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; at the data area:

     MEMORY_SIZE     dd 0
     mem_map         dd 0

;.. later on; in the "function" area:

     ; INT 15h, E820h to get memory map and determine memory.
     ;--------------------------------------------------------
     mem_e820:
          pusha
          mov     ebx, 0                              ; EBX clear
          mov     ebp, ebx                            ; EBP clear
          mov     edi, mem_map+4                      ; ES:DI buffer to read info into

     .again
          mov     eax, 0x0e820                        ; EAX service no
          mov     edx, 0x534d4150                     ; EDX with 'SMAP'
          mov     ecx, 0x14                           ; 20 bytes to read
          int     15h
          jc      .end                                ; If carry then END

          cmp     eax, 0x534d4150                     ; If EAX!=SMAP
          jne     .end                                ; then END

          mov     dword eax, [di+8]                   ; else get the length of segment
          add     ebp, eax                            ; add it to EBP
          add     edi, 20+4
          inc     dword [mem_map]
          cmp     ebx, 0                              ; If EBX==0 then END
          jne     .again                              ; Else continue

     .end
          mov     dword [MEMORY_SIZE], ebp            ; Store the result in the variable
          popa                                        ; restore all registers
          mov     eax, [MEMORY_SIZE]
          ret                                         ; Return.

; .. and later; when i call the function:

     ; Determine all installed memory and make a memory map.
     ;-------------------------------------------------------
     MemCheck:
          mov     si, msgCheckMem                     ; Print
          mov     bl, 07h                             ; lightgrey
          call    DisplayMessage                      ; message.

          call    mem_e820                            ; use INT 15h,E820
          jnc     mem_done

          mov     si, msgMemFailed                    ; Print
          mov     bl, 04h                             ; red
          call    DisplayMessage                      ; message.

          mov     si, msgFailure                      ; Print reboot msg and wait to reboot
          mov     bl, 04h                             ; red
          call    DisplayMessage                      ; message.

          mov     ah, 0x00
          int     0x16                                ; Wait for keypress

          db      0EAh                                ; Machinecode, jmp to FFFF:0000 (reboot)
          dw      0000h
          dw      0FFFFh

     mem_done:                                        ; Memory check complete
          cmp     eax,1024*1024*15                    ; At least 16MB should be present
          jl      .needmore
          jmp     A20

     .needmore:
          mov     si, msgMemLess                      ; Print
          mov     bl, 04h                             ; red
          call    DisplayMessage                      ; message.

          mov     si, msgFailure                      ; Print reboot msg and wait to reboot
          mov     bl, 04h                             ; red
          call    DisplayMessage                      ; message.

          mov     ah, 0x00
          int     0x16                                ; Wait for keypress

          db      0EAh                                ; Machinecode, jmp to FFFF:0000 (reboot)
          dw      0000h
          dw      0FFFFh