referring now to the drawings , one embodiment as shown in fig1 includes a microprocessor ( 10 ), such as an intel 80386 , which is conventionally connected to the memory and other circuitry of a microprocessor - based device through data ports coupled to the data bus of the device at 11 . the multiple - input and gates ( 12 ) and ( 14 ) are connected to the address lines of the microprocessor at 13 . each gate monitors separate addresses generated by the microprocessor which represent a request for high speed operation or low speed operation . these gates drive a set / reset latch ( 16 ) so that a logical high from gate ( 12 ) latches a high output from the latch ( 16 ) and a logical high from gate ( 14 ) resets the output of latch ( 16 ) low . through addressing constraints , both gates ( 12 ) and ( 14 ) are prevented from being high simultaneously , avoiding error conditions . the output of latch ( 16 ) supplies the + hi /− lo signal for driving the speed latch to be subsequently described . it is understood that other circuit configurations could be utilized to monitor designated address locations of the microprocessor to determine whether all of the data processing ability of the microprocessor is demanded based upon the determination of a critical instruction or the reoccurrence of non - critical instructions as previously described . the circuit utilized to monitor the operation of the microprocessor 10 can utilize commonly available circuitry provided on the microprocessor itself or alternately can have an external circuit placed in the substrate of the microprocessor chip itself or as a separate structure coupled to a microprocessor . as shown in fig1 the circuit utilized for monitoring the operation of the microprocessor 10 is coupled to the address bus of the system wherein instruction information can be placed in designated addresses to indicate the operation of the microprocessor . alternatively , critical operation of the microprocessor may be determined by direct coupling of a monitoring circuit to the data bus of the system or directly to the data stream input or output from the microprocessor itself . as will be subsequently described , a list of predetermined critical instructions or non - critical instructions may be compiled and placed in memory within the system to which to compare for a determination of the microprocessor operation and subsequently the speed at which operation is required . the monitoring module may thus be coupled to memory of the system for access to such a list or include the list within memory provided therewith . in any case , the operation of the microprocessor 10 is monitored and the monitoring module will enable a request for high or low speed operation accordingly . oscillator ( 18 ) is a commercial integrated circuit , such as type 82384 , that simultaneously develops two output frequencies clk 1 and clk 2 at 24 and 26 respectively from a single crystal ( 20 ), in this case clk 2 being twice the frequency of clk 1 , but in any case clk 2 is greater and most conveniently a multiple of clk 1 . the oscillator 18 and crystal 20 are coupled to a source of power through transformer 22 to generate the desired frequencies . each of these outputs 24 and 26 are separately connected to a control or oscillator latch 28 comprising , in a simple form , a pair of and gates 30 and 32 and an or gate 34 . the outputs 24 and 26 of the oscillator 18 are input into the an gates 30 and 32 respectively in the frequency control latch 28 . the other input of high frequency select gate ( 30 ) is directly connected to the = hi /− lo signal generated by latch ( 16 ). the other input of low frequency select gate ( 32 ) is connected to the = hi /− lo signal through an invertor ( 36 ). the outputs of gates ( 30 ) and ( 32 ) are added together in or gate ( 34 ), the output of which corresponds to the pulse train developed as clk 1 or clk 2 at 24 and 26 from the oscillator 18 , depending on the state of the + hi /− lo signal . this output is connected to the clock input of the controlled microprocessor 10 at 38 . the circuitry as shown in fig1 is very much simplified but will function to provide distinct frequencies for operation of the microprocessor as desired . other circuitry to accomplish this result is contemplated by the present invention and could include a combination of and gates and invertors which may function more efficiently and be an easier configuration to utilize . turning now to fig2 a flow chart of a monitor process which may be performed by the microprocessor in fig1 is shown . this process is performed periodically as determined by an independent system timer that generates an interrupt , initiating the process . as an example , the monitoring function may be keyed to a time interrupt which in an ibm personal computer happens 18 . 2 times per second such that the monitoring function will occur continuously during operation of the device and will act to automatically reduce the speed of operation if the microprocessor is being utilized in a non - critical matter . the independent timer and interrupt are part of the standard design of portable microprocessor - based devices . upon the occurrence of the timer interrupt , the process will start at a predetermined address in the instruction stream of the microprocessor at 50 . the process will then search backward in the instruction stream , instruction by instruction , at 52 wherein each address searched will be checked to see if an interrupt or critical instruction occurred at 54 and 56 respectively . the process will thus verify whether the checked instruction is an interrupt other than the input or keyboard interrupt at 54 . if so , it has found a critical instruction and immediately exits the timer interrupt service routine and performs the high speed exit routine at 60 to be subsequently described . if the instruction is not an interrupt , the process will verify whether the instruction is one of the critical instructions at 56 , that is , one that might be used in an operation for which - performance is critical . if the instruction is critical , the process immediately exits the timer interrupt routine and runs the high - speed exit routine 60 . if neither critical condition is present , the process loops back to step 52 to continue stepping back one instruction at time . after is has stepped back a predetermined number of instructions as compared at 58 , it steps forward a similar number of instructions at steps 62 , checking for interrupts at step 64 , critical instructions at step 66 , and looping as in the step - back procedure . if after evaluating all of these instructions the process locates no interrupts or critical instructions , it increments the inactivity counter at 70 , and checks the counter for its predetermined critical value at 72 . if the critical value has not been achieved , the program ends the interrupt service routine at 74 . if the critical value has been reached , the program issues an instruction to trigger the low - speed latch at 76 , then exits the interrupt service routine at 74 . if the critical value has been exceeded , the program decrements the inactivity counter at 78 in effect keeping its value constant , then the process ends the interrupt service routine at 74 . the high - speed exit routine 60 verifies whether the operating speed of the system is high at 80 . if it is high , the routine resets the inactivity counter at 82 . if the speed is low , it sets the speed latch high at 84 , then resets the inactivity counter at 82 , after which the program exits the interrupt service routine at 74 . it should thus be seen that when the monitoring routine searches a predetermined number of instructions in the instruction stream of the microprocessor , a determination can be made whether operation of the microprocessor is critical necessitating high speed operation . as the interrupt service routine is conducted many times per second , the operation of the microprocessor will automatically be conducted at the proper operating speed in order to conserve battery power to its fullest extent . it should be evident that the system may also be manually operated by having the interrupt service routine placed in a predetermined address which can be selected to invoke a desired operating speed by the user . it is not thought that manual operation would necessarily be useful as under most circumstances , the user will not necessarily know when performance of the microprocessor is critical and this function can be accomplished automatically using the techniques of the present invention . in the interrupt service routine as shown in fig2 the microprocessor itself analyzes the instruction stream searching for an interrupt or critical instruction as described . the particular number of steps used in the searching routine is not critical and may be selected to provide optimum efficiency . a list of critical instructions for each family of microprocessors can be provided in a look up table which can be stored in memory such as a random access memory ( ram ) or a read only memory ( ram ) or anywhere that the microprocessor has access to such as list . alternatively , an external processor may be provided having its own eprom memory containing such a list or the list can be hard wired into the microprocessor chip itself . it should also be recognized that although the invention has been described with reference to a determination of an interrupt or critical instruction , the interrupt service routine can also operate to determine the occurrence or reoccurrence of a series of non - critical instructions which may indicate house keeping or other routine functions such as polling of the keyboard , parity checking or other similar functions . the present invention thus provides a simple and yet effective way in which to reduce power consumption by a microprocessor and therefore of a microprocessor - based system which is operated from a stored energy source . as an example , a first oscillator frequency of 16 mhz . may be provided for high speed operation which may provide less than one hour of computing time due to depletion of a battery source utilized therewith . utilizing this invention , a second oscillator frequency of 4 mhz . may be provided for low speed operation of the system during non - critical performance needs which will have the effect of extending the useful life of the system to over two hours under most circumstances . it is recognized that any operating frequencies may be provided for the particular tasks to be accomplished by the microprocessor - based system , such as for example a high speed operating frequency of 33 mhz . being the state of the art at the present time to a low speed operating frequency of 4 mhz . which is adequate for processing key strokes and the like . it can thus be seen that use of the present invention will extend the useful life of the microprocessor - based system easily by a factor of two or more from which the benefits should be apparent . although the present invention has been described with reference to a particular embodiment thereof , this is meant to be illustrative only and is not to be construed as limiting the scope of the invention . various modifications and changes will occur to those skilled in the art without departing from the spirit and scope of the present invention as defined in the appended claims .