referring now to the drawings , wherein like reference numerals designate identical or corresponding parts throughout the several views , and more particularly to fig3 thereof , a block diagram of a data processing system according to the present invention is illustrated . in fig3 a main memory 34 is coupled with a system bus ( s - bus ) 30 . an input / output processor ( iop ) 33 and a central processing unit ( cpu ) are connected to the system bus 30 . the central processing unit cpu 31 includes a high speed memory 51 . the high speed memory 51 is used as a general register ( gr ) and as a scratchpad memory ( spm ). an arithmetic and a logic unit ( alu ) 54 is connected to the high speed memory 51 by way of the d - bus 59 , the a - bus 58 , and a register ( reg ) 55 and performs various arithmetic and logical operations . the register reg 55 is connected to the d - bus 59 and the arithmetic and logic unit 54 and temporarily stores the results before or after an operation of the arithmetic and logic unit 54 . the a - bus 58 is connected to the system bus 30 by way of a driver 56 . an instruction code from the main memory 34 is loaded into an instruction register ( ir ) 53 through the system bus 30 , a receiver 57 , and the a - bus 58 . an address register ( ar ) 52 stores an address of the high speed memory 51 . control memory ( cs ) 62 stores a microprogram . the microinstruction register ( μir ) 63 stores microinstructions from the μir 63 . the microprogram sequencer ( μseq ) 64 includes a microprogram address register ( μar ) 65 , an adder ciruit (+ 1 ) 66 , and an address selecter ( sel ) 67 . the microprogram sequencer μseq 64 forms a real address based on the microprogram stored in the cs 62 . the cs 62 is connected to the adder 66 of the microprogram sequencer 64 which is connected to the instruction register ir 53 and to the microinstruction register μir 63 , and selects one address in accordance with the microprogram control . a device similar to the microprogram sequencer μseq 64 is described in a manual issued by advanced micro devices corporation , microprogram sequencer am 2911 . the central processing unit 31 includes a dynamic address translator ( dat ) 36 . the dynamic address translator 36 includes a memory which stores the page table . the details of the dynamic address translator 36 will be described with reference to fig4 . in fig4 the lower 12 bits ( bits 0 - 11 ) of the virtual address correspond to the lower 12 bits of the real address . the upper 12 bits ( i . e . ), bits 12 - 23 shown in fig4 ); of the virtual address designate the memory address of the page table ( pt - ram ) 37 . the output of the page table pt - ram 37 forms not only the upper bits ( bits 12 - 21 ) of the real address but also acts as an input to a driver 41 . the output of the driver 41 is connected to the system bus 30 and controls a microprogram of the central processing unit 31 to enable the reading of the output of the page table pt - ram 37 under the control of an internal signal of the central processing unit 31 . the microprogram of the central processing unit 31 can write a desired real address in the page table pt - ram 37 to which the a - bus 58 is connected . the page table pt - ram 37 may be formed from a random access memory of 4096 words . referring now to fig5 the format of a data word used in the page table pt - ram 37 in fig4 is illustrated . each word of the page table pt - ram 37 includes upper bits of the real address ( i . e ., bits 20 - 31 shown in fig5 ) and control bits v , r and c . bit v is a validity bit to indicate that the upper bit of the real address included in the words should be effective . bit r is a reference bit to be set to &# 34 ; 1 &# 34 ; each time the word is accessed . bit c is a change bit to be set to &# 34 ; 1 &# 34 ; each time the word is accessed for writing . referring back to fig4 the operation of the dynamic address translater 36 will be explained when the central processing unit 31 accesses the memory by designating a virtual address . bits 12 - 23 of the virtual address given from central processing unit 31 address the page table pt - ram 37 . the output of the page table pt - ram 37 becomes bits 12 - 21 of the real address . bits 0 - 11 of the real address use bits 0 - 11 of the virtual address . the real address obtained in the manner as explained above is transferred to the main memory 34 to address it through the d - bus 59 shown in fig3 . in this embodiment , the input / output processor 33 also addresses the main memory 34 with the real address . the central processing unit translates the virtual address preliminarily into the real address by means of software when it gives a channel program to the input / output processor . it is apparent from fig4 that the dynamic address translator 36 is simplified . almost all of the dynamic address translator 36 is in page table pt - ram 37 . the size of the page table pt - ram 37 is twice the capacity of the memories 22 and 25 as in the translation look - aside buffer 13 of the prior art using a memory element of 1k words . thus the dynamic address translator 36 can be constructed of a hardware equivalent of the translation look - aside buffer 13 of the prior art . dynamic address translator 12 of the prior art includes not only the translation look - aside buffer 13 but also an adder and a register for address calculation to access page table 15 in the main memory , an access control circuit for the main memory , and a sequential control circuit etc . as a result of locating the page table in the dynamic address translation and not in the main memory , it is unnecessary to prepare the above mentioned circuits and it is only necessary to utilize one half of the hardware . in the near feature , when a high speed static random access memory having a large capacity of 4k words times 4 bits is available , it will further enlarge the merits of the present invention because one memory 22 in the translation look - aside buffer in fig2 is similar in size to the page table pr - ram 37 in fig4 . now referring to fig6 a pth instruction i . e ., an instruction to modify the page table 37 , will be explained as follows . the format of the pth instruction and the usage of it by a general register are shown in fig6 . the pth instruction provides the means by which the operating system defines and revises the page table 37 within the dynamic address translator 36 . when it is necessary to utilize the central processing unit , it is convenient to address it via software using the page table if the necessary hardware is available to write such contents as to translate the same real address to the virtual address within the real address of the page table pt - ram 37 . the pth instruction includes a portion serving as an instruction code ( op ), another portion to indicate the general register , and a portion ( c ) for variation of itself . with respect to the pth instruction , a general register grn stores the virtual address and the general register stores the upper 16 bits of a word of the page table . in the present embodiment of the present invention , the virtual address is stored in the general register . it is possible to design an instruction format to designate a virtual address by a portion of the instruction word . this variation of the pth instruction by the c bit is as follows . in the following explanation each word in the page table is referred to as a page table entry ( pte ). write the upper 16 bits of the general register grn + 1 into the page table entry pte designated by the virtual address in the general register grn . each entry of the page table pt is formed by 13 bits of information . in the present embodiment the 31st bit , the 30th bit , and the 16th bit are extended bits , i . e ., bits which are not actually entered or stored in the page table . set the page table entry designated by the virtual address in the general register grn to the upper 16 bits of the general register grn + 1 . reset the r bit of the page table entry designated by the virtual address in the general register grn to zero . fig7 is a flow chart of an embodiment of the page table entry instruction . the operation of the central processing unit thus constructed will now be described referring to fig7 . the central processing unit 31 reads the software instruction using the main memory 34 . the instruction read is set into the instruction register 53 through the a - bus 58 from the system bus 30 . the instruction code op set in the instruction register 53 is decoded by ) seq 64 . when the contents of the instruction code op is the pth instruction , the control is removed to the ) seq 64 , where the microprogram routine for implementing the pth instruction is performed . in other words , the variation of the pth instruction is judged by the c bit . the head address for processing the microprogram corresponds to the variation in the control bit c is determined . when the control bit is ( c - 1 ), the microprogram processing routine is as follows . the contents of the general register grn are given as the virtual address , and the contents of the general register grn + 1 cause the page table pt - ram 37 to write through the d - bus 59 . the high speed memory spm 51 is addressed by the contents of the address register ar 52 , and the contents obtained ( the page number , the displacement ) is sent through the d - bus 59 , the arithmetic and logic unit alu 54 , and the a - bus 58 to a virtual address register ( var ) 42 . at the same time , the high speed memory spm ( grn + 1 51 is addressed in accordance with the addition of + 1 to the contents of the address register ar 52 and the one word of the page table is sent through the d - bus 59 , the arithmetic and logic unit alu 54 , and the a - bus 58 to the register reg 55 . the one word of the page table pt in the register reg 55 is written in the page table pt - ram 37 in accordance with the upper bits of the virtual address in the virtual address register var 41 . when the control bit is ( c = 2 ), the microprogram processing routine is as follows . the contents of the general register grn are given as the virtual address . the page table entry pte indicated by bits 23 - 12 of the general register grn is read from the page table pt - ram 37 and is loaded into the upper 16 bits of the general register grn + 1 . that is to say , the high speed memory spm 51 is addressed by the contents of the address register ar 52 , and the contents thus obtained ( the page number , the displacement ) are sent through the d - bus 59 , the arithmetic and logic unit alu 54 , and a - bus to the virtual address register var 41 . the page table pt - ram 37 is addressed by the page number ( bits 12 - 23 ) of the virtual address register var , and the contents of the page table pt - ram 37 are obtained and are transferred through the d - bus 59 , the arithmetic and logic unit alu 54 , and the a - bus to the high speed memory spm 51 ( grn + 1 ). at the same time , to the contents of the address register ar 52 is added + 1 . when the control bit is ( c = 3 ), the microprogram procesing routine is as follows . the page table entry pte indicated by bits 23 - 12 of the general register grn is read from the page table pt - ram 37 and is loaded into the arithmetic and logic unit alu 54 . bit 18 ( the r bit ) of the arithmetic and logic unit alu 54 is reset , and the real address is written in the same portion of the page table pt - ram 37 . it is clear from the foregoing , in the address conversion system according to the present invention , the hardware of the dynamic address translator dat is simplified and can be relatively small . the time necessary for address translation is made shorter , because the address for translating is accessed in the main memory . obviously , numerous modifications and variations of the present invention are possible in light of the above teachings . it is therefore to be understood that within the scope of the appended claims , the invention may be practiced otherwise than as specifically described herein .