a mode of implementation of the present invention will be described in detail below with reference to the drawings . referring to fig1 a mode of implementation of the invention is configured of a computer 100 operating under programmed control ; input / output units 1 , connected to the computer 100 , into which users enter input / output requests or confirmations of input / output completion ; and auxiliary memory units 3 . in a variation of this mode of implementation , the computer 100 and a recording medium 101 such as a magnetic disk unit or a semiconductor memory may be connected to each other via a signal line , so that the computer 100 executes the following processing under a program loaded from the recording medium 101 via the signal line . the computer 100 comprises input / output means 2 for receiving input / output requests or confirmations of input / output completion entered by users ; io queues 4 for holding input / output requests , each corresponding to one or another of the auxiliary memory units 3 ; io queue incorporating means 5 for incorporating into one or another of the io queues 4 an io command 10 holding the reserve position of a user &# 39 ; s input / output request and the user &# 39 ; s local chain ; local chain manipulating means 6 for manipulating reserve positions in io commands 10 and local chains ; and actual io issuing means 7 for taking out io commands 10 from io queues 4 and processing physical input / output ( physical io ) upon auxiliary memory units 3 . fig2 is a flow chart which illustrates processing by the input / output means 2 ; fig3 is a flow chart which illustrates processing by the local chain manipulating means 6 ; fig4 is a flow chart which illustrates processing by the io queue incorporating means 5 ; and fig5 is a flow chart which illustrates processing by the actual io issuing means 7 . next , the overall operation of this mode of implementation will be described in detail below with reference to fig1 to 5 . first will be described a case in which a user makes an input / output request by entering an io command 10 at an input / output unit 1 . referring to fig1 the input / output means 2 determines whether the user &# 39 ; s request entered into the input / output unit 1 is an input / output request or a confirmation of input / output completion ( step 201 ) and , if it is determined to be an input / output request , incorporates with the local chain manipulating means 6 the io command 10 into the user &# 39 ; s local chain ( step 202 ). the input / output means 2 , with the io queue incorporating means 5 , further incorporates the io command 10 into the io queue 4 corresponding to a designated auxiliary memory unit 3 ( step 203 ), and completes the processing . if the user &# 39 ; s request is determined to be a confirmation of input / output completion at step 201 , the input / output means 2 waits until physical io on the io command 10 , whose input / output completion is to be confirmed , is completed ( step 204 ) and , upon completion of the input / output processing , separates with the local chain manipulating means 6 the io command 10 from the user &# 39 ; s local chain ( step 205 ), thereby completing the processing . referring to fig3 the local chain manipulating means 6 , as instructed by the input / output means 2 , picks out the local chain of the user having requested input / output ( step 301 ), determines whether the instruction by the input / output means 2 requires incorporation of the io command 10 into the local chain or its separation from the local chain ( step 302 ) and , if it is determined to be a request for separation , separates the io command 10 from the local chain ( step 303 ) or , if it is determined to be a request for incorporation , adds the io command 10 at the end of the local chain ( step 304 ). the local chain manipulating means 6 further alters the reserve position of the io command 10 in the local chain according to the sequence of the chain ( step 305 ), and completes the processing . referring to fig4 the io queue incorporating means 5 , as instructed by the input / output means 2 , incorporates the io command 10 into the io queue 4 corresponding to the auxiliary memory unit 3 designated by the input / output request ( step 401 ), and completes the processing . referring to fig5 the actual io issuing means 7 temporarily holds the leading one of the io commands 10 stored in the io queue 4 corresponding to an auxiliary memory unit 3 ( step 501 ), compares the reserve position of the temporarily held io command with that of the following io command 10 , temporarily holds whichever of the io commands 10 is earlier in the reserve position , and repeats this procedure on every io command 10 stored in the io queue 4 ( steps 502 to 505 ). the actual io issuing means 7 , after the completion of step 505 , separates the temporarily held io command from the io queue 4 ( step 506 ), and performs physical 10 corresponding to the temporarily held io command on the auxiliary memory unit 3 ( step 507 ). the actual io issuing means 7 repeats physical io on the auxiliary memory unit 3 as long as any io command 10 is stored in the io queue 4 ( step 508 ). the actual io issuing means 7 performs the above - described processings of steps 501 to 508 for io queues 4 corresponding to all the auxiliary memory units 3 . next will be described in detail a preferred embodiment of the invention with reference to fig6 to 13 . fig6 is a block diagram of the preferred embodiment of the invention , consisting of a user process 610 ; input / output means 620 for receiving input / output requests and confirmations of input / output completion entered by users ; a plurality of magnetic disk units 680 and 690 for storing data ; an io queue 650 for holding an io command 612 correspondingly to the magnetic disk unit 680 ; an io queue 660 for holding the address of an io command 613 correspondingly to the magnetic disk unit 690 ; io queue incorporating means 640 for incorporating the io commands 612 and 613 into the io queues 650 and 660 , respectively ; local chain manipulating means 630 for manipulating the reserve positions of the io commands 612 and 613 and a local chain ; and actual io issuing means 670 for taking out the io commands 612 and 613 from the io queues 650 and 660 , respectively , and performing physical inputting / outputting . each individual user process 610 comprises the io commands 612 and 613 for holding the reserve positions of input / output requests and the local chain , and a local chain start 611 for storing the address of the leading io command of the local chain . the io command 612 comprises the disk number of the magnetic disk unit 680 for performing physical inputting / outputting ; an io address , which is the address of the object of inputting / outputting in the magnetic disk unit 680 ; the local chain for chaining the io command 612 in the user process ; and a reserve position indicating the position of the input / output request in the reserve sequence . similarly , the io command 613 comprises the disk number of the magnetic disk unit 690 ; an io address , which is the address of the object of inputting / outputting in the magnetic disk unit 690 ; the local chain for chaining the io command 613 ; and a reserve position . the io queue 650 is provided with the disk number of the magnetic disk 680 ; the number of held items , which is the number of input / output requests in the io queue ; the io command address of the io command 612 requested for inputting / outputting ; and a position in sequence . similarly , the io queue 660 is provided with the disk number of the magnetic disk 690 ; the number of held items ; the io command address of the io command 613 requested for inputting / outputting ; and a position in sequence . fig7 is a diagram illustrating the state before user a and user b request input / output processing ; fig8 a diagram illustrating the state after user a and user b have requested input / output processing ; fig9 a diagram illustrating the state after the completion of physical io ; fig1 , a diagram illustrating the state after user a has confirmed the completion of input / output ; fig1 , a diagram illustrating the state after user b has confirmed the completion of input / output ; fig1 , a diagram illustrating the state after physical io has been performed in the state of fig1 ; fig1 , a diagram illustrating the state after physical io has been performed in the state of fig1 . next will be described the operation of the preferred embodiment of the invention with reference to fig7 to 13 . the following description refers to a case of processing in which users a and b are supposed to issue three and two input / output requests , respectively , to two magnetic disk units . referring to fig7 user a &# 39 ; s process 710 comprises three io commands 712 to 714 and a local chain start 711 indicating a value of “− 1 ” meaning the presence of no input / output request . user b &# 39 ; s process 720 comprises two io commands 722 and 723 and a local chain start 721 indicating a value of “− 1 ” meaning the presence of no input / output request . in io queues 730 and 740 respectively corresponding to the magnetic disk units 750 and 760 , the number of held items in every io queue is “ 0 ” indicating the absence of any address of an io command to perform physical io . fig8 illustrates the state following the state of fig7 in which user a and user b have requested input / output processing . the input / output means , having received input / output requests by the io commands 712 to 714 , calls the local chain manipulating means and the io queue incorporating means successively , and then the input / output means , having received input / output requests by the io commands 722 and 723 , calls the local chain manipulating means and the io queue incorporating means successively . the input / output means , having successively received the io commands 712 to 714 , incorporates with the local chain manipulating means the io commands 712 to 714 into user a &# 39 ; s local chain . the local chain manipulating means , accepting the io command 712 , recognizes that user a &# 39 ; s local start 711 is “− 1 ” and that the chain is vacant , stores the address al of the io command 712 at the local chain start 711 in order to position the io command 712 in the leading position of the chain , and stores “ 1 ” in the reserve position of the io command 712 . then the local chain manipulating means , accepting the io command 713 , recognizes user a &# 39 ; s last io command 712 from the fact that the local chain - is “− 1 ”, stores the address a 2 of the io command 713 into the local chain of the io command 712 in order to position the io command 713 next to the io command 712 , and stores “ 2 ” in the reserve position of the io command 713 . further the local chain manipulating means , accepting the io command 714 , recognizes user a &# 39 ; s last io command 713 from the fact that the local chain is “− 1 ”, stores the address a 3 of the io command 714 into the local chain of the io command 713 in order to position the io command 714 next to the io command 713 , and stores “ 3 ” in the reserve position of the io command 714 . next the io queue incorporating means , referring to the disk number of the io command 712 , stores the address a 1 of the io command 712 into the io queue 730 corresponding to the magnetic disk 750 indicated by the disk number d 1 in a position whose sequential position is the number of items held in the io queue 730 plus 1 to make the number of items held in the io queue 730 “ 1 ”. the io queue incorporating means , referring to the disk number of the io command 713 , stores the address a 2 of the io command 713 into the io queue 740 corresponding to the magnetic disk 760 indicated by the disk number d 2 in a position whose sequential position is the number of items held in the io queue 740 plus 1 to make the number of items held in the io queue 740 “ 1 ”. further the io queue incorporating means , referring to the disk number of the io command 714 , stores the address a 3 of the io command 714 into the io queue 730 corresponding to the magnetic disk 750 indicated by the disk number d 1 in a position whose sequential position is the number of items held in the io queue 750 plus 1 to make the number of items held in the io queue 750 “ 2 ”. the io queue incorporating means , having similarly accepted the io commands 722 and 723 , incorporates with the local chain manipulating means the io commands 722 and 723 into user b &# 39 ; s local chain . the local chain manipulating means accepts the io command 722 , recognizes that user b &# 39 ; s local start 721 is “− 1 ” and that the chain is vacant , stores the address b 1 of the io command 722 at the local chain start 721 in order to position the io command 722 in the leading position of the chain , and stores “ 1 ” in the reserve position of the io command 722 . then the local chain manipulating means , accepting the io command 723 , recognizes user b &# 39 ; s last io command 722 from the fact that the local chain is “− 1 ”, stores the address b 2 of the io command 723 into the local chain of the io command 722 in order to position the io command 723 next to the io command 722 , and stores “ 2 ” in the reserve position of the io command 723 . next the io queue incorporating means , referring to the disk number of the io command 722 , stores the address b 1 of the io command 722 into the io queue 740 corresponding to the magnetic disk 760 indicated by the disk number d 2 in a position whose sequential position is the number of items held in the io queue 740 plus 1 to make the number of items held in the io queue 740 “ 2 ”. further the io queue incorporating means , referring to the disk number of the io command 723 , stores the address b 2 of the io command 723 into the io queue 730 corresponding to the magnetic disk 750 indicated by the disk number d 1 in a position whose sequential position is the number of items held in the io queue 730 plus 1 to make the number of items held in the io queue 730 “ 3 ”. fig9 is a diagram illustrating the state following the state of fig8 in which the actual io issuing means has taken out one io command address each from the io queues 730 and 740 and performed physical io upon the respectively corresponding magnetic disks 750 and 760 . the state of neither the local chain start nor the io commands is changed . the actual io issuing means successively refers to the io commands 712 , 714 and 723 in the io queue 730 , respectively indicated by the io command addresses of sequential positions 1 to 3 in fig8 ; takes out of the io queue 730 the io command 712 , first found from the io commands having the earliest reserve positions ; successively advances the io command addresses whose sequential positions follow those taken out ; and reduces the number of items held in the io queue 730 by 1 to “ 2 ”. then it performs physical io upon the magnetic disk 750 indicated by the disk number of the taken - out io command 712 . similarly , the actual io issuing means successively refers to the io commands 713 and 722 in the io queue 740 , respectively indicated by the io command addresses of sequential positions 1 to 2 ; takes out of the io queue 740 the io command 722 , first found from the io commands having the earliest reserve positions ; successively advances the io command addresses whose sequential positions follow those taken out ; and reduces the number of items held in the io queue 740 by 1 to “ 1 ”. then it performs physical io upon the magnetic disk 760 indicated by the disk number of the takenout io command 722 . fig1 illustrates the state following the state of fig9 in which user a has entered a confirmation of the completion of inputting / outputting of the io command 712 . the states of user b &# 39 ; s local chain start 721 , the io commands 722 and 723 , the io queues 730 and 740 , and the magnetic disks 750 and 760 are not changed . the input / output means , having received a confirmation of input / output completion on the io command 712 from user a , calls the local chain manipulating - means after the completion of physical io on the io command 712 . the local chain manipulating means , in order to separate the io command 712 from user a &# 39 ; s local chain , stores the value “ a 2 ” of the local chain of the io command 712 into the local chain start 711 and “− 1 ” into the local chain of the io command 712 . then , while successively referring to io commands , using the local chain , from the io command 713 indicated by the value “ a 2 ” of the local chain start 711 until the value of the local chain becomes “− 1 ”, it stores the sequential positions referred to as reserve positions in io commands , and the io commands 713 and 714 take on reserve positions “ 1 ” and “ 2 ”, respectively . fig1 illustrates the state following the state of fig1 in which user b has entered a confirmation of the completion of inputting / outputting of the io command 722 . the states of user a &# 39 ; s local chain start 711 , the io commands 712 to 714 , the io queues 730 and 740 , and the magnetic disks 750 and 760 are not changed . the input / output means , having received a confirmation of input / output completion on the io command 722 from user b , calls the local chain manipulating means after the completion of physical io on the io command 722 . the local chain manipulating means , in order to separate the io command 722 from user b &# 39 ; s local chain , stores the value “ b2 ” of the local chain of the io command 722 into the local chain start 721 and “− 1 ” into the local chain of the io command 722 . then , while successively referring to io commands , using the local chain , from the io command 723 indicated by the value “ b2 ” of the local chain start 721 until the value of the local chain becomes “− 1 ”, it stores the sequential positions referred to as reserve positions in io commands , and the io command 723 takes on a reserve position “ 1 ”. fig1 is a diagram illustrating the state following the state of fig1 in which the actual io issuing means has taken out one io command address each from the io queues 730 and 740 and performed physical io upon the respectively corresponding magnetic disks 750 and 760 . the state of neither the local chain start nor the io commands is changed . the actual io issuing means successively refers to the io commands 714 and 723 in the io queue 730 , respectively indicated by the io command addresses of sequential positions 1 to 2 ; takes out of the io queue 730 the io command 714 , first found from the io commands having the earliest reserve positions ; successively advances the io command addresses whose sequential positions follow those taken out ; and reduces the number of items held in the io queue 730 by 1 to “ 1 ”. then it performs physical io upon the magnetic disk 750 indicated by the disk number of the taken - out io command 714 . next the actual io issuing means , as the number of held items in the io queue 740 is “ 1 ”, takes out of the io queue 740 the io command 713 , whose sequential position is 1 , to make the number of items held in the io queue 740 “ 0 ”. then it performs physical io upon the magnetic disk 760 indicated by the disk number of the taken - out io command 713 . fig1 is a diagram illustrating the state following the state of fig1 in which the actual io issuing means has taken out one io command address each from the io queues 730 and 740 and performed physical io upon the respectively corresponding magnetic disks 750 and 760 . the state of neither the local chain start nor the io commands is changed . the actual io issuing means successively refers to the io commands 714 and 723 in the io queue 730 , respectively indicated by the io command addresses of sequential positions 1 to 2 ; takes out of the io queue 730 the io command 723 , first found from the io commands having the earliest reserve positions ; successively advances the io command addresses whose sequential positions follow those taken out ; and reduces the number of items held in the io queue 730 by 1 to “ 1 ”. then it performs physical io upon the magnetic disk 750 indicated by the disk number of the taken - out io command 714 . next the actual io issuing means , as the number of held items in the io queue 740 is “ 1 ”, takes out of the io queue 740 the io command 713 , whose sequential position is 1 , to make the number of items held in the io queue 740 by 1 to “ 0 ”. then it performs physical io upon the magnetic disk 760 indicated by the disk number of the taken - out io command 713 . as hitherto described , the present invention has the benefit to provide an access control apparatus which can give equal input / output opportunities to input / output requests from all users by adopting as criterion of priority among input / output processing requests from all users the reserve sequence of reserved input / output requests , held for each individual user , and process the requests efficiently . although the invention has been described in detail above with reference to preferred embodiments thereof , it will be apparent to those skilled in the art that these embodiments have been provided solely for the purpose of illustration , and are in no way to be regarded as limiting the invention . instead , various modifications and substitutions of equivalent techniques will be readily apparent to those skilled in the art upon reading this specification , and such modifications and substitutions are to be regarded as falling within the true scope and spirit of the following claims .