  2  are also saved in the magnetic disk drive  16   a . Specifically, data in respective preservation areas in the main memory  2  in the first embodiment are preserved in the magnetic disk drive  16   a  as a work state preservation file  200 .  FIG. 5  illustrates an example of a format of the work state preservation file  200 . The work state preservation file  200  may be designated a file name which includes a preserved work name specified by the user or a user&#39;s ID such that a plurality of work states of one or plural users can be preserved and reproduced when an associated user turns on the power source without causing any security problem. Additionally, in the second embodiment, since work states are preserved in the magnetic disk drive  16   a  which does not require a back-up operation by a battery, the main memory  2  need not be backed up by a battery, and many work states can be preserved over a long term. 
     Next, a third embodiment of the present invention will be described below with reference to  FIG. 6 . A network shown in  FIG. 6  comprises a first information processing apparatus  17   a  which the user operates using application software and so on; a second information processing apparatus  17   b  provided with a magnetic disk drive  16   b ; and a third information processing apparatus  17   c  having the same architecture as the first information processing apparatus  17   a . The magnetic disk drive  16   b  can be accessed from the first information processing apparatus  17   a  and the third information processing apparatus  17   c  through network adapters  18   a ,  18   b  and  18   c , and a network transmission line  19 . 
     The third embodiment differs from the second embodiment in that a work state preservation file  200  of the first information processing apparatus  17   a  is not stored in an internal storage unit of the information processing apparatus  17   a  but in the second information processing apparatus  17   b  connected thereto through the network. The third embodiment features that the first information processing apparatus  17   a  does not necessarily require a battery back-up function for the main memory  2  to preserve work states and the magnetic disk drive  16   a  which need not be backed up by a battery. Also, since it is not necessary to turn off the second information processing apparatus  17   b  in association with the first information processing apparatus  17   a , a main memory or the like in the second information processing apparatus  17   b  may be used in place of the magnetic disk drive  16   b  if the second information processing apparatus  17   b  is not turned off. 
     In this case, when the first information processing apparatus  17   a  is turned off, a work state of the first information processing apparatus upon turning off the power source is transferred to the second information processing apparatus  17   b  connected thereto through the network. The second information processing apparatus  17   b , responsive to this, stores and preserves the transferred work state in the main memory thereof or in the magnetic disk drive  16   b . In this manner, the first information processing apparatus  17   a  can realize the resume function without its main memory being backed up by a battery. In addition, a work state preserved in the second information processing apparatus  17   b  may be reproduced by the third information processing apparatus  17   c . Therefore, a work state may be preserved by the first information processing apparatus  17   a  and reproduced from the third information processing apparatus. 
     Next, a fourth embodiment of the present invention will be described below with reference to  FIG. 7 . The fourth embodiment provides an interrupt processing program  50   a  by adding steps  701 ,  702 ,  703 ,  704  and  705  as shown in  FIG. 7  to the interrupt processing program explained in connection with  FIG. 3  in the first embodiment in order to solve a problem that a network connection state upon preserving a work state cannot be correctly reproduced when the work state is to be reproduced. First, at step  701 , it is checked whether an associated information processing apparatus is connected to a network. If the information processing apparatus is not connected to the network, the program proceeds to the step  51  for preserving the contents of the CPU registers to subsequently preserve a work state and turn off the power source in the completely same manner as the first embodiment. On the other hand, if the information processing apparatus in question is connected to the network, it is checked at step  702  whether the interrupt processing program  50   a  has been started by a timer interrupt due to the fact that no input had been given from a keyboard  12  for a predetermined amount of time. If the timer interrupt has caused the interrupt processing program  50   a  to start, the interrupt processing program  50   a  is terminated without executing subsequent steps. If the timer interrupt is not the cause, the user is informed at step  703  that a network connection state cannot be reproduced, and then at step  704  the user is asked whether or not the work state should be preserved. An example of a displayed screen for this inquiry is shown in  FIG. 15 . If the user answers that the work state will not be preserved, the user is again asked at step  705  whether or not the power source is turned off. If the user answers that the power source will be turned off, power-off processing at step  55  is executed, and otherwise the interrupt processing program  50   a  is terminated without performing other processing. If the user answers at step  704  that the work state should be preserved, the steps  51  to  55  are executed to perform the preservation of the work state and the power-off processing in the completely same way as the first embodiment. 
     As described above, when the information processing apparatus is connected to the network, a work state is not preserved by the timer so as to prevent the preservation operation from being automatically executed for a network connection state which is rendered unreproducable due to the user who has interrupted the operation of the information processing apparatus for a while. Further, when the user is going to manually execute the work state preservation, the user is informed that the network connection state cannot be reproduced, whereby the user is led to perform appropriate processing. 
     Next, a fifth embodiment of the present invention will be described with reference to  FIG. 10 . The configuration of a system according to the fifth embodiment shown in  FIG. 10  comprises a first information processing apparatus  17   a  which the user operates using application software and so on; a second information processing apparatus  17   b  provided with a magnetic disk drive  16   b  for acting as a server; a third information processing apparatus  17   c  having the same architecture as that of the first information processing apparatus  17   a ; and a fourth information processing apparatus  17   d  having an architecture different from that of the first information processing apparatus  17   a . The magnetic disk drive  16   b  is accessible from the first, third and fourth information processing apparatus  17   a ,  17   c  and  17   d  through network adapters  18   a ,  18   b ,  18   c  and  18   d  and a network transmission line  19 . The hardware configuration of the information processing apparatus of the fifth embodiment is assumed to be the same as that of the first embodiment shown in  FIG. 2 . Now, the operation of the system will be explained in connection with preservation and reproduction of a work state in this order. 
     A power supply controller  9  of the information processing apparatus  17   a  monitors a state of a power supply switch  10  for the resume function, a state of a battery  7  and a keyboard controller  13 . If the power supply controller  9  detects, in power-on state, that a user depresses the power supply switch  10  for resume function, that the battery  7  has been used up, or that no input has been provided from a keyboard  12  for a predetermined time period, the power supply controller  9  informs a CPU  1  of the occurrence of the state as mentioned above through an interrupt signal line  22 . The CPU  1 , upon detecting the interrupt signal, executes an interrupt processing program  50   b  which has previously been written in a RON  6 . The processing executed by the interrupt processing program  50   b  will be explained below with reference to a flow chart of  FIG. 8  and a memory map of  FIG. 11 . First, at step  801 , the contents of registers in the CPU  1  are stored in a CPU register table  1010 . The CPU register table  1010  is composed of data sets each consisting of a register number, a size indicative of a number of bytes of a related register, and CPU register data indicative of the contents of the register, which are repeated by a number equal to the number of the registers, as shown in  FIG. 11 . Stored in a CPU register table address  1004  is the start address of the CPU register table address  1010 . 
     Next, at step  802 , the I/O registers are read out, and an I/O register table  1011  and an I/O register table address  1005  shown in  FIG. 11  are stored in the main memory  2 . The I/O register table  1011  is composed of data sets each consisting of an I/O address, a size indicative of a number of bytes of the register, and I/O register data indicative of the contents of the register, which are repeated by a number equal to the number of the registers. Stored in the I/O register table address  1005  is the start address of the I/O register table address  1011 . 
     Next, the contents of the display memory  4  are read out and stored in a display memory data table  1012  at step  803 . The start address of the display memory data table  1012  is stored in a display memory table address  1006 . 
     At step  804 , an open file information table  1013  is created. The open file refers to a file being used by the OS for the operation of the OS itself or by a request from application software. The state of an open file is one of read-only, write-only and read/write states. The open file information table  1013  created herein is such one that includes information sets each consisting of the name of an opened file, a state of the opened file and the number of bytes of the file name and a flag indicative of the state, which are repeated by a number equal to the number of opened files. The start address of the open file information table  1013  is stored in an open file information table address  1007 . 
     Next, it is checked at step  805  whether the first information processing apparatus  17   a  in which this program is being executed is physically and logically connected to the second information processing apparatus  17   b  acting as a server through the network. If the check result shows that the first information processing apparatus  17   a  is connected to the second information processing apparatus  17   b , subsequent steps  806 ,  807  are executed, and otherwise step  815  is executed. At step  806 , an opened server file is closed referring to the open file information table  1013  created at step  804 , and at step  807  a logical name of the second information processing apparatus  17   b  in the network is stored in the main memory  2  as a connected server name  1014  as shown in  FIG. 11 . At this time, the stored address of the connected server name  1014  in the main memory  2  is stored in the main to memory  2  as a connected server name address  1008 . On the other hand, at step  815 , the connected server name address  1008  is set to “0” which indicates that the first information processing apparatus  17   a  is not connected to the server. 
     At step  808 , the user is asked whether a work state is preserved in a file or in the main memory backed up by a battery. If the user selects the preservation of the work state in a file, the user is prompted to input the name of a file in which the work state is to be preserved at step  809 .  FIG. 16  illustrates an example of a screen on which the Inquiries of the steps  808 ,  809  are displayed. Next, a work state preservation file  200   a  designated by the input file name is created at step  810 . At this time, in addition to data contents  203  in the main memory  2  shown in  FIG. 11 , a preserved machine type code  201  and a preservation executed date  202  are also stored in the work state preservation file  200   a . The structure of the work state preservation file  200   a  is illustrated in  FIG. 12 . Turning back to the flow chart of  FIG. 8 , a resume flag register provided in the power supply controller  9  is set to a value indicating that the work state is not preserved, when it is to be preserved in the file (step  811 ). Conversely, when the work state is not to be preserved in the file, the resume flag register is set to a value indicating that the work state has been preserved (step  812 ). Afterward, log-out is executed to disconnect the information processing apparatus  17   a  from the network at step  813 , and power-off processing is performed at step  814 , followed by the termination of the interrupt processing program  50   b  for preserving a work state. 
     Next, explanation will be given of the operation when a work state is reproduced. When the power supply controller  9  detects that the user has again depressed the power supply switch  10  for the resume function in power-off state, the power supply controller  9  starts supplying all devices with electric power. This enables the CPU  1  to first execute a reset program  60   b  stored in the ROM  6 .  FIG. 9  illustrates a flow chart of the reset program  60   b . The reset program first reads out the value set in the resume flag register in the power supply controller  9  at step  901  to check whether a work state was stored in the main memory  2  upon turning off the power source. If the check result shows that a work state was preserved in the main memory  2 , the control is transferred to step  912 . Otherwise, step  902  is executed. At step  902 , the user is asked whether or not the work state is to be reproduced from the file. If the user answers that the work state will not be reproduced from the file, the control is transferred to step  900  for initial setting where the information processing apparatus is initialized and the OS is started. If the user answers at step  902  that the work state will be reproduced from the file, the user is prompted to input the name of the work state preservation file  200   a  which is to be used. An example of a displayed screen at this time is shown in  FIG. 16 . Next, at step  904 , the input name of the work state preservation file  200   a  is analyzed to check whether this is a file on the information processing apparatus  17   b  which is used as a server. If the check result shows that it is not a file on the information processing apparatus  17   b , the control is transferred to step  908 . Conversely, if that file is a file on the information processing apparatus  17   b , the network adapter  18   a  is initialized at step  905 , the user is prompted to input the user name and a password at step  906 , and log-in is executed to the information processing apparatus  17   b  using the user name and the password at step  907  to achieve a logical connection. An example of a display on the screen at step  906  is shown in  FIG. 17 . Next, the work state preservation file  200   a  is referenced at step  908  to read out the preserved machine type code  201  stored when the work state was preserved. Then, it is checked at step  909  whether or not the preserved machine type code  201  coincides with the machine type code of the information processing apparatus which is executing this program. As has been already described, in this embodiment, while the information processing apparatus  17   a  and the information processing apparatus  17   b  have the same architecture and the same machine type code, the information processing apparatus  17   d  has a different architecture and a different machine type code from the information processing apparatus  17   a ,  17   b . Therefore, assuming that a work state was preserved on the information processing apparatus  17   a , if this work is to be reproduced on the information processing apparatus  17   a  or  17   c , the determination at step  909  indicates “coincidence.” On the other hand, if the work state is reproduced on the information processing apparatus  17   d , the determination is “dissidence.” If “dissidence” is indicated by the check result, the user is informed of the difference in machine type as well as inquired whether or not another work state preservation file  200   a  is used at step  910 . A screen for this inquiry is shown in  FIG. 18 . If the user answers that another work state preservation file  200   a  is used, the returns to step  903 . If the user answers that file is used, the control is transferred to the initialization step  900  for initializing the information processing apparatus and starting the OS without performing the work state reproducing processing. If “coincidence” is indicated by the determination result at step  909 , the main memory contents  203  in the work sate preservation file  200   a  are read out and stored in the main memory  2 . As a result, the contents of the main memory  2  shown in  FIG. 11  are reproduced. Next, at step  912 , the contents of the connected server name address  1008  are checked, and if “0” is set therein, it is determined that the information processing apparatus  17   b  was not connected to the network when the work state was preserved, thus transferring the control to step  918 . If the contents of the connected server name address  1008  is not “0,” it is determined that the information processing apparatus  17   b  was connected to the network, and the initialization of the network adapter  18   a  is executed at step  913 . Next, whether the user name was input is checked at step  914 . If the user name was not input, the user is prompted to input the user name and a password at step  915 , and log-on to the information processing apparatus  17   b  is executed at step  916  using the input user name and the password. Next, the open file information table  1013  on the main memory  2  is referenced at step  917 . If the table contains a file on the information processing apparatus  17   b  used as a server, an open state of that file is reproduced. At step  918 , the latest modified date of the file registered in the open file information table  1013  is checked and compared with the preserved date  202  of the work state preservation file  200   a . If the latest modified date is later than the preserved date  202 , there is a possibility that the contents of the file were modified after the work state had been preserved. Therefore, the file cannot be used as it is so that a message as shown in  FIG. 19  is displayed to draw the user&#39;s attention. Next, the contents of the display memory data table  1012  are stored in the display memory  4  at step  919 , and the I/O register table  1011  is referenced at step  920 , thereby reproducing the contents of the respective I/O registers. Finally, at step  921 , the CPU register table  1010  is referenced to reproduce the contents of the respective registers in the CPU  1 . Upon termination of the step  921 , the reproduction of the work state is completed. 
     In the fifth embodiment, when the information processing apparatus has been connected to the network upon preserving a work state, the connection to the network and log-in operation are automatically performed upon reproducing the work state, thereby making it possible to reproduce the work state including the connection state to the network. Also, even when a work state is preserved while a file on another information processing apparatus used as a server is open, this open state can also be reproduced upon reproducing the work state, thereby correctly reproducing the work state. Further, when an open state of a file is to be reproduced, the work state preserved date is compared with the latest modified date of the file, and if the latest modified date is later, the user is informed that the contents of the file have been modified after the work state was preserved, whereby the user can effect necessary proceedings to the file. Also, the machine type code  201  of an information processing apparatus on which a work state was preserved is stored in the work state preservation file  200   a  and is compared, upon reproducing the work state, with the machine type code of an information processing apparatus on which the work state is to be reproduced. If these two codes are different, the reproduction of the work state is cancelled, thereby preventing troubles such as run-away of a program which may possibly occur when the work state is reproduced on an information processing apparatus of a different type. Since the user is allowed to select whether the work state is preserved in the main memory backed up by a battery or in the work state preservation file  200   a , an optimal work state preserving method can be selected according to a particular situation, such as whether or not the information processing apparatus is connected to the network, whether high speed preservation and reproduction are enabled only for a single set of work state by the main memory  2  backed up by a battery, and so on. 
     Next, a sixth embodiment of the present invention will be described below with reference to  FIG. 13 . A work state preservation file  200   b  of  FIG. 13  shows another example of the work state preservation file  200   a  in the fifth embodiment. While the contents of the main memory  2  are stored as they are as the contents  203  of the main memory in the fifth embodiment, contents of memory blocks being used in the main memory  2  are solely stored as contents  203   b  of the main memory in the sixth embodiment. Specifically, based on memory using situation data proposed by the OS, the start address, block size and contents of the main memory are stored for every memory block in use. This removes the necessity of storing data in unused portions of the main memory, thereby reducing the file size of the work state preservation file  200   b , decreasing the amount of the magnetic disk  16   a  or  16   b  used for storing the work state preservation file  200   b , and shortening a time necessary for preservation and reproduction. For storing the contents of the main memory  2  into the work state preservation file  203   b , a data compress algorithm or the like may be used to reduce the file size of the work state preservation file  203   b  other than the above-stated method which imitatively stores memory blocks in use. 
     Next, a seventh embodiment of the present invention will be described below. In this embodiment, the interrupt program for preserving a work state and the reset program for reproducing a work state, which are stored in the ROM  6  in the foregoing embodiments, are stored in a storage unit as program files which can be executed as commands from the OS.  FIG. 20  illustrates a file directory of a magnetic disk  16   a  employed in an information processing apparatus  17   a  of the seventh embodiment. Stored in the file directory are two kinds of OS&#39;s: OSa and OSb. OSa and OSb are different in command program type so that a common program file cannot be used. Commands and data for the respective OS&#39;s are stored under the directories of commands  502   a ,  502   b  and the directories of data  503   a ,  503   b , respectively. A work state reproduction program and a work state preservation program for OSa are stored in the directory of the command  502   a  as files named “work state reproduction a”  504   a  and “work state preservation a”  505   a , respectively. A work state reproduction program and a work state preservation program for OSb are stored in the directory of the command  502   b  as files named “work state reproduction b”  504   b  and “work state preservation b”  505   b , respectively. Processing executed by the work state preservation a  505   a  and the work state preservation b  505   b  may be the same as the processing procedures of the foregoing interrupt programs  50 ,  50   a ,  50   b  and so on. Likewise, processing executed by the work state reproduction a  504   a  and the work state reproduction b  504   b  may be the same as the processing procedures of the foregoing reset programs  60 ,  60   b  and so on. When the user desires to preserve/reproduce a work state, work state preservation/reproduction programs in accordance with the kind of an OS in use are executed as commands.  FIG. 21  illustrates an example of a screen in which another window is opened to issue a command for preserving a work state while a graph is being created in a window under the control of OSa. 
     According to the seventh embodiment, since the work state preservation and reproduction programs can be executed as command programs, information processing apparatus having no power supply mechanism or RON programs for the resume function can also realize the resume function. Since work state preservation and reproduction programs can be selected in accordance with the kind of a used OS, the preservation and reproduction of a work state can be easily achieved even when a plurality of OS&#39;s are used. 
     While the foregoing embodiments show examples where a magnetic disk drive is employed as a storage unit which need not be backed up by a battery, an optical disk drive or the like may be replaced therewith as long as it does not require battery back-up. The display unit may be a CRT or the like other than the liquid crystal display  5 . Further, a work state may be saved and reproduced not only when the power source is turned off and again turned on, but also at an arbitrary timing at which the user desires to interrupt or resume a work. 
     Next, an eighth embodiment of the present invention will be described with reference to  FIGS. 22-27 . 
       FIG. 23  illustrates the configuration of an information processing system employing information processing apparatus according to one embodiment of the present invention. In this information processing system, an information processing apparatus  17   a  is permitted to read from and write into a disk drive  16   b  connected to an information processing apparatus  17   b , as if it were a disk unit connected thereto, by establishing a logical connection with the information processing apparatus  17   b  through a network  19 . While the logical connection is maintained between the information processing apparatus  17   a  and  17   b , the information processing apparatus  17   b  periodically transmits a connection acknowledgement request frame to the information processing apparatus  17   a  at appropriate time intervals, and the information processing apparatus  17   a  returns a connection acknowledgement response frame responsive to the connection acknowledgement request frame, thereby maintaining the logical connection therebetween. Alternatively, the information processing apparatus  17   a  periodically transmits a connection acknowledgement notice frame to the information processing apparatus  17   b  at appropriate time intervals to maintain the logical connection. If the connection acknowledgement response frame is not returned, or if the connection acknowledgement notice frame is not transmitted, the information processing apparatus  17   b  assumes that the information processing apparatus  17   a  is in a failure state and releases the logical connection. 
       FIG. 22  illustrates the configuration of an information processing apparatus  17   a  implementing the eighth embodiment of the present invention. In the drawing, reference numeral  23  designates a power supply control signal line from a network controller  18  to a power supply controller  9 .  FIG. 24  illustrates in greater detail the configuration of the power supply controller  9 . The power supply controller  9  comprises a switch  91  for turning on and off electric power supplied to respective sections of the controller  9 ; a power supply switch controller  92  for controlling the switch  91 ; a status register  93  for noticing a status of the power supply controller  9  to a CPU  1 ; a command register  94  for the CPU  1  to instruct the power supply controller  9  of a certain operation; a timer  95  used by the power supply switch controller  9  for timing; and a power supply line  96  for supplying electric power to the respective sections. In the information processing apparatus thus constructed, the resume function according to the present invention operates in the following manner. 
     First, a procedure of the information processing apparatus  17   a  in operation for preserving a work state at a certain time and shutting off the power supply will be explained with reference to a sequence diagram of  FIG. 25 . When the power supply controller  9  detects,  20  while the information processing apparatus  17   a  is operating, that the power supply switch  10  for resume function is depressed, that the voltage of the battery  7  has decreased below a predetermined value, or that no key input has been provided through the keyboard  12  for a predetermined amount of time, the power supply switch controller  92  generates an interrupt signal to the CPU  1  through the interrupt signal line  22  for requesting the CPU  1  to start necessary processing for turning of f a power source (step  101 ). The CPU  1 , upon receiving the interrupt, starts work state preservation processing (step  102 ). A method of preserving a work state may be a method of preserving the work state including the contents of the display memory  4  and so on such that the work state is stored in the RAM  2  composed of RAM devices which can be backed up by the battery  7 ; a method of preserving the work state in the disk drive  16   a  as a file; a method of preserving the work state as a file in the disk drive  16   b  connected to the information processing apparatus  17   b  through the network  19 ; and so on. The CPU  1 , upon completing the preservation of the work state, writes a particular command indicative of the completion of the work state preservation in the command register  94  to inform the power supply switch controller  92  of the completion of the work state preservation processing (step  103 ). The power supply switch controller  92 , when informed of the completion of the work state preservation processing, operates the switch  91  to stop supplying electric power to the respective sections of the information processing apparatus  17   a  except for the network controller  18 , and informs the network controller  18  of the power-off state (step  104 ). When the network controller  18  receives a frame, it does not immediately notify the CPU  1  but rather it notifies the power supply controller  9 . By the foregoing processing, the information processing apparatus  17   a  preserves the work state and falls into power-off state. 
     Next explained is a procedure for responding to a connection acknowledgement request frame transmitted from the information processing apparatus  17   b  when the information processing apparatus  17   a  has preserved a work state and remains in power-off state. 
     Referring to a sequence diagram of  FIG. 26 , if a connection acknowledgement request frame is transmitted from the information processing apparatus  17   b  while the information processing apparatus  17   a  remains in the power-off state, the network controller  18  reserves a frame reception interrupt to the CPU  1  and issues a power-on request to the power supply controller  9  through the power supply control signal line  23  (step  111 ). The power-on request is received by the power supply switch controller  92  in the power supply controller  9  which sets in the status register  93  a value indicating that this power-on requires the reproduction of the work state and operates the switch  91  to supply electric power onto the power supply line  96  (step  112 ). It should be noted however that since this is the second temporary power-on requested by the network controller  18 , electric power is not supplied up to the display unit  5 . The CPU  1 , supplied with electric power, starts reset processing using the program stored in the ROM  6 . The CPU  1 , after the power-on, first reads the contents of the status register  93  to recognize the necessity of the reproduction of the work state and starts the work state reproduction processing (step  113 ). Upon completing the reproduction of the work state, the CPU informs the power supply controller  9  of the completion of the work state reproduction by writing a particular command into the command register  94  and goes on with processing from the reproduced work state at the power-off time (step  114 ). The power supply controller  9 , when informed of the completion of the work state reproduction processing, informs the network controller  18  of the same, and starts the timer  95  (step  115 ). The network controller  18 , when informed of the completion of the work state reproduction processing, now issues the reserved frame reception interrupt to the CPU  1  (step  116 ). Then, the CPU  1 , upon receiving the frame reception interrupt, starts protocol processing. In this processing, since the received frame is a connection acknowledgement request frame from the information processing apparatus  17   b , the CPU  1  requests the network controller  18  to transmit a connection acknowledgement response frame (step  117 ) The frame transmission request from the CPU  1  causes the network controller  18  to transmit the connection acknowledgement request frame to the information processing apparatus  17   b  (step  118 ). Afterward, when the timer  95  started at step  115  expires, the power supply switch controller  92  is so notified and responsively generates an interrupt to the CPU  1  through the interrupt signal line  22  for requesting the CPU  1  to start necessary processing for power-off (step  119 ). The CPU  1 , upon receiving the interrupt, again starts the processing for preserving a work state (step  120 ). When the work state preservation processing is completed, the CPU  1  notifies the power supply controller  9  of the completion of the work state preservation by writing a particular command into the command register  94  (step  121 ). This notification is received by the power supply switch controller  92  in the power supply controller  9  which in turn operates the switch  91  to stop supplying electric power to the respective sections of the information processing apparatus  17   a  and informs the network controller  18  of the second power-off state of the information processing apparatus  17   a  (step  122 ). The foregoing processing permits the information processing apparatus  17   a , even in power-off state, to respond to the connection acknowledgement request frame transmitted from the information processing apparatus  17   b  by temporarily turning on the power source upon receiving the frame, thereby making it possible to maintain the logical connection with the information processing apparatus  17   b.    
     Finally explained is a procedure of second turn-on of the power source by request from the user when the information processing apparatus  17   a  preserved a work state and remains in power-off state. 
     Referring to a sequence diagram of  FIG. 27 ,  25  when the power supply switch  10  for resume function is depressed in power-off state, the power supply switch controller  9  sets in the status register  93  a value indicating that this power-on requires reproduction of the work state, and operates the switch  91  to start supplying electric power onto the power supply line  96  (step  131 ). Since this second power-on was required by the user, all of the sections including the display unit  5  of the information processing apparatus  17   a  are supplied with electric power. The CPU  1 , supplied with electric power, starts the reset processing using the program stored in the ROM  6 . After the power-on, the CPU  1  first reads the contents of the status register  93  to recognize the necessity of work state reproduction and starts the work state reproduction processing (step  132 ). Upon completing the reproduction of the work state, the CPU  1  informs the power supply controller  9  of the completion of the work state reproduction by writing a particular command into the command register  94 , and goes on with the processing from the reproduced work state at the power-off time (step  133 ). The power supply controller  9 , when informed of the completion of the work state reproduction processing, notifies this to the network controller  18  (step  134 ). Since this is a second power-on requested by the user, the timer  95  is not started. The notification causes the network controller  18  to immediately notify the CPU  1  with an interrupt when it receives a frame at a later time. The foregoing processing permits the user to reproduce the work state when the power source was turned off and proceeds to the work from that state. 
     Next, a ninth embodiment of the present invention will be described with reference to  FIGS. 28 and 29 . 
       FIG. 28  illustrates the configuration of an information processing apparatus  17   a  according to the ninth embodiment of the present invention. In the drawing, reference numeral  24  designates a timer for detecting the lapse of a specified time. 
     In the operations of the resume function according to this embodiment, a procedure of the information processing apparatus  17   a  for preserving a work state and falling into the power-off state and a procedure of again turning on the power source by request of the user are identical to those represented by the sequence diagrams shown in  FIGS. 25 and 27 , respectively, provided the network controller  18  is replaced with the timer  24 . When informed of the power-off state, the timer  24  does not immediately notify the lapse of a specified time to the: CPU  1  but to the power supply controller  9 , whereas, when informed of release of the power-off state, the timer  24  returns to immediately notify the lapse of the specified time to the CPU  1 . 
     Explained herein is a procedure of transmitting a connection acknowledgement notice frame from the information processing apparatus  17   a  to the information processing apparatus  17   b  when the timer detects the lapse of a specified time in power-off state with reference to a sequence diagram of  FIG. 29 . 
     When the timer  24  detects the lapse of the specified time with the information processing apparatus  17   a  being in the power-off state, the timer  24  issues a power-on request to the power supply controller  9  through the power supply control signal line  23  and reserves a time-out-interrupt to the CPU  1  (step  141 ). This power-on request is received by the power supply switch controller  92  in the power supply controller  9  which sets in the status register  93  a value indicative of a power-on requiring the reproduction of the work state and operates the switch  91  to start supplying electric power onto the power supply line  96  (step  142 ). However, since this is a temporary power-on requested by the timer  24 , the display unit  5  is not supplied with electric power. The CPU  1 , supplied with electric power, starts the reset processing with the program stored in the ROM  6 . After the power-on, the CPU first reads the contents of the status register  93  to recognize the necessity of work state reproduction and starts the work state reproduction processing (step  143 ). When the reproduction of the work state is completed, the CPU  1  informs the power supply controller  9  of the completion of the work state reproduction by writing a particular command into the command register  94  and goes on with the processing from the reproduced work state at the power-off time (step  144 ). The power supply controller  9 , when informed of the completion of the work state preservation processing, notifies this to the timer  24  and starts the timer  95  (step  145 ). The timer  24 , notified of the completion of the work sate reproduction processing, issues the reserved time-out interrupt to the CPU  1  at this time (step  146 ). The CPU  1 , upon receiving the time-out interrupt, requests the network controller  18  to transmit a connection acknowledgement notice frame (step  147 ). The network controller  18 , responsive to the frame transmission request, transmits the connection acknowledgement notice frame to the information processing apparatus  17   b  (step  147 ). Afterward, when the timer  95  started at step  145  expires, this time-out is notified to the power supply switch controller  92  which generates an interrupt to the CPU  1  through the interrupt signal line  22  for requesting the CPU  1  to start processing necessary to turn off the power source (step  148 ). The CPU  1 , upon receiving the interrupt, again starts the work state preservation processing (step  149 ). When the work state preservation processing is completed, the CPU  1  notifies the power supply controller  9  of the completion of the work state preservation by writing a particular command into the command register  94  (step  150 ). This notification is received by the power switch controller  92  in the power supply controller  9  which operates the switch  91  to stop supplying electric power to the respective sections of the information processing Apparatus  17   a  and notifies the second power-off state to the timer  24  (step  151 ). The foregoing processing permits the information processing apparatus  17   a , even in power-off state, to transmit the connection acknowledgement notice frame by again turning on the power source for a temporary time period with a timer interrupt, thereby making it possible to maintain the logical connection with the information processing apparatus  17   b.    
     Next, a tenth embodiment of the present invention will be described with reference to  FIG. 30 . 
       FIG. 30  is a sequence diagram illustrating the processing of the tenth embodiment of the present invention. This sequence diagram represents processing performed by the information processing apparatus  17   a  when receiving a frame from the information processing apparatus  17   b  including a message to be displayed to the user when the information processing apparatus  17   a  remains in power-off state while maintaining the logical connection with the information processing apparatus  17   b.    
     When the network controller  18  receives a frame including a message to be displayed to the user from the information processing apparatus  17   b , the network controller  18 , the power supply controller  9  and the CPU  1  respectively perform a series of processing from step  161  to step  166 . This processing is identical to the processing from step  111  to step  116  shown in the sequence diagram of  FIG. 26 . The CPU  1 , upon receiving a frame reception interrupt from the network controller  18 , starts protocol processing for that frame (step  167 ). In this processing, when the CPU  1  knows that the frame includes a message to be displayed to the user, the CPU  1  writes a particular command into the command register  94  to notify the power supply controller  9  that second power-off is not necessary (step  168 ), and displays the message on the display unit  5  through the display controller  3  (step  169 ). The power supply switch controller  92  in the power supply controller  9 , when receiving this notification, stops the timer  95  started at step  165  and operates the switch  91  to start supplying electric power to the display unit  5  which was not supplied with electric power at step  162  (step  170 ). The foregoing processing permits the information processing apparatus  17   a  to remain in power-off state while maintaining the logical connection with the information processing apparatus  17   b  to display a message to be displayed to the user by automatically turning on again the power source, when receiving such a message. Incidentally, while the tenth embodiment unconditionally displays any received message, the user may be asked before displaying a message at step  169  whether or not the message should be displayed such that the message is displayed only when the user has so instructs. In this case, if no instruction is given within a predetermined time period, that is, if the user is not present in front of the information processing apparatus  17   a , the message is not displayed, the work state is again preserved, and the power supply controller  9  is instructed to turn off the power source.