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─────PWB Extensions─────────────────────────────────────────────────────────
 
  Syntax:  void fpbToVM( char far *fpb, long va, unsigned count );
           long VMAlloc( long count );
           void VMFree ( long vm );
           void VMTofpb( long va, char far *fpb, unsigned count );
           long VMSize ( long vm );
 
  Returns: VMAlloc returns a virtual address.
           VMSize returns the size in bytes of a memory block in VM.
 
  See:     Falloc, Fdalloc
 
     The virtual-memory functions allocate and manage virtual memory.
     Unlike normal memory, virtual memory is not limited to 64K blocks.
     If there is insufficient actual memory, portions of virtual memory
     are automatically swapped to disk. Virtual memory is used for
     handling very large blocks of data, such as help files.
 
     VMAlloc allocates virtual memory. The <count> specifies the number
     of bytes allocated. The value returned is the start of the
     allocated virtual memory. Allocated blocks must be accessed as
     offsets from this value.
 
     The fpbToVM function copies a sequence of bytes into virtual memory
     from <fpb>, a far pointer to a buffer of data. Normally the buffer
     is a block of memory allocated with Falloc, although static memory
     can also be used. The <va>, virtual address, is the offset of the
     virtual memory block to which the data is copied. The <count> is
     the length in bytes of the copied block.
 
     VMTofpb copies bytes from virtual memory to a <fpb>, a far pointer
     to a destination buffer. The <va>, virtual address, is the offset
     of the virtual memory block from which the data is copied. The
     <count> is the length in bytes of the copied block.
 
     VMFree frees a <vm>, virtual memory, previously allocated by
     VMAlloc.
 
     VMSize returns the size of a virtual memory block.
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