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DOS interrupt (read only) with NT

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  • DOS interrupt (read only) with NT

    I don't have Windows NT. Will the following
    work in a PBDOS program running under NT without
    the user having "special priveleges"?
    Code:
    '' DISKFREE
    ! mov  AX,&H3600      ; function 36h, get drive info
    ! mov  DX,DriveNum    ; requested drive
    ! int  &H21           ; call DOS
    Politically incorrect signatures about immigration patriots are forbidden. Googling “immigration patriots” is forbidden. Thinking about Googling ... well, don’t even think about it.

  • #2
    Theoretically: It still works.
    Practically : No support for modern large drives. Reading the result with
    drives > 2 Gb is unreliable....
    (Using the Win API functions is really the best solution)

    ------------------
    Peter.
    mailto[email protected][email protected]</A>
    Regards,
    Peter

    Comment


    • #3
      "Reading the result with drives > 2 Gb is unreliable."

      One limitation is that since DOS gives the answer
      as a double word, the largest number of gigabytes
      it can measure is

      2^32 / 1024^3 = 4

      So if you have more than 4 gigabytes free, it
      can't measure it (maybe it wraps through 0).

      Otherwise is it reliable with 95/98 and
      with NT/2000/XP ?

      [This message has been edited by Mark Hunter (edited December 15, 2001).]
      Politically incorrect signatures about immigration patriots are forbidden. Googling “immigration patriots” is forbidden. Thinking about Googling ... well, don’t even think about it.

      Comment


      • #4
        No, definitely not at all in my experience.

        For example, the following code reports around 970Mb free on most of drives under Win2K (aka, NT5) when there is, for example, 3.86Gb free.

        Ditto for network drives, and can give VERY unusual results for CDROM drives if the DOS CDROM drivers are not enabled in CONFIG.NT and AUTOEXEC.NT. On my systen here, it reports the CDROM drive as having 484Gb free when there is no disc in the drive!
        Code:
        function FreeSpace&&(Drive%) local public
                reg 4, Drive%
                reg 1, &H3600
                call interrupt &H21
                function = cqud(bits??(reg(2)) * bits??(reg(3)) * bits??(reg(1)))
        end function
        I filled one one NTFS drive so that there was 1.76Gb free and it still reported 970Mb.

        The moral: don't read all you believe from that interrupt.

        ------------------
        Lance
        PowerBASIC Support
        mailto:[email protected][email protected]</A>
        Lance
        mailto:[email protected]

        Comment


        • #5
          michael mattias wrote in http://www.powerbasic.com/support/pb...read.php?t=516

          "you cannot access the winapi from a dos program,
          but you can access the winapi from a windows program
          which is shelled from your pb/dos program."

          so the program could get the free disk space by shelling
          to a pbcc executable that writes the number to a file,
          and then reading the file.

          but it's a bit complicated if it's to work for all
          versions of windows. from the pbcc help-file for
          pbcc's function diskfree (slightly paraphrased):

          "in 32-bit windows, a maximum of two gigabytes is
          returned, even if more free space is available. in
          some early versions of windows 95, diskfree may
          return a negative value for drives or partitions
          larger than two gigabytes.

          "the getdiskfreespaceex api retrieves the free space
          on a disk. however this api is not available in
          early versions of windows 95 (pre-osr2). it is
          available on all versions of windows that support
          fat32 or ntfs file systems."
          Politically incorrect signatures about immigration patriots are forbidden. Googling “immigration patriots” is forbidden. Thinking about Googling ... well, don’t even think about it.

          Comment


          • #6
            While we're on this topic, Is there any way to access AH
            from PowerBASIC?

            I am playing around with some of the stuff on Ralf Brown's
            interrupt list, using REG, and CALL INTERRUPT, but I want
            to go further.



            ------------------
            Amos
            mailto:[email protected][email protected]</A>

            Comment


            • #7
              Ok, nevermind, I just looked at Lance's example, and figured out
              what I am messing up....

              ------------------
              Amos
              mailto:[email protected][email protected]</A>

              [This message has been edited by Amos Vryhof (edited December 16, 2001).]

              Comment


              • #8
                Would that be casting to unsigned?

                ------------------
                Lance
                PowerBASIC Support
                mailto:[email protected][email protected]</A>
                Lance
                mailto:[email protected]

                Comment


                • #9
                  Well, in Ralph Brown's interrupt list, the sub function is
                  AH=36h, and it seems to work fine with how you stuffed 3600h into
                  AX....so I'm guessing, there is some kind of coincidence here...

                  Hope I'm right.

                  ------------------
                  Amos
                  mailto:[email protected][email protected]</A>

                  Comment


                  • #10
                    AX is a 16-bit register, which can be addressed as two 8-bit registers,
                    AH and AL. Setting AX = &H3600 is the same as setting AH = &H36 and AL = 0.

                    ------------------
                    Tom Hanlin
                    PowerBASIC Staff

                    Comment


                    • #11
                      Hmm...interesting....looks like I need to look up more information
                      on registers....maybe that will help. Unfortunately, in school,
                      I never learned x86 Assembly....I learned MIPS

                      ------------------
                      Amos
                      mailto:[email protected][email protected]</A>

                      Comment

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