What is an “unused” memory address?

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Reading this page on Commodore 64 memory structure and usage I stumbled across a cell where the table claims that this memory is unused. What exactly does this entail?



Does this mean that if you wanted to put something in that address you can put whatever you want? Confused, and would appreciate all answers.



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    Reading this page on Commodore 64 memory structure and usage I stumbled across a cell where the table claims that this memory is unused. What exactly does this entail?



    Does this mean that if you wanted to put something in that address you can put whatever you want? Confused, and would appreciate all answers.



    picture










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      up vote
      2
      down vote

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      2
      down vote

      favorite











      Reading this page on Commodore 64 memory structure and usage I stumbled across a cell where the table claims that this memory is unused. What exactly does this entail?



      Does this mean that if you wanted to put something in that address you can put whatever you want? Confused, and would appreciate all answers.



      picture










      share|improve this question









      New contributor




      wardialer is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      Reading this page on Commodore 64 memory structure and usage I stumbled across a cell where the table claims that this memory is unused. What exactly does this entail?



      Does this mean that if you wanted to put something in that address you can put whatever you want? Confused, and would appreciate all answers.



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      assembly commodore






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      edited 1 hour ago









      Raffzahn

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          2 Answers
          2






          active

          oldest

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          up vote
          3
          down vote



          accepted










          Back in the day, it meant that present versions of the Commodore BASIC and Kernel did not use those locations, but Commodore said nothing about whether future versions of the ROM might do so. Addresses 251-254, by contrast, were specifically marked as available for user programs and Commodore guaranteed that nothing in present nor future versions of the BASIC nor Kernel would do anything to conflict with such usage.



          Of course, every version of the BASIC and Kernel ROMs that will ever be produced by Commodore, has been produced by now, and any locations which haven't been used by any versions released to date won't be used by any future versions, ever. Back in the day, however, programmers would have had no way of knowing that.



          In official documentation, storage locations which aren't currently used, but which might be used in future, will often be marked "reserved". I don't remember whether Commodore documented the indicated addresses that way. Third-party documentation, especially written after the C64 was discontinued, will be more likely to regard unused locations as "unused" for the reasons indicated above.






          share|improve this answer






















          • It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
            – Dr Sheldon
            53 mins ago











          • @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
            – Raffzahn
            16 mins ago

















          up vote
          2
          down vote














          I stumbled across a cell in the table that claims that the memory address is unused. What exactly does this entail?




          Well, exactly as it's described, it's not used by any of the ROM routines.




          Does this mean that if you wanted to put something in that address you can put whatever you want?




          Exactly - it's one ZP address that can be used in yout programs without causing any conflict with KERNEL or BASIC ROM






          share|improve this answer




















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            2 Answers
            2






            active

            oldest

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            2 Answers
            2






            active

            oldest

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            active

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            up vote
            3
            down vote



            accepted










            Back in the day, it meant that present versions of the Commodore BASIC and Kernel did not use those locations, but Commodore said nothing about whether future versions of the ROM might do so. Addresses 251-254, by contrast, were specifically marked as available for user programs and Commodore guaranteed that nothing in present nor future versions of the BASIC nor Kernel would do anything to conflict with such usage.



            Of course, every version of the BASIC and Kernel ROMs that will ever be produced by Commodore, has been produced by now, and any locations which haven't been used by any versions released to date won't be used by any future versions, ever. Back in the day, however, programmers would have had no way of knowing that.



            In official documentation, storage locations which aren't currently used, but which might be used in future, will often be marked "reserved". I don't remember whether Commodore documented the indicated addresses that way. Third-party documentation, especially written after the C64 was discontinued, will be more likely to regard unused locations as "unused" for the reasons indicated above.






            share|improve this answer






















            • It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
              – Dr Sheldon
              53 mins ago











            • @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
              – Raffzahn
              16 mins ago














            up vote
            3
            down vote



            accepted










            Back in the day, it meant that present versions of the Commodore BASIC and Kernel did not use those locations, but Commodore said nothing about whether future versions of the ROM might do so. Addresses 251-254, by contrast, were specifically marked as available for user programs and Commodore guaranteed that nothing in present nor future versions of the BASIC nor Kernel would do anything to conflict with such usage.



            Of course, every version of the BASIC and Kernel ROMs that will ever be produced by Commodore, has been produced by now, and any locations which haven't been used by any versions released to date won't be used by any future versions, ever. Back in the day, however, programmers would have had no way of knowing that.



            In official documentation, storage locations which aren't currently used, but which might be used in future, will often be marked "reserved". I don't remember whether Commodore documented the indicated addresses that way. Third-party documentation, especially written after the C64 was discontinued, will be more likely to regard unused locations as "unused" for the reasons indicated above.






            share|improve this answer






















            • It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
              – Dr Sheldon
              53 mins ago











            • @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
              – Raffzahn
              16 mins ago












            up vote
            3
            down vote



            accepted







            up vote
            3
            down vote



            accepted






            Back in the day, it meant that present versions of the Commodore BASIC and Kernel did not use those locations, but Commodore said nothing about whether future versions of the ROM might do so. Addresses 251-254, by contrast, were specifically marked as available for user programs and Commodore guaranteed that nothing in present nor future versions of the BASIC nor Kernel would do anything to conflict with such usage.



            Of course, every version of the BASIC and Kernel ROMs that will ever be produced by Commodore, has been produced by now, and any locations which haven't been used by any versions released to date won't be used by any future versions, ever. Back in the day, however, programmers would have had no way of knowing that.



            In official documentation, storage locations which aren't currently used, but which might be used in future, will often be marked "reserved". I don't remember whether Commodore documented the indicated addresses that way. Third-party documentation, especially written after the C64 was discontinued, will be more likely to regard unused locations as "unused" for the reasons indicated above.






            share|improve this answer














            Back in the day, it meant that present versions of the Commodore BASIC and Kernel did not use those locations, but Commodore said nothing about whether future versions of the ROM might do so. Addresses 251-254, by contrast, were specifically marked as available for user programs and Commodore guaranteed that nothing in present nor future versions of the BASIC nor Kernel would do anything to conflict with such usage.



            Of course, every version of the BASIC and Kernel ROMs that will ever be produced by Commodore, has been produced by now, and any locations which haven't been used by any versions released to date won't be used by any future versions, ever. Back in the day, however, programmers would have had no way of knowing that.



            In official documentation, storage locations which aren't currently used, but which might be used in future, will often be marked "reserved". I don't remember whether Commodore documented the indicated addresses that way. Third-party documentation, especially written after the C64 was discontinued, will be more likely to regard unused locations as "unused" for the reasons indicated above.







            share|improve this answer














            share|improve this answer



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            edited 24 mins ago

























            answered 1 hour ago









            supercat

            5,859633




            5,859633











            • It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
              – Dr Sheldon
              53 mins ago











            • @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
              – Raffzahn
              16 mins ago
















            • It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
              – Dr Sheldon
              53 mins ago











            • @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
              – Raffzahn
              16 mins ago















            It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
            – Dr Sheldon
            53 mins ago





            It might be worth noting that today the word "reserved" is more commonly used for this purpose than "unused". +1
            – Dr Sheldon
            53 mins ago













            @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
            – Raffzahn
            16 mins ago




            @DrSheldon Not realy, as Reserved means that this location might be used at some future point and should not be used by application program. Ir one would replace unused by reserved, then there would be no usable memory within all of the 64 LiB :))
            – Raffzahn
            16 mins ago










            up vote
            2
            down vote














            I stumbled across a cell in the table that claims that the memory address is unused. What exactly does this entail?




            Well, exactly as it's described, it's not used by any of the ROM routines.




            Does this mean that if you wanted to put something in that address you can put whatever you want?




            Exactly - it's one ZP address that can be used in yout programs without causing any conflict with KERNEL or BASIC ROM






            share|improve this answer
























              up vote
              2
              down vote














              I stumbled across a cell in the table that claims that the memory address is unused. What exactly does this entail?




              Well, exactly as it's described, it's not used by any of the ROM routines.




              Does this mean that if you wanted to put something in that address you can put whatever you want?




              Exactly - it's one ZP address that can be used in yout programs without causing any conflict with KERNEL or BASIC ROM






              share|improve this answer






















                up vote
                2
                down vote










                up vote
                2
                down vote










                I stumbled across a cell in the table that claims that the memory address is unused. What exactly does this entail?




                Well, exactly as it's described, it's not used by any of the ROM routines.




                Does this mean that if you wanted to put something in that address you can put whatever you want?




                Exactly - it's one ZP address that can be used in yout programs without causing any conflict with KERNEL or BASIC ROM






                share|improve this answer













                I stumbled across a cell in the table that claims that the memory address is unused. What exactly does this entail?




                Well, exactly as it's described, it's not used by any of the ROM routines.




                Does this mean that if you wanted to put something in that address you can put whatever you want?




                Exactly - it's one ZP address that can be used in yout programs without causing any conflict with KERNEL or BASIC ROM







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered 1 hour ago









                Raffzahn

                37.4k483149




                37.4k483149




















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