the power management system of the present invention can be implemented in hardware , software , firmware , or a combination thereof . in the preferred embodiment ( s ), the system is implemented in software or firmware that is stored in a memory and that is executed by a suitable instruction execution system . if implemented in hardware , as in an alternative embodiment , the system can implemented with any or a combination of the following technologies , which are all well known in the art : a discrete logic circuit ( s ) having logic gates for implementing logic functions upon data signals , an application specific integrated circuit having appropriate logic gates , a programmable gate array ( s ) ( pga ), a fully programmable gate array ( fpga ), etc . referring now to the drawings , wherein like reference numerals designate corresponding parts throughout the drawings , fig1 illustrates a power management system 100 that includes a computer or processor based system 2 having a peripheral component interconnect ( pci ) bus 4 , and therefore a pci chip set 6 . the computer system 2 generally comprises a computer processor 8 , a local bus 10 , a storage device 12 , and a computer memory 14 with an operating system 16 . the computer processor 8 accepts data from computer memory 14 over the local bus 10 . it should be noted that while the computer system 2 is described as having a local bus 10 , an alternative dedicated path may be used . the computer system 2 also includes an input device ( s ) 18 and output device ( s ) 20 . generally , this system 2 may run any of the number of different platforms and operating systems 16 , including , but not limited to , the unix ®, windowsnt ®, or sunsolaris ® operating systems . a pci slot 22 is attached to the pci bus 4 and provides a means for a peripheral device 17 , having a memory 21 , such as a network interface card ( nic ), to attach to the computer system 2 . the peripheral device 17 attached to the computer 2 may be any of a number of devices , such as , for example , a fax modem card , video accelerator card , or a sound card . in accordance with the preferred embodiment of the invention , the peripheral device 17 and the operating system 16 of the computer 2 logically interact , as described with reference to fig2 thereby providing the present power management system 100 . it should be noted that more than one peripheral device may be provided by the present power management system 100 . fig2 is a flow chart illustrating the functionality of the power management system 100 for providing pci power management support without requiring a clock , in accordance with the preferred embodiment of the invention . generally , the flow chart of fig2 shows the architecture , functionality , and operation of a possible implementation of the power management system . in this regard , each block represents a module , segment , or portion of code , which comprises one or more executable instructions for implementing the specified logical function ( s ). it should also be noted that in some alternative implementations , the functions noted in the blocks may occur out of the order noted in fig2 . for example , two blocks shown in succession in fig2 may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order , depending upon the functionality involved , as will be further clarified hereinbelow . as shown by block 102 , at the power - up stage of the computer 2 , device drivers , which have been previously stored in the storage device 12 of the computer 2 , are loaded into the memory 14 and executed by the processor 8 . as is well known to one of reasonable skill in the art , device drivers are controlled and supervised by the computer &# 39 ; s operating system 16 , which as previously mentioned , is located in the computer memory 14 and executed by the processor 8 . the device drivers contain functionality pertaining to the peripheral devices 17 that are attached to the computer 2 via the pci slot 22 . generally , the device drivers enable the computer system 2 to interface with the peripheral device . as such , the device drivers provide for such features as the data sampling speed of peripheral devices 17 , flow control , data control , or peripheral device 17 status . further , the device drivers specify functions to be performed when a source , external to the computer 2 , such as a fax modem card having a pci interface , request a responding action to be performed by the computer 2 , as defined by a device driver . as an example , a responding action may include , but is not limited to , a request for the computer &# 39 ; s operating system 16 to provide the fax modem card with appropriate power and clock , for purposes of receiving an incoming fax . alternatively , the external request may be derived from a device external to a peripheral device 17 , which is attached to the computer 2 . as such , the external request would be received by the peripheral device 17 , which would , in turn , require a responding action to be performed by the computer 2 , as defined by a device driver . during execution of the device drivers , each peripheral device 17 is individually identified by a pme_status bit , which is stored in a configuration register space , located in the peripheral device memory 21 . the pme_status bit is a read bit that is continuously polled by the device driver software . in accordance with the preferred embodiment of the invention , as shown by block 104 , the computer 2 enters a sleep state after a period of peripheral device 17 inactivity . sleep states may differ from one computer to another in accordance with specific requirements of the computer user , as specified by the power management software . in accordance with the preferred embodiment of the invention , the sleep state provides a reduction in the clock speed of the computer 2 such that the computer processor 8 is allowed to continue performing background tasks , such as monitoring mouse movement , or running screen saver , that use a small fraction of the computer system &# 39 ; s processor capacity . it should be noted that the computer 2 may employ numerous internal clocks , as opposed to a single clock . in such a case , the power management software may include logic to reduce the clock speed of each individual internal clock accordingly . during the sleep state , the clock signal is not transmitted to peripheral devices 17 connected to the computer 2 . this further reduces power consumption by the computer 2 . alternatively , the clock may be completely turned off . to trigger the sleep state , power management software is loaded into the computer memory 14 , wherein the power management software is capable of detecting inactivity of peripheral devices 17 connected to the computer 2 . the period of peripheral device 17 inactivity is predefined and user specified via the power management software . as shown by block 106 , while the computer is in a sleep state , an external event may occur that is perceived by a peripheral device attached to the computer 2 . as an example , an external event may be a phone ring , received from a phone jack located separately from the computer 2 , and perceived by a fax modem card that is connected to the computer 2 via the pci slot 22 . thereafter , as depicted in block 108 , in response to the external event , the peripheral device 17 receives an external action request from the source of the external event . the external action request specifies to a peripheral device 17 , such as the fax modem of the present example , that a response is needed by the peripheral device 17 . in response to the external action request , the pme_status bit is set , thereby signifying that there has been a peripheral device 17 request ( block 110 ). as shown by block 112 , after the peripheral device 17 has received the external action request , the peripheral device 17 notifies the computer &# 39 ; s operating system 12 that an external event involving power management has occurred . in accordance with the preferred embodiment of the invention , notification is performed by a power management event ( pme ) signal . the pme signal notifies the computer &# 39 ; s operating system 16 of the external event by transmitting from the peripheral device 17 , via the pci bus 4 , to the pci chip set 5 , which notifies the pci chip set 5 that a power management event has occurred . the pci chip set 6 , in turn , notifies the operating system 16 of the external event . as depicted by block 114 , in response to receiving the pme signal , the computer system 2 wakes up from its sleep state , such that the computer system 2 functions as it did before the sleep state . as shown in block 116 , the operating system 16 then attempts to determine the source of the pme signal . in determining the source of the pme signal the operating system 16 requests each device driver , associated with a peripheral device 17 attached to the computer 2 via pci slots 22 , to poll its correlating peripheral device 17 . during polling , each device driver searches the associated peripheral device 17 for a set pme_status bit . the device driver polls these bits in each peripheral device &# 39 ; s 17 predefined location within the configuration space . if the pme_status bit is set , this signifies that the associated peripheral device 17 is signaling a power management event . as noted by block 118 , when the operating system 16 identifies which peripheral device 17 transmitted the pme signal , the operating system 16 initiates the device driver associated with the peripheral device 17 to perform associated predefined functions as specified by the device driver . as previously mentioned , the functions to be performed by and for the peripheral device 17 are previously loaded by the device drivers in the computer processor 8 , which is managed by the operating system 16 . among the many functions defined by the device drivers , the device drivers also define clock requirements , which are to be performed by the pci chip set 6 . as such , in accordance with the device driver loaded by the operating system 16 , the pci chip set 6 initiates the internal clock , such that the peripheral device 17 is capable of performing the predefined functions according to the associated device driver . fig3 is a flow chart illustrating logic performed by the operating system 16 of fig1 . as shown by block 202 , in accordance with the preferred embodiment of the invention , the computer is first initialized . during initialization of the computer 2 , the operating system 16 loads device drivers , previously stored in the storage device 12 , into the memory 14 for execution by the processor 8 . during execution of the device drivers , the operating system 16 assigns a pme_status bit , stored in a configuration register space , located in the peripheral device memory 21 , to peripheral devices 17 that have been removably attached to the computer 2 . as shown by block 204 , the operating system 16 then determines whether the computer 2 should enter a sleep state based on a predefined period of peripheral device 17 inactivity . assuming that the computer 2 enters a sleep state , the operating system 16 moves to block 206 to wait for a pme signal . as shown by block 208 , if the pme signal is not received by the operating system 16 in block 206 , the computer 2 remains in a sleep state . upon receiving a pme signal in block 206 , the operating system 16 proceeds to block 208 and wakes the computer 2 . as shown by block 210 , the operating system 16 then attempts to determine the source of the pme signal by polling , via use of device drivers , peripheral devices 17 that are removably connected to the computer 2 for a set pme_status bit . when the source of the pme signal has been found , the operating system 16 initiates the device driver associated with the peripheral device that transmitted the pme signal . ( block 212 ). fig4 is a flow chart illustrating logic implemented in the peripheral device 17 . the logic is implemented by the peripheral device 17 of fig1 after the computer 2 enters a sleep mode . in accordance with the preferred embodiment of the invention , when the computer 2 enters a sleep mode , it turns off power to the peripheral device 17 that is removably attached to the computer 2 , thereby also placing the peripheral device 17 into a sleep state ( block 222 ). in block 224 the peripheral device 17 remains in a sleep state until it receives an external action request . in response to receiving the external action request , in block 226 the peripheral device 17 transmits the pme signal to the operating system 16 of the computer 2 . then , in block 228 , the peripheral device 17 is turned on by the computer 2 . as shown by block 230 , once the peripheral device 17 is turned on , it performs functions predefined by device drivers executed by the computer processor 8 and initiated by the operating system 16 as previously described with reference to fig2 ( block 230 ). in accordance with a first alternative embodiment of the invention , a separate clock source may be located on a peripheral device 17 that supplies the computer system 2 with an external clock , even if the computer &# 39 ; s internal clock is off ( i . e ., d 3 cold state ). based upon this external clock , the computer 2 is capable of sampling external events and detecting a pme . in a second alternative embodiment of the invention , the computer 2 includes functionality to enable or disable the power management features when required by a particular peripheral device 17 . this is accomplished by including a pme_enable bit that is stored in the configuration register space , located in the peripheral device memory 21 . similar to the pme_status bit , during execution of the device drivers , each peripheral device 17 is associated with a particular pme_enable bit . in accordance with the second alternative embodiment , prior to a pme occurring , the device driver associated with a peripheral device 17 sets the pme_enable bit . if the pme_enable bit is set prior to a pme occurring , the computer 2 recovers from sleep state as described with reference to the preferred embodiment of the invention . if however , the pme_enable bit is not set by the device driver prior to a pme occurring , the associated peripheral device 17 will not transmit a pme signal to the computer , and therefore will not be part of the power management scheme . as such , the computer will not recover from the sleep state if the pme_enable bit associated with the peripheral device 17 is not set . it should be emphasized that the above - described embodiment of the present invention , particularly any “ preferred ” embodiments , are merely possible examples of implementations , merely set forth for a clear understanding of the principles of the invention . many variations and modifications may be made to the above - described embodiment ( s ) of the invention without departing substantially from the spirit and principles of the invention . all such modifications and variations are intended to be included herein within the scope of the present invention and protected by the following claims .