Patent Publication Number: US-2012047292-A1

Title: Monitoring System, Device Server, Host Computer, Monitoring Method, and Storage Medium

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The disclosure of Japanese Patent Application No. 2010-182828, filed on Aug. 18, 2010, is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to management of peripheral devices connected to a device server. 
     2. Description of the Background Art 
     Device servers for relaying communications between peripheral devices and a host computer have been known to date (for example, Japanese Laid-Open Patent Publication No. 2007-310796). 
     When a device server of this sort is requested by a host computer to acquire peripheral-device pertaining information that the peripheral device retains, if the peripheral device power source is on, the device server acquires the peripheral device information from the peripheral device and reports the information to the host computer. Yet if the peripheral device power source is off, in instances in which the device server still retains peripheral device information it acquired previously when the peripheral device was on, the device server will report the information to the host computer. Consequently, to date there have been situations where the host computer, although able to obtain information on a peripheral device, is yet unable to determine whether the peripheral device is on or off, and thus cannot monitor the operational state of the peripheral device in detail. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve at least a part of the above problems, and to provide a device server and a monitoring system that allow a host computer to monitor the operation state of a peripheral device in more detail. 
     The present invention has been made to solve at least a part of the above problems. The first aspect of the present invention is a monitoring system including a device server and a host computer, the monitoring system for monitoring the operational state of at least one peripheral device connected to the device server. The device server comprises: at least one peripheral device port into which a peripheral device connects; a detection section for detecting whether or not a peripheral device is connected into the peripheral device port; a power supply section for supplying power to a peripheral device via the peripheral device port; and a first control section for controlling start and stop of supply of power from the power supply section to a peripheral device connected to the peripheral device port, and for, from the peripheral device, acquiring and retaining peripheral device information relating to the peripheral device. The host computer comprises: a second control section for instructing the first control section to start or stop supplying power to a peripheral device, for requesting the first control section to notify the second control section of peripheral device information relating to the peripheral device and for acquiring the peripheral device information, and for accessing a peripheral device; and a display unit for displaying the operational state of a peripheral device. The first control section is therein configured to report an online-status notification to the second control section when supply of power is started, and to report an offline-status notification to the second control section when supply of power is stopped. The second control section is configured to detect from receiving an online-status notification that power is being supplied to a peripheral device, detect from receiving an offline-status notification that power is not being supplied to a peripheral device, and display, on the display unit, information based on the acquired peripheral device information, in a display mode that discriminates power being supplied to a peripheral device from power not being supplied thereto. 
     Preferably, the first control section may be further configured so as, in response to the detection section having detected that connection between a peripheral device port and a peripheral device has been broken, to discard information in retains on that peripheral device; and the second control section may be further configured so as to detect, in response to having failed to acquire information on a peripheral device that connection between a peripheral device port and that peripheral device has been broken, and in response to connection between a peripheral device port and a peripheral device having been broken, to stop display on the display unit of information about that peripheral device. 
     Preferably, the first control section may be further configured so as, in response to the second control section having not accessed a peripheral device for a first predetermined period, to stop supply of power from the power supply section to that peripheral device, and report an offline-status notification to the second control section. 
     Preferably, the device server may include a plurality of the peripheral device ports; and the first control section controls start and stop of supply of power with respect to each peripheral device port individually. 
     The second aspect of the present invention is a device server which is connected to a host computer and to at least one peripheral device, the device server comprising: at least one peripheral device port into which a peripheral device connects; a detection section for detecting whether or not a peripheral device is connected to the peripheral device port; a power supply section for supplying power to a peripheral device via the peripheral device port; and a control section for: controlling start and stop of supply of power to a peripheral device; acquiring peripheral device information relating to the peripheral device, from the peripheral device, and retaining the peripheral device information; and notifying the host computer of the peripheral device information in accordance with a request from the host computer. The control section, if the detection section has detected that a peripheral device is connected to the peripheral device port and if the power supply section has started supplying power to the peripheral device, acquires and retains the peripheral device information, and reports online-status notification indicating that power is being supplied to the peripheral device, to the host computer; if the detection section has detected that a peripheral device is connected to the peripheral device port and if the power supply section has stopped supplying power to the peripheral device, reports offline-status notification indicating that power is not being supplied to the peripheral device, to the host computer; and if the detection section has detected that connection between the peripheral device port and a peripheral device has been terminated, discards the retained peripheral device information. 
     The second aspect of the present invention is a host computer which is connected to a device server and monitors the operation state of a peripheral device connected to the device server, the host computer comprising: a control section for acquiring, from the device server, online-status notification, offline-status notification, and peripheral device information relating to a peripheral device connected to the device server; and a display unit for displaying the operational state of a peripheral device. The control section instructs the device server to start or stop supplying power to a peripheral device; detects that supply of power to a peripheral device has been started, based on the online-status notification; detects that supply of power to a peripheral device has been stopped, based on the offline-status notification; and displays, on the display unit, information based on the peripheral device information, in a display mode that discriminates the case where power is being supplied to a peripheral device and the case where power is not being supplied to a peripheral device from each other. 
     The present invention can be implemented in a variety of modes. Besides a monitoring system, a device server, and a host computer, the present invention is also directed to, for example, a method for realizing their functions, and a computer-readable non-transitory storage medium having stored therein a program for realizing their functions. 
     The present invention can provide a device server and a monitoring system that allow a host computer to monitor the operation state of a peripheral device in more detail. 
     The present invention is suitable to, for example, a device server for relaying communication between a peripheral device and a host computer. In addition, the present invention is suitable to, for example, a peripheral device monitoring system including these devices. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the configuration of a peripheral device monitoring system according to an embodiment of the present invention; 
         FIG. 2  is a flowchart showing the operation of the peripheral device monitoring system according to the embodiment of the present invention; 
         FIG. 3  is a state shifting diagram of the operation state of the peripheral device monitoring system according to the embodiment of the present invention; 
         FIG. 4  is a diagram for explaining the operation of the peripheral device monitoring system according to the embodiment of the present invention performed when a peripheral device is connected; 
         FIG. 5  is a diagram for explaining the operation of stopping supply of power to a peripheral device performed by the peripheral device monitoring system according to the embodiment of the present invention; and 
         FIG. 6  is a diagram for explaining the operation of the peripheral device monitoring system according to the embodiment of the present invention performed when a peripheral device is accessed again. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments 
       FIG. 1  is a diagram showing the configuration of a peripheral device monitoring system according to an embodiment of the present invention. The peripheral device monitoring system includes a host computer (HC)  10  and a device server  20 . As an example, in the present embodiment, a hard disk  30  and a TV tuner  40  which are USB devices are connected, as peripheral devices, to the peripheral device monitoring system. In addition, in the present embodiment, the case where the hard disk  30  is monitored will be described as an example. However, a peripheral device to be monitored is not limited thereto. Other than this, a variety of peripheral devices such as a printer and a scanner may be monitored. 
     The host computer  10  and the device server  20  are connected via a LAN cable  50 . The device server  20  and the hard disk  30  are connected via a peripheral device cable  60 . The device server  20  and the TV tuner  40  are connected via a peripheral device cable  61 . In the present embodiment, the peripheral device cables  60  and  61  are USB cables, as an example. The host computer  10  includes a display (display section)  11 , and displays the operation state of the hard disk  30  on the display  11 . 
     The host computer  10  includes a CPU  100  (second control section), a RAM  110 , a ROM  120 , a hard disk (HD)  130 , a LAN port  140 , and an output interface  150 . The hard disk  130  stores a peripheral device management program  131 . The CPU  100  executes the peripheral device management program  131  to control components of the device server  20 , thereby monitoring and managing the operation state of each peripheral device connected to the device server  20 . The display  11  is connected to the output interface  150 . 
     The device server  20  includes a CPU  200  (first control section), a RAM  210 , a ROM  220 , a LAN port  240 , a peripheral device port A 250 , a peripheral device port B 251 , switches  260  and  261 , and a power supply section  270 . The LAN cable  50  is connected to the LAN port  240 , and the host computer  10  and the device server  20  are connected via the LAN cable  50 . The hard disk  30  is connected to the peripheral device port A 250  via the peripheral device cable  60 , and the TV tuner  40  is connected to the peripheral device port B 251  via the peripheral device cable  61 . It is noted that since the peripheral device port A 250  and the peripheral device port B 251  have the same function, the TV tuner  40  may be connected to the peripheral device port A 250 , and the hard disk  30  may be connected to the peripheral device port B 251 . The switch  260  is a detection section for detecting whether or not the peripheral device cable  60  is connected to the peripheral device port A 250 , and the switch  261  is a detection section for detecting whether or not the peripheral device cable  61  is connected to the peripheral device port B 251 . 
     The power supply section  270  controls the supply of bus power to the peripheral device port A 250  and the peripheral device port B 251 , in accordance with an instruction from the CPU  200 . The CPU  200  controls the components of the device server  20 , and if there is a power-off request from the host computer  10  or if a peripheral device has not been accessed (control of a peripheral device or input/output of data to a peripheral device has not been performed) for a first predetermined period, the CPU  200  stops supplying bus power to the peripheral device port A 250  and the peripheral device port B 251 . It is noted that the CPU  200  controls each of the supply of bus power to the peripheral device port A 250  and the supply of bus power to the peripheral device port B 251  separately. For example, the CPU  200  can supply bus power to the peripheral device port A 250  while stopping supplying bus power to the peripheral device port B 251 . 
       FIG. 2  is a flowchart showing the operation of the peripheral device monitoring system. Processing shown in this flowchart is executed for each of peripheral devices connected to the peripheral device ports separately, after step S 200 . There are five operation states of the peripheral device monitoring system, that is, a start state, a no-device state, a power-off state, an available state, and an in-use state, which correspond to the respective operation states of each peripheral device. Hereinafter, processing in each state will be described. 
     First, in step S 200  in the start state, the host computer  10  and the device server  20  are booted up (step S 200 ). Specifically, power switches (not shown) of the host computer  10  and the device server  20  are turned on by a user, whereby the host computer  10  and the device server  20  are booted up. At this point of time, the host computer  10  and the device server  20  have become communicable to each other via the LAN cable  50 . If the CPU  100  of the host computer  10  has detected that the device server  20  has been booted up, the CPU  100  loads the peripheral device management program  131  from the hard disk  130  and executes the peripheral device management program  131 , to start monitoring and managing the peripheral device. It is noted that the CPU  100  can execute the peripheral device management program  131  in accordance with an instruction from the user, irrespective of whether or not the device server  20  has been booted up. 
     In step S 202 , the CPU  200  of the device server  20  determines whether or not the peripheral device cable  60  has been connected to the peripheral device port A 250 . If the peripheral device cable  60  has been connected (YES in step S 202 ), the CPU  200  of the device server  20  shifts processing to step S 230 . The CPU  200  can easily determine whether or not the peripheral device cable  60  has been connected to the peripheral device port A 250 , based on the state of the switch  260 . The CPU  200  notifies the host computer  10  of information indicating whether or not the peripheral device cable  60  has been connected. In step S 230 , the corresponding peripheral device has become able to be accessed. If the peripheral device cable  60  is not connected (NO in step S 202 ), the CPU  200  repeatedly executes the process of step S 202 , waiting for connection. When the peripheral device cable  60  is not connected to the peripheral device port A 250 , there is no peripheral device to be monitored. 
     When the operation state of the peripheral device monitoring system has shifted to the available state, the peripheral device monitoring system operates as follows. In step S 230 , the CPU  200  of the device server  20  boots up the hard disk  30  which is a peripheral device. As described later, step S 230  includes: a power supply start process for starting supply of power to the hard disk  30  by supplying bus power to the peripheral device port A 250 ; a mounting process for making a file in the hard disk  30  readable and writable (accessible) by the host computer  10 ; and an online-status notification reporting process for reporting, to the host computer  10 , online-status notification indicating that the hard disk  30  has become accessible from the host computer  10  and has gone online to the device server  20 . In addition, in step S 230 , the CPU  200  obtains peripheral device information from the hard disk  30 . The peripheral device information is retained by the device server  20 . In addition, in accordance with a request from the host computer  10 , the peripheral device information retained by the device server  20  is sent from the device server  20  to the host computer  10 . The host computer  10  obtains the peripheral device information as needed, and uses the obtained peripheral device information for monitoring/management, or access. If the hard disk  30  has gone online to the device server  20 , the CPU  200  of the device server  20  becomes able to obtain the peripheral device information from the hard disk  30 . 
     In step S 234 , if the CPU  100  of the host computer  10  is to access the hard disk  30  (YES in step S 234 ), the CPU  100  shifts processing to step S 242  and shifts the operation state of the peripheral device monitoring system to the in-use state. On the other hand, if the CPU  100  is not to access the hard disk  30  (NO in step S 234 ), the CPU  100  shifts processing to step S 236 . Here, whether or not the CPU  100  of the host computer  10  is to access the hard disk  30  is determined by, for example, whether or not it is necessary to read or write a file in the hard disk  30  immediately. 
     In step S 236 , if the host computer  10  has made a power-off request for the hard disk  30  which is an instruction to stop supplying power to the hard disk  30 , or if the first predetermined period T 1  has passed since the process of step S 230  was executed or since the latest return if the operation state of the peripheral device monitoring system returned from the in-use state (YES in step S 236 ), the CPU  200  shifts processing to step S 220  and shifts the operation state of the peripheral device monitoring system to the power-off state. In this way, it becomes possible to stop supplying power to a peripheral device that has not been accessed for the first predetermined period T 1 , even without a power-off request from the host computer  10 . On the other hand, if there is not a power-off request for the hard disk  30  and the first predetermined period T 1  has not passed (NO in step S 236 ), the CPU  200  shifts processing to step S 238 . 
     In step S 238 , the CPU  200  determines whether or not the peripheral device cable  60  is connected to the peripheral device port A 250 . The CPU  200  can easily determine this by monitoring the state of the switch  260 . If the peripheral device cable  60  is detached from the peripheral device port A 250  (NO in step S 238 ), the CPU  200  shifts processing to step S 212  and shifts the operation state of the peripheral device monitoring system to the no-device state. On the other hand, if the peripheral device cable  60  is not detached from the peripheral device port A 250  (YES in step S 238 ), the CPU  200  shifts processing to step S 234  to repeat the processes of the foregoing steps (steps S 234  to S 238 ). 
     Next, the case where the operation state of the peripheral device monitoring system is the in-use state will be described. In step S 242 , the host computer  10  becomes able to access the hard disk  30 . Specifically, the CPU  100  of the host computer  10  installs a piece of software (a driver) for accessing the hard disk  30 . As a result, the host computer  10  has become able to access the hard disk  30 , whereby the host computer  10  has become able to read and write a file in the hard disk  30 . In step S 244 , the CPU  100  determines whether or not there is a disconnection request from the host computer  10 . If there is a disconnection request from the host computer  10  (YES in step S 244 ), the CPU  100  shifts processing to step S 234 , and the operation state of the peripheral device monitoring system returns to the available state. A disconnection request is generated when the access from the host computer  10  to the hard disk  30  has been finished. If there is not a disconnection request (NO in step S 244 ), the CPU  200  determines whether or not a second predetermined period T 2  has passed since the process of step S 242  was executed, in step S 246 . If the second predetermined period T 2  has passed (YES in step S 246 ), the CPU  200  shifts processing to step S 234 , and shifts the operation state of the peripheral device monitoring system to the available state. It is noted that if the host computer  10  has accessed the hard disk  30  before the second predetermined period T 2  passes, the count of the elapsed time for the second predetermined period T 2  is reset and another count is started. In this way, it becomes possible to shift the operation state of the peripheral device monitoring system to the power-off state after shifting the operation state to the available state, even if the host computer  10  has not accessed the hard disk  30  or has not made a disconnection request for the hard disk  30  for the second predetermined period T 2 . In addition, if the hard disk  30  is successively accessed, the in-use state can be kept. If the second predetermined period T 2  has not passed (NO in step S 246 ), the CPU  200  shifts processing to step S 244  to repeat the processes of steps S 244  and S 246 . 
     Next, the case where the operation state of the peripheral device monitoring system is the power-off state will be described. In step S 220 , the CPU  200  unmounts the hard disk  30 . As a result, the host computer  10  becomes unable to access the hard disk  30  though the hard disk  30  is connected to the device server  20  in a physical sense. Next, in step S 222 , the CPU  200  controls the power supply section  270  to stop supplying power to the hard disk  30 . In step S 224 , the CPU  200  reports offline-status notification to the host computer  10 . In this way, the CPU  200  notifies the host computer  10  that the hard disk  30  has gone offline. In addition, if, for the first predetermined period T 1 , the host computer  10  has not accessed the hard disk  30  or made a power-off request for the hard disk  30 , and the peripheral device cable  60  has not been detached, the CPU  200  of the device server  20  stops supplying power to the hard disk  30  to make the hard disk  30  offline. Thereafter, the CPU  200  of the device server reports offline-status notification to the host computer  10 . In this way, the CPU  200  can notify the host computer  10  that the CPU  200  has stopped supplying power to the hard disk  30 . 
     In step S 226 , the CPU  200  waits for the host computer  10  to make a power-on request for the hard disk  30 , that is, an instruction to start supplying power to the hard disk  30 . If the host computer  10  has made a power-on request, that is, an instruction to start supplying power to the hard disk  30  (YES in step S 226 ), the CPU  200  shifts processing to step S 230  and shifts the operation state of the peripheral device monitoring system to the available state. 
     Next, the case where the operation state of the peripheral device monitoring system is the no-device state will be described. In step S 210 , the peripheral device information about the hard disk  30  retained by the device server  20  is changed from the state in which the hard disk  30  is connected to the device server  20 , to the state in which the hard disk  30  is not connected to the device server  20  (the state in which there is no device). In step S 212 , whether or not a third predetermined period T 3  has passed since the process of step S 210  was executed. If the third predetermined period T 3  has passed (YES in step S 212 ), the CPU  200  determines that connection between the hard disk  30  and the device server  20  has been terminated, executes an unmounting process (step S 215 ), and stops supplying power (step S 216 ). In the case where mounting process has not been performed, the process of step S 215  is skipped. In the case where supply of power has not been started, the processes of steps S 215  and S 216  are skipped. This is the same as in the processes of steps S 220  and S 222 . In addition, the CPU  200  discards the peripheral device information (step S 217 ), shifts processing to step S 202 , and shifts the operation state of the peripheral device monitoring system to the start state. At this time, the host computer  10  fails to obtain the peripheral device information when the host computer  10  attempts to obtain the peripheral device information because the peripheral device information has been discarded, thereby detecting that the peripheral device cable has been detached from the peripheral device port. On the other hand, if the third predetermined period T 3  has not passed (NO in step S 212 ), the CPU  200  determines again whether or not the peripheral device cable  60  has been connected to the peripheral device port A 250 , in step S 214 . If the peripheral device cable  60  has been connected to the peripheral device port A 250  (YES in step S 214 ), the CPU  200  shifts processing to step S 230 , and shifts the operation state of the peripheral device monitoring system to the available state. It is noted that, in this case, since supply of power and mounting processes have been performed, among steps S 231  to S 233  described later which are included in step S 230 , steps S 231  and S 232  are skipped, while, in step S 233 , the peripheral device information is obtained (again) and the online-status notification is sent. On the other hand, if the peripheral device cable  60  is not connected to the peripheral device port A 250  (NO in step S 214 ), the CPU  200  shifts processing to step S 212 . Thereafter, the CPU  200  waits for the third predetermined period T 3  to pass, repeating the processes of steps S 212  and S 214 . While the CPU  200  is waiting, the unmounting process is not performed and supply of power to the hard disk  30  is not stopped. As a result, even if the peripheral device cable  60  is detached from the peripheral device port A 250 , if the peripheral device cable  60  is connected again within a certain period, the host computer  10  immediately becomes able to access the peripheral device. As a result, it becomes unnecessary to perform the power supply start process and the mounting process every time, for example, the peripheral device cable  60  is temporarily detached from the peripheral device port A 250  owing to contact failure. In addition, when the CPU  200  is waiting, the peripheral device information includes information indicating that the hard disk  30  is not connected to the device server  20 . The host computer  10  can detect that the host computer  10  cannot currently access the hard disk  30 , by obtaining the peripheral device information. 
       FIG. 3  is a state shifting diagram of the operation state of the peripheral device monitoring system. Operation states for the peripheral device monitoring system can be shifted to each other via the available state, as shown in  FIG. 3 . 
     For example, shifting from the start state to the available state is performed in the case where the result of step S 202  in  FIG. 2  is YES, that is, in the case where the peripheral device cable  60  connected to a peripheral device desired to be used has been connected to the peripheral device port A 250  ( FIG. 1 ) of the device server  20 . It is noted that the available state cannot be directly shifted to the start state. 
     Shifting from the available state to the in-use state is performed in the case where the result of step S 234  in  FIG. 2  is YES, that is, in the case where the host computer  10  is to access a peripheral device. On the contrary, shifting from the in-use state to the available state is performed in the case where the result of step S 244  in  FIG. 2  is YES, that is, there is a disconnection request from the host computer  10  ( FIG. 1 ); or in the case where the result of step S 246  is YES, that is, the host computer  10  has not access the hard disk  30  or sent a disconnection request to the hard disk  30  for the second predetermined period T 2 . 
     Shifting from the available state to the power-off state is performed in the case where the host computer  10  ( FIG. 1 ) has sent a power-off request (YES in step S 236 ) before the second predetermined period T 1  passes, or in the case where, for the first predetermined period T 1 , the host computer  10  has not accessed the hard disk  30  (NO in step S 234 ) and the peripheral device cable  60  has not been detached (YES in step S 238 ). On the other hand, shifting form the power-off state to the available state is performed in the case where the result of step S 226  in  FIG. 2  is YES, that is, there is a power-on request from the host computer  10 . 
     Shifting from the available state to the no-device state is performed in the case where the result of the step S 238  in  FIG. 2  is NO, that is, the peripheral device cable  60  is detached from the peripheral device port A 250  ( FIG. 1 ). On the other hand, shifting from the no-device state to the available state is performed in the case where the result of step S 214  in  FIG. 2  is YES, that is, the peripheral device cable  60  has been connected to the peripheral device port A 250 . 
     Shifting from the no-device state to the start state is performed in the case where the result of step S 212  in  FIG. 2  is YES, that is, the third predetermined period T 3  has passed while the peripheral device cable  60  is not connected. It is noted that the start state cannot be shifted to the no-device state. 
       FIG. 4  is a diagram for explaining the operations of the device server  20  and the host computer  10  performed from when a peripheral device cable is connected until the corresponding peripheral device becomes accessible. (A) of  FIG. 4  shows an example of a management screen displayed on the display  11  of the host computer  10 , and (B) of  FIG. 4  shows a flowchart of steps S 230  to S 243  which is included in the flowchart in  FIG. 2 . The process of step S 230  will be described in detail, being divided into steps S 231  to S 233 . Here, it will be assumed that the TV tuner  40  has been already connected to the peripheral device port B 251 , power being supplied to the TV tuner  40 , and then the hard disk  30  is to be newly connected to the peripheral device port A 250 . In addition, in the flowchart, the process steps performed by the host computer  10  and the process steps performed by the device server  20  are indicated separately. Before the peripheral device cable  60  of the hard disk  30  is connected to the peripheral device port A 250 , only the TV tuner  40  is connected to the peripheral device port B 251 . Therefore, the CPU  100  of the host computer  10  has obtained only peripheral device information about the TV tuner  40 , and as shown in (A) of  FIG. 4 , displays, on the management screen of the display  11 , only “Device B” which indicates the TV tuner  40 , for example. 
     In step S 231 , the CPU  200  of the device server  20  instructs the power supply section  270  to supply power to the hard disk  30 . In step S 232 , the CPU  200  executes the mounting process for the hard disk  30 . Then, in step S 233 , the CPU  200  reports online-status notification indicating that the hard disk  30  has gone online, to the host computer  10 , and obtains peripheral device information from the hard disk  30 . By these process steps, booting up of the hard disk  30  (peripheral device) is completed. 
     Here, the host computer  10  receives the online-status notification and immediately accesses the hard disk  30  (YES in step S 234 ). In step S 242 , the CPU  100  of the host computer  10  installs a piece of software (a driver) for accessing the hard disk  30 . As a result, the host computer  10  has become able to access the hard disk  30 . As shown (A) of  FIG. 4 , when the CPU  100  of the host computer  10  has received the online-status notification, the CPU  100  displays, on the management screen of the display  11 , “Device A” which indicates the hard disk  30  in addition to “Device B” which indicates the TV tuner  40 , for example. 
       FIG. 5  is a diagram for explaining the operations of the device server  20  and the host computer  10  performed from when a power-off request for peripheral device is performed until supply of power is actually stopped. (A) of  FIG. 5  shows an example of a management screen displayed on the display  11  of the host computer  10 , and (B) of  FIG. 5  shows a flowchart of steps S 236  to S 224  which is included in the flowchart in  FIG. 2 . Here, it will be assumed that the hard disk  30  has been already connected to the peripheral device port A 250  and the TV tuner  40  has been already connected to the peripheral device port B 251 , power being supplied to both of them, and then the hard disk  30  is to be powered off. First, the host computer  10  transmits a power-off request to the device server  20 , and the device server  20  receives the power-off request, whereby the result of the determination in step S 236  becomes YES, and processing shifts to step S 220 . In step S 220 , the CPU  200  executes the unmounting process for the hard disk  30 , and in step S 222 , the CPU  200  stops supplying power to the hard disk  30 . In step S 224 , the CPU  200  reports, to the host computer  10 , offline-status notification indicating that supply of power to the hard disk  30  has been stopped and the hard disk  30  has gone offline. It is noted that even if there is no power-off request from the host computer  10 , if, for the first predetermined period T 1 , the host computer  10  has not accessed the hard disk  30  and the peripheral device cable  60  has not been detached, the CPU  200  executes the above processes. 
     If the host computer  10  has received the offline-status notification, the CPU  100  of the host computer  10  changes the content displayed on the display  11 . For example, as shown in (A) of  FIG. 5 , “Device A”, which indicates the hard disk  30 , displayed in black is to be displayed in gray. By display in gray, it is possible to notify the user that the hard disk  30  is connected to the device server  20  but the hard disk  30  is powered off. That is, in the present embodiment, by changing the indication of each peripheral device displayed on the management screen, it becomes possible to notify the user whether the peripheral device is ON or OFF. It is noted that if the peripheral device cable  60  is detached from the peripheral device port A 250 , the peripheral device information about the hard disk  30  is discarded, and the host computer  10  detects that the device server  20  no longer retains the peripheral device information. Based on the detection, for example, the indication of “Device A” itself, which indicates the hard disk  30 , is stopped. 
       FIG. 6  is a diagram for explaining the operations of the device server  20  and the host computer  10  performed when a peripheral device is accessed again. Accessing again means that after a peripheral device has been once accessed and then supply of power to the peripheral device is stopped, power is to be supplied to the peripheral device again and the peripheral device is to be accessed again. (A) of  FIG. 6  shows an example of a management screen displayed on the display  11  of the host computer  10 , and (B) of  FIG. 6  shows a flowchart of steps S 226  to S 243  which is included in the flowchart in  FIG. 2 . Here, it will be assumed that the TV tuner  40  has been already connected to the peripheral device port B 251 , power being supplied to the TV tuner  40 ; the hard disk  30  has been already connected to the peripheral device port A 250 , power not being supplied to the hard disk  30 ; the hard disk  30  is to be accessed again. The CPU  100  of the host computer  10  transmits a power-on request for the hard disk  30  to the device server  20 , whereby the result of step S 226  becomes YES. The processes of steps S 231  to S 233  are performed as previously described, and therefore the description thereof is omitted. Here, the process of step S 242  will be described in detail, being divided into steps S 242 - 1  and S 242 - 2 . In step S 241 - 1 , the CPU  100  of the host computer  10  confirms whether or not a piece of software (a driver) for accessing the hard disk  30  has been installed. Normally, in the case of accessing the hard disk  30  again, the piece of software (driver) for accessing the hard disk  30  has been already installed. In this case (YES in step S 242 - 1 ), the hard disk  30  immediately becomes accessible. However, if the driver has been uninstalled for some reason (NO in step S 242 - 1 ), the CPU  100  of the host computer  10  installs the driver (again) in step S 242 - 2 , and then the hard disk  30  becomes accessible. As a result, the host computer  10  can read and write a file in the hard disk  30 . The CPU  100  of the host computer  100  receives online-status notification, and as shown in (A) of  FIG. 6 , changes the color of the indication of “Device A”, which indicates the hard disk  30 , from gray to a normal color (original color, black), for example. 
     In this way, when a peripheral device is connected, the CPU  100  of the host computer  10  displays information about the peripheral device on the display  11  such that the case where power is being supplied to the peripheral device and the case where power is not being supplied to the peripheral device are discriminated from each other, whereby the host computer  10  can monitor the connection states of peripheral devices in more detail. In addition, for example, in the case where the specific name of each peripheral device is included in the corresponding peripheral device information, the host computer  10  may display the specific name such as “hard disk” or “TV tuner” based on the peripheral device information, instead of “Device A”. 
     In the present embodiment, monitoring and management for the hard disk  30  have been described as an example. However, in the present invention, a target of monitoring and management may be the TV tuner  40 , or may be any peripheral device as long as the peripheral device is connected to the device server  20 . Even in such cases, the operation state can be monitored in detail. 
     In addition, in the present embodiment, when a peripheral device cable is detached from a peripheral device port in the available state (NO in step S 238 ), the operation state of the peripheral device monitoring system shifts to the no-device state. However, in any operation state, it is assumed that a peripheral device cable might be detached from a peripheral device port inadvertently. Also in such cases, the operation state may shift to the no-device state to execute the processes of steps S 212  to S 217 , and then processing may shift to step S 202 . It is noted that, at this time, if the mounting process has not been performed, step S 215  is skipped, and if supply of power has not been started, steps S 215  and S 216  are skipped. In addition, steps S 210  to S 214  may be skipped. 
     In the present embodiment, the case where peripheral devices are connected based on USB standard has been described as an example. However, the standard for connection between the device server and peripheral devices is not limited to USB standard. Another standard such as IEEE 1394 standard may be employed. 
     In the present embodiment, whether or not the peripheral device cable  60  is connected to the peripheral device port A 250 , and whether or not the peripheral device cable  61  is connected to the peripheral device port B 251  are detected by the switches  260  and  261 , respectively. However, a detection device other than a switch, for example, a sensor may be used. In addition, the device server may include any number of peripheral device ports, and any number of peripheral device may be monitored and managed by the peripheral device monitoring system. 
     In the present embodiment, when the peripheral device cable  60  is not connected to the peripheral device port A 250 , information about the hard disk  30  (peripheral device) is not displayed. On the other hand, when the peripheral device cable  60  is connected to the peripheral device port A 250 , if power is being supplied to the hard disk  30 , information about the hard disk  30  is displayed in black, and if power is not being supplied to the hard disk  30 , information about the hard disk  30  is displayed in gray, whereby the two cases are discriminated. However, the method for discrimination is not limited thereto, and various display manners may be employed. The indication of a peripheral device to which power is not being supplied may be displayed with a mark such as “x”, or the indication of a peripheral device to which power is being supplied may be displayed with a flag. 
     While the embodiments of the invention have been described in detail, the foregoing description of the embodiments of the invention is examples for facilitating the understanding of the invention, and does not limit the invention. It will be understood that numerous other modifications and variations can be devised without departing from the intention of the invention, and from the scope of claim of the invention, and that the equivalents for the invention are included.