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INT 21 - Phar Lap 386/DOS-Extender VMM - GET MEMORY STATISTICS
        AX = 2520h
        DS:EDX -> pointer to buffer at least 100 bytes in size (see below)
        BL = 0 (don't reset VM stats), 1 (reset VM stats)
Return: carry flag clear

Format of VM stats buffer:
Offset  Size    Description
 00h    DWORD   VM status
                0001h VM subsystem is present
                0000h VM not present
 04h    DWORD   "nconvpg" number of conventional memory pages available
 08h    DWORD   "nbimpg" number of Compaq built-in memory pages available
 0Ch    DWORD   "nextpg" total number of extended memory pages
 10h    DWORD   "extlim" extender memory pages limit
 14h    DWORD   "aphyspg" number of physical memory pages allocated to appl
 18h    DWORD   "alockpg" number of locked pages owned by application
 1Ch    DWORD   "sysphyspg" number physical memory pages allocated to system
 20h    DWORD   "nfreepg" number of free physical pages; approx if EMS VCPI
 24h    DWORD   linear address of beginning of application address space
 28h    DWORD   linear address of end of application address space
 2Ch    DWORD   number of seconds since last time VM stats were reset
 30h    DWORD   number of page faults since last time
 34h    DWORD   number of pages written to swap file since last time
 38h    DWORD   number of reclaimed pages (page faults on swapped pages)
 3Ch    DWORD   number of virtual pages allocated to the application
 40h    DWORD   size in pages of swap file
 44h    DWORD   number of system pages allocated with EMS calls
 48h    DWORD   minimum number of conventional memory pages
 4Ch    DWORD   maximum size in bytes to which swap file can be increased
 50h    DWORD   "vmflags" bit 0 = 1 if page fault in progress
 54h 16 BYTEs   reserved for future expansion (set to zero)