PRODUCT  :  Borland C++                           NUMBER  :  1335
  VERSION  :  3.x
       OS  :  ALL
     DATE  :  October 26, 1993                         PAGE  :  1/4

    TITLE  :  Determining the amount of available extended memory.




            Determining the amount of extended memory present
            =================================================
       The documented INT 15h, 88h may not always accurately return
  the amount of memory present on a PC.  This is a result of the
  method used by memory managers and other applications
  accessing/using extended.  When extended memory is allocated an
  application will usually hook the int 15h and monitor calls to
  function 88H;  the new interrupt handler will only return the
  memory that it is not use by the application.  Most Memory
  Managers will hook interrupt 15h and return a modified result
  when function 88h is called.  This makes this API unreliable.

       The correct and most direct method to get the amount of
  extended memory installed on a given machine is to go thru the
  CMOS.  The CMOS is organized into registers that can be querried
  by performing successive in and out instructions to ports 70H and
  71H.  An out is done to port 70H to tell the CMOS which register
  will be read from or written to. A read or write can then be done
  at port 71H to accomplish the desired read or write.

       The code provided below determines the amount of extended
  memory using the INT 15h API and reading from CMOS directly.
  Running the code on machines with memory managers ( eg. HIMEM.SYS
  ) will result in disimilar values.


  ; ------------;
  ; GETEXT.ASM  ;
  ; ------------;
  .model large, c
  .code
  locals


  ; ***************************************************
  ; *  function to get the amount of extended memory  *
  ; ***************************************************

  COMMENT     @
       - Pass a 1 to the function to retrieve the information thru
        INT 15h,88h.
       - Pass a 0 to the function to retrieve the information thru
       CMOS registers.













  PRODUCT  :  Borland C++                           NUMBER  :  1335
  VERSION  :  3.x
       OS  :  ALL
     DATE  :  October 26, 1993                         PAGE  :  2/4

    TITLE  :  Determing the amount of available extended memory.




       - Returns amount of extended memory ( in K ) found in AX.
  ENDCOMMENT  @


  getext  proc    par:word

          ; get passed word of the stack in cx register
          mov     cx, par

          ; check which method to check for extended memory
          or      cx, cx
          jz      @cmos_check;

  @int15check:

          ; Use the int 15h,88h function
          mov ax, 8800h
          int 15h
          jmp     @exit

  @cmos_check:
          ; Use the cmos data registers
          mov  al, 30h    ; get least significant byte
          out  70h, al
          in   al, 71h
          mov  cl, al

          mov  al, 31h    ; get most significant byte
          out  70h, al
          in   al, 71h
          mov  ch, al

          ; return extended memory in AX
          mov  ax, cx

  @exit:
          ret
          endp

          public  getext
          end















  PRODUCT  :  Borland C++                           NUMBER  :  1335
  VERSION  :  3.x
       OS  :  ALL
     DATE  :  October 26, 1993                         PAGE  :  3/4

    TITLE  :  Determing the amount of available extended memory.




  ;------------;
  ; EXTGET.CPP ;
  ;------------;
  #include <stdio.h>

  #ifdef  __cplusplus
  extern "C" {
  #endif

  unsigned getext( short type );

  #ifdef __cplusplus
  }
  #endif


  int main( void )
  {
       unsigned kilos;

       kilos = getext( 1 );
       printf( "Total extended memory thru' int 15h is %uK\n",
                 kilos );

       kilos = getext( 0 );
       printf("Total extended memory thru' cmos %uK\n", kilos );

       return( 0 );
  }




  To build an .EXE from the two files provided above, use the
  folliwing command:
            BCC -ml -v EXTGET.CPP  GETEXT.ASM

  ( The above command will compiler EXTGET.CPP, invoke TASM.EXE to
  assemble GETEXT.ASM and then call TLINK.EXE to create an
  excutable ).
















  PRODUCT  :  Borland C++                           NUMBER  :  1335
  VERSION  :  3.x
       OS  :  ALL
     DATE  :  October 26, 1993                         PAGE  :  4/4

    TITLE  :  Determing the amount of available extended memory.




  DISCLAIMER: You have the right to use this technical information
  subject to the terms of the No-Nonsense License Statement that
  you received with the Borland product to which this information
  pertains.