Abstract:
The present invention relates to a power management apparatus and method. Many organisations have reached an agreement with the power companies to reduce their power consumption during periods of relatively high demand. Reducing the power consumption often entails temporarily switching off air conditioning or heating or reducing the effectiveness of them. However, in some circumstances, these measures are insufficient. Therefore, the present invention is arranged to reduce the power consumption state of, for example, computers. A server transmits to each computer a network message which instructions those computers that have already entered a reduced power consumption state to adopt a different power consumption state, which has a power consumption that is less than their existing power consumption state. Since the computers that are addressed are already in a reduced power consumption state, it is very likely that the users of those machines have not used them for some time and may be away from their desk. Therefore, providing the computers are restored to their original state before the user returns or needs to use the computer, they will be oblivious to their machine having been placed in the different power consumption state. This has the advantage of allowing an organisation to meet its contractual commitments without greatly inconveniencing the users.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a power management method and apparatus.  
         BACKGROUND TO THE INVENTION  
         [0002]    It will be appreciated that large commercial organisations consume significant amounts of energy. In particular, these organisations consume a significant amount of electrical energy for heating, lighting etc. Often such organisations have an agreement with their energy supplier to reduce power consumption during periods of unusually high demand by, for example, switching off or reducing the effectiveness of the heating or air-conditioning. However, in instances of particularly high demand, even these measures may be insufficient to enable the organisation to comply with the agreement.  
           [0003]    It is an object of the present invention at least to mitigate some of the problems of the prior art.  
         SUMMARY OF INVENTION  
         [0004]    Accordingly, a first aspect of the present invention provides a method of operating an apparatus having a system context and comprising a power management system for placing the apparatus in at least one of first and second power states of a plurality of power states; the apparatus being arranged to consume less power in the second power state than in the first power state, and a communication device via which command data can be received from a remote device; the method comprising the steps of  
           [0005]    entering the first power state in which the communication device remains operable and at least a portion of the system context is maintained; the step of entering including outputting data representing the system context for storage on a non-volatile storage medium;  
           [0006]    receiving, via the communication device, first command data instructing the power management system to place the apparatus in die second power state; and  
           [0007]    entering the second power state.  
           [0008]    By exploiting power saving features of ACPI compliant devices, a power saving policy can be implemented by an organisation that does not inconvenience their employees greatly.  
           [0009]    This follows from the fact that the client machines that are arranged to operate in a reduced power state are those machines that are Dot currently being used by the users. The user&#39;s machine is made available to the power management system when that machine has entered a power saving state. The unused machine is arranged to adopt a further power saving state in which even less power is consumed.  
           [0010]    It is generally prudent to reduce, preferably to a minimum, any inconvenience to the users of client machines within an organisation. Therefore, embodiments provide a method, filter comprising the steps of  
           [0011]    receiving, from the remote device, second command data for instructing the power management system to place the apparatus in a power state other tan the second power state;  
           [0012]    adopting, in response to receiving the second command data, a power state other than the second power state; and  
           [0013]    restoring the system context using the data representing the system context previously output for storage on the non-volatile storage medium.  
           [0014]    Preferred embodiments provide a method in which the step of adopting a power state other than the second power state comprises the step of adopting the first power state. Preferably, the first power state is a safe S3/quick S4 state.  
           [0015]    It is desirable to provide some mechanism to allow the user to place the computer in a particular power management state. Suitably, embodiments provide a method in which the step of entering the first power state is responsive to receipt or generation of an event Preferably, the event is one of a user, computer or a communication device generated event.  
           [0016]    Preferred embodiments provide a method in which the step of leaving the second power state comprises the step of adopting a non-power saving state.  
           [0017]    A second aspect of the present invention provide an apparatus capable of having a system context and comprising a power management system for placing the apparatus in at least one of first and second power states of a plurality of power states; the apparatus being arranged to consume less power in the second power state than in the fist power state, and a communication device via which command data can be received from a remote device; the apparatus further comprising  
           [0018]    means to enter the first power state in which the communication device remains operable and at least a portion of the system context is maintained; including means to output data representing the system context for storage on a non-volatile storage medium;  
           [0019]    means to receive, via the communication device, first command data instructing the power management system to place the apparatus in the second power state; and  
           [0020]    means to place the apparatus in the second power state, 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:  
         [0022]    [0022]FIG. 1 illustrates a power management environment according to an embodiment of the present invention;  
         [0023]    [0023]FIG. 2 shows mi greater detail a client machine and a power management server of the power management environment for implementing an embodiment of the present invention;  
         [0024]    [0024]FIG. 3 depicts flowcharts of the processing undertaken by a client machine and a server according to an embodiment in preparation for implementing a power management policy;  
         [0025]    [0025]FIG. 4 illustrates further flowcharts of the processing performed by a client machine and a server according to an embodiment upon expiry of a period of organisational power management;  
         [0026]    [0026]FIG. 5 illustrates flowcharts of the processing performed to support a user instigated wake-up for an embodiment;  
         [0027]    [0027]FIG. 6 illustrates schematically prior an ACPI power management states and sate transitions; and  
         [0028]    [0028]FIG. 7 depicts the power states and states transitions for client machines according to preferred embodiments. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring to FIG. 1, there is shown a power management environment  100  of an organisation. The power management environment  100  comprises a power management server  102 , which runs a power management application  104 . The power management application  104  is arranged to control the power consumption of a number of client machines  106 ,  108  and  110 . The power management application  104  communicates with each of the client machines  106  to  110  via a network  112 . Each client machine has an associated system context  114  to  118 . A system context is used by operating system directed power management software, described with reference to FIG. 2, to manage the power consumption of a corresponding client machine. The client machines  106  to  110  are arranged, under the control of the operating system directed power management software, to enter one of a number of power management states. The power management states may include a working state, having the highest power consumption, and a hibernate state, having the lowest power consumption. There are further, graduated, power management states between the working state and the hibernate state. Each power management state has an associated degree of power consumption and system context. The preferred power management states of embodiments are described in greater detail with reference to FIG. 7.  
         [0030]    When a client machine is about to enter one of the power management states, that client machine transmits a message  124  to  128  to the power management application  104 .  
         [0031]    The message  124  to  128  informs the power management application  104  of the entry of the corresponding client machine into a power management state. Preferably, the message contains an indication of the power management state adopted by the client machine. The message also contains client machine identification data for identifying the client machine to the power management application  104 . Preferably, the power management state reported by the message is a state other than the working state, but may include the worldling state.  
         [0032]    In preferred embodiments, the client machines  106  to  110  report to the power management server  102  upon entry into a safe S3/quick S4 state, which is described in greater detail with reference to FIG. 7.  
         [0033]    The power management server  102  has an associated HDD  120  for storing power state data  122  identifying which, if any, of the client machines have entered one of the reduced power consumption states of the power management states. In preferred embodiments, the power state data  122  is derived from the messages  124  to  128  transmitted by those client machines  106  to  110  that have adopted a power management state other than the working state.  
         [0034]    Prior to entering a period for which the organisation has agreed to reduce power consumption, the power management application  104  retrieves the power state data  122  from the HDD  120  and transmits a network message  130  to each of the client machines identified by that data. The network message  130  contains data that instructs the identified client machines to adopt a different power management state. It will be appreciated that the client machines will already be in a reduced power consumption state. Therefore, in preferred embodiments, the network message data instructs the client machines  106  to  110  to enter a power management state having a lower power consumption than a current power management state. In preferred embodiments, the lower power consumption state, or second power state, corresponds to the hibernate or S4 state.  
         [0035]    The client machines, when in power management states other than the working state, can still receive and respond to network messages. Therefore, once the period of time for which an organisation has agreed to reduce power consumption has passed, the power management application  104  broadcasts to each, or a portion, of the client machines, a wake-up network message The wake-up network message contains data instructing the client machines  106  to  110  to restore their previous power management state. Alternatively, or additionally, the client machines may be instructed to enter a predetermined power management state or to enter a state that is prescribed by the network message.  
         [0036]    The system context of a client machine is saved prior to entering a power saving state. The system context is used to allow the client machines  106  to  110  to be placed in a power saving state. Upon detection of a wake-up event, a wake-up process is instigated in which the system context is restored and the client machine is arranged to adopt another power management state. The other state is usually the working state.  
         [0037]    [0037]FIG. 2 illustrates in greater detail a selected client machine and power management server arrangement  200  The arrangement  200  shows one of the client machines, that is, client machine  106 , which has a processor  202  and RAM  206  containing a RAM image  208 . In general, the client machines  106  to  110  use ACPI specification power management Therefore, the client machine  106  also comprises a BIOS  210 , which supports ACPI routines The client machine  106  has an operating system  212 , which is arranged to implement operating system directed power management (OSPM) using associated OSPM software  214 .  
         [0038]    The client machine  106  transmits and receives network messages via a network card  225 . The client machine  106  may run various applications  216  and  218 . Additional hardware and software functionality is provided m the form of power management event detection logic  220 , which detects events in response to which the current power management state of the client machine  106  may be changed to another power management state. For example, the user may depress an ON/OFF button  224 , in response to which the client machine  106  may effect a transition from a current sleeping state to a working state. Alternatively, the ON/OFF button  224  may be used to instigate a software shutdown of the client machine  106 . To effect a software shutdown, the client machine  106  should adopt a reduced power consumption state of the power management states.  
         [0039]    As described above, a particular event to which the client machines are arranged to respond is a network-generated event, which signals to the OSPM software  214  that data is being received and the network card  225  and the RAM should be suitably powered-up to allow reception of the data.  
         [0040]    The power management event detection logic  220  is used to cause wake-up and sleep logic  222 , in conjunction with the OSPM software  214 , to restore the system context and to place the client machine  106  in one of the power management states. The system context is stored on a locally accessible HDD  226  during adoption of a reduced power consumption state.  
         [0041]    Although this embodiment uses a network card  225 , it will be appreciated that other embodiments may use some other communication device for communicating with the server. For example, a wireless LAN may be used to communicate with the server The wireless LAN will have a transceiver as opposed to a network card. Alternatively, or additionally, a modem may be used to support network message exchanges. Still further, the device for receiving the command to enter a power saving mode of operation may be connected to the client machine via a USB connection. For example, AUSB may be used to listen for power alerts that have been broadcast using conventional radio frequencies in a manner that is similar to RDS being transmitted over conventional music radio channels. Still farther, the command to enter a power saving mode of operation may be transmitted to the client machine by modulation of the power supply or by superimposing a signal on the power supply signal. In this manner, the device for listening for the command to enter a reduced power consumption state may be incorporated into the client machine.  
         [0042]    The current power management state of a client machine is stored within an ACPI storage area  210 ′. The previous power management state is stored within an ACPI storage area  210 ″. The previous power management stale can be used, in the absence of the network message  130  containing an indication of the power management state to be adopted, as a default power management state to be entered by the client machine in response to receiving the network message  130 .  
         [0043]    The server  102  preferably uses a power management schedule  228  to control the timing of the implementation of the organisation&#39;s power management policy. The schedule  228  contains preferred times, Time 1  to Time N , at which the client machines identified by the power state data  122  should adopt a low power consumption state.  
         [0044]    Preferably, since a client machine can enter any one of a number of possible power management states, the power management schedule  228  also contains an indication of the power management states, PS 1  to PS N , that should be adopted by the client machines.  
         [0045]    It will be appreciated that the first time, Time 1 , may represent a time at which all addressed client machines should adopt a lower power management state. The second time, Time 2 , may represent a time at which the addressed client machines can revert back to their original power management state or can adopt a higher power management state prescribed by the corresponding power state, PS 2 .  
         [0046]    In some embodiments, the absence of a prescribed power management state may be interpreted by the client machines as an instruction to adopt a previous power management state, as determined from the data contained within the ACPI storage areas, the highest power management state or the lowest power management state or to change, in a relative direction, by a predetermined number of the lower management states.  
         [0047]    In some circumstances, the power management application  104  may instruct the client machines to leave a current working state and to adopt one of the lower power management states.  
         [0048]    Referring to FIG. 3, there is shown schematically a pair of flowcharts  300  for operating the power management environment  100  according to an embodiment. A determination is made at step  302  as to whether a power management state other than the current state should be adopted by the client machine  106 . The current state is usually the working state. The decision may be based on a period of user inactivity or an event for forcing a change to another power management state. If the determination is positive, the client machine saves the current system context to the HDD  226  at step  304  and updates the current and previous power management state data in the associated storage areas  210 ′ and  210 ″.  
         [0049]    A message is transmitted, at step  306 , to the power management server  102  that the client machine  106  about to enter a power saving state. The message also contains data identifying the client machine. At step  308 , the client machine, having transmitted the network message, enters a prescribed power management state. In preferred embodiments, the prescribed power management state is the safe S3/quick S4 state, which is described hereafter. It will be appreciated that the network card  225  and the power management event detection logic  220  are still responsive to network events during this state.  
         [0050]    The powers management server  102 , at step  310  receives the network message. The power management server, at step  312 , adds to the power state data  122 , representing those machines that have entered a stand-by state, the client machine identification data contained within the received network message. A determination is made at step  314  as to whether or not it is time to implement the organisation&#39;s lower management policy. It will be appreciated that rather than this step having an then format., a more practical realisation would use some form Of timed interrupt process which causes the power management server  102  to instigate implementation of the power management policy in response to that interrupt process. If the determination at step  314  is negative, control is returned to step  310 . If the determination is positive, the power management application  104 , at step  316 , retrieves the data  122  representing those client machines that have adopted a reduced power management state and transmits, at step  318 , the network message  130  to instruct the client machines to enter an even lower power consumption state. Preferably, as indicated above, the even lower power consumption state is the S4 hibernate state.  
         [0051]    The network message  130  may contain an indication of the lower power consumption state to be adopted or may instruct the client machines to adopt the next lowest power consumption state. It will be appreciated that the latter encompasses a transition from a working state to a safe S3/quick S4 state or from a safe S3/quick S4 state to the S4 or hibernate state.  
         [0052]    Since the user&#39;s machine is unused in tile safe S3/quick S4 state, that is, it is in a state other than the working state, the user, at the time of the implementation of the power management policy, will be unaware that their client machine has changed its power consumption state.  
         [0053]    [0053]FIG. 4 slows a pair of flowcharts  400  for restoring the power management states of the client machines following expiry of the organisation&#39;s period of power management. At step  402 , the power management application  104  determines that the power management period gas expired. In response to that determination, at step  404 , the power management application  104  transmits a wake-up network message to all of the client machines that were previously instructed to adopt a lower power consumption state. As indicated above, even in reduced power consumption states, the network card  225  and the power management event detection logic  220  are operable to detect and respond to network generated events.  
         [0054]    At step  406 , a client machine receives the wake-up network message, which causes the client machine to recover from an existing power management state to a previous or a specified power management state. The client machine is arranged, by the OSPM software,  214 , to assume an appropriate power management state at step  408 .  
         [0055]    If the embodiments are arranged to adopt a previous power management state, the data relating to that state is retrieved from the ACPI storage area  210 ″. Once the power management states have been changed, the data contained within the ACPI storage areas  210 ′ and  210 ″ are updated and accordingly.  
         [0056]    If the embodiments are arranged to adopt a previous power management state, the data identifying that prescribed power management state is extracted from the wake-up network message and the OSPM software  214  is arranged to place the client machine in that prescribed power management state. Again, the data identifying the current and previous power management states are updated.  
         [0057]    Since the client machines are resumed, in preferred embodiments, to their former power management state, including restoration of their system context, the user is unaware that their machine bad entered a lower power management state. This has the significant advantage that the user is not inconvenienced by the power management policy of the organization.  
         [0058]    Referring to FIG. 5, there is shown a pair of flowcharts  500  for dealing with the situation where a user returns to their client machine having left it for a sufficient period of time to cause the client machine to enter the safe S3/quick S4 state and for the power management application  104  to cause that machine to enter an even lower power management state.  
         [0059]    The user, using the input device  224 , generates a wake-up event that is detected by the power management event detection logic  220 . The wake-up event is received at step  502 . At step  504 , the power management event logic  220  informs the wake-up and sleep logic  222  of the event which, in turn, causes the ACPI BIOS  210  to output a log-on screen that requests the user to input their user name and password. At step  506 , the user name and password are received. It is determined, at step  508 , whether a valid user name and password have been entered. If either of the user name or the password is invalid, an error message is output, at step  510 , containing an indication to that effect and control returns to step  504 .  
         [0060]    However, if a valid user name and password were entered at step  508 , it is determined, at step  512 , whether or not the client machine has previously been placed in a power management state by the power management application  104 . The data identifying whether or not the client machine has been placed in a power management state by the application  104  is stored in the BIOS storage areas  210 ′ and  210 ″ and is accessible via the ACPI BIOS  210 . If the determination is that the organisation&#39;s power management policy is in force, a message is output at step  514 , indicating that the client machine had entered a lower power state and that system restoration may take slightly longer than anticipated. Control then passes to step  516  where the system context is restored.  
         [0061]    However, if the organisation&#39;s power management policy is not in force, the system context of the client machine is retrieved from the HDD  226  and restored at step  516 . Since the wake-up event was user generated, preferably, the client machine is placed in the working state at step  518 .  
         [0062]    Having arisen from a sleep-state, that is, a power management state other than the working state, the client machine preferably transmits a network message to the power management application  104  at step  520 . The network message contains identification data for identifying the client machine to the server  102  and, preferably, an indication of the current working state of the client machine.  
         [0063]    The power management application  104  receives the transmitted network message at step  522 . In response to receiving the network message, the power management application  104 , at step  524 , extracts the client machine identification data and uses that extracted data to remove the client machine from the power state data  122 .  
         [0064]    It will be appreciated that the embodiments advantageously use the common interface for enabling robust operating system directed motherboard system configuration and power management (OSPM) of the client machines  106  to  110 . In particular, the Advanced Configuration and Power Interface (ACPI) specification assists in solving the above prior art problems. The current version of the ACPI is version 2, having a release date of Jul. 27, 2000 together with the ACPI Errata version 1.3, Nov. 27, 2000, both of which are incorporated herein by reference for all purposes.  
         [0065]    These standards define the following known power management states  600 , which are shown in and described with reference to FIG  6 .  
         [0066]    State S0: While a system or client machine is it state S0  602 , the system is said to be in a working state. The behaviour of that state is defined such that a processor  202 , or, in a multi-processor system, the processors are, in one of a number of so-called processor states, C 0    604 , C 1    606 , C 2    608 , . . . , C N    610 , which each represent varying degrees of processor operation and associated power consumption. The processor maintains the dynamic RAM context. Any devices  612 , such as first  614  and second  616  devices, connected to, or forming part of, the client machine are individually managed by the operating system software and can be in any one of four possible device states D0-D3, which, again, reflect varying degrees of power consumption. Any associated power resources arc arranged to be in a state that is compatible with the device states.  
         [0067]    State S1: The S1 state  618  is a low wake-up latency sleeping state. In this state, no system context is lost (CPU or chip set) and the system hardware maintains all system context.  
         [0068]    State S2: The S2 state  620  is also considered to be a low wake-up latency sleeping state. The S2 state  620  is substantially similar to the S1 state  618  but for the CPU and the system cache context being lost in the 52 state, since, typically, the operating system is responsible for maintaining cache and processor context.  
         [0069]    State S3: The S3 state  622  is a low wake-up latency sleeping state where all system context is lost except for system memory. The CPU, cache and chip set context are lost in thin state. However, the system hardware maintains memory context and restores some CPU and L2 configuration context.  
         [0070]    State S4: The S4 State  64  is the lowest power, longest wake-up latency, sleeping state supported by the ACPI. To reduce power consumption, preferably to a minimum, it is assumed test the hardware platform has powered-off all devices. Platform context is maintained.  
         [0071]    It will be appreciated that embodiments can be realised in which the power management states to the above described S0 to S4 states, providing the client machines, in those state, can still respond to a massage received from the power management application  104 .  
         [0072]    However, FIG. 7 shows a power management state and associated state transition diagram  700  for a preferred embodiment. The state transition diagram  700  comprises a working system state S0  702 . Preferably, convenional states S1  704  and S2  706  are also supported. The states S0-S2  702  to  706  are substantially identical in operation and realisation to the corresponding states described above in relation to FIG. 6.  
         [0073]    Additionally, the state diagram  700  illustrates a new state, that is, a Safe S3/Quick S4 state  708  (SS3/QS4). The behaviour of the client machine  106  in the SS3/QS4 state  708  can be characterized by the actions of saving substantially the same data as the conventional S3 state. Furthermore, in the SS3/QS4 state  708  only the RAM  206  remains in a powered state while all other aspects of the client machine  106  adopt substantially the same powered state of the conventional S3 state but for the network card  225  and the power management event detection logic  220  to allow a wake-up from the state.  
         [0074]    Therefore, if a power failure occurs while the system is in the SS3/QS4 state  708 , loading the data representing the system context is retrieved from the HDD  226  and the system context is established accordingly. In contrast, to the prior art power management state S3, if a power failure occurs, the system context is recoverable.  
         [0075]    In the absence of a power failure, the system context, when waking from the SS3/QS4 state  708 , can be restored within a relatively short period of time, such as, for example, 5 seconds, that is, within a time scale that is comparable to the wake-up time for a conventional S3 state but with the additional security of also being recoverable from a power failure, unlike the conventional S3 state.  
         [0076]    Preferably, once the context has been restored following a power failure, the system enters or resumes the SS3/QS4 state  708 . However, it will be appreciated that embodiments could be realised in which any one of the states are entered upon recovery, as can be seen from the optional presence of the conventional S3  710  and S4  712  states.  
         [0077]    Furthermore, even though the above embodiments have been described in terms of having a number of system states, the present invention is not limited to such system states. Embodiments can be realized in which other states such as, for example, Legacy states, mechanical-off states G3 and soft-off S5 states are also supported.  
         [0078]    It will be appreciated that the power management application  104  can instruct the client machines to assume any one of the power management states illustrated in FIGS. 6 and 7.  
         [0079]    Although the above embodiments use an HDD  226  as the non-volatile storage medium, it will be appreciated that other forms of non-volatile storage media may be used. For example, a locally or remotely accessible flash-memory may be used to store the data to allow recovery from a power failure or to allow wake-up from a sleep state Alternatively, a remotely, or network accessible, HDD can be used to store the system context.  
         [0080]    Furthermore, although the above embodiments have been described with reference to client machines reporting to the power management application that a reduced power consumption state has been entered, the present invention is not limited to such arrangements. Embodiments can be realised that report entry into the working state, preferably, in addition to reporting entry into a reduced power consumption state of the power management states. Therefore, the data  122  stored on the HDD  120  of the power management server  102  will store data identifying the client machines with which it can communicate and their corresponding power management states.  
         [0081]    Although the above embodiments have been described with reference to client machines being placed in a power saving mode using a LAN and a server of the organisation, the present invention is not limited to such arrangements. Embodiments can be realised in which a communication device, provided by the energy supplier, is interfaced with a client machine. The communication device is arranged to supply the commands to the OSPM to enter or to recover from a reduced power consumption power management state. The communication device may operate according to a predetermined schedule. Alternatively, or additionally, the communication device may receive wireless commands from a transmitter and control centre of the energy supplier. These wireless commands may be used to control the power management states of the client machine to which the communication device is attached.  
         [0082]    It will be appreciated that the client machines can be addressed by the power management application  104  either globally, using some form of broadcast message, or individually using corresponding addresses. Furthermore, the globally addressed or individually addressed client machines may be placed in the same power management state or in respective power management states.  
         [0083]    Although the power management application  104  retrieves the power state data  122  from the HDD  120  and uses that data to instruct various client machines to enter a power saving mode of operation, the present invention is not limited to such embodiments. Embodiments can be realised in which the power management application  104  transmits a broadcast message to all machines connected to the intranet or PC park. In such embodiments, the client machines will respond accordingly. If the client machine is in a working state, the client machine may be configured to ignore the request. Alternatively, the client machine may simply output an indication of the receipt of the request to the user, who may then decide whether or not to enter a power saving mode of operation. If the client machine is already in a power saving mode of operation, such as the safe S3/quick S4 state, or is in a stand-by state, the client machine, in response to receiving the broadcast message, will enter the lowest power saving state of operation. If the broadcast message contains an indication of the preferred power state to be adopted, the client machine, when appropriate, will assume that prescribed state of operation.  
         [0084]    The above embodiments have been described with reference to placing a client machine in a power saving state. However, the present invention is not limited to such an arrangement. Embodiments can equally well be realised in which other devices or apparatus are placed in a power saving state. For example, the printers, fax machines, digital senders, scanners, photocopiers and other electronic devices that are connected to the organisations intranet, or that are used by the organisation, may be arranged to enter an appropriate power saving mode of operation during a period for which the organisation&#39;s power management policy is in force. It will be appreciated that any such devices or apparatus would preferably need access to non-volatile storage to preserve their system context, if needed. In effect, embodiments may be realised using any ACPI compliant devices.  
         [0085]    It will be appreciated that the data collected by the server on when power saving measures were in force may be used to provide evidence to the energy supplier that the organisation has complied with its agreement with the energy supplier.  
         [0086]    It will be appreciated that in a stand-by state of the power management states, that is, in the safe S3/quick S4 state, a client machine may consume about 5 Watts per hour whereas in a hibernate state the client machine consumes about 2 or 3 Wkatts per hour. In both instances, the power consumed is less than that of the working state S0.  
         [0087]    The reader&#39;s attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.  
         [0088]    All of the features disclosed in this specification (including any accompanying claims, abstract and drawings, and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.  
         [0089]    Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar propose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.  
         [0090]    The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.