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  Return
 
    LongInt    Size in bytes of largest block available for allocation
               (MaxAvail) or of total free space in heap (MemAvail)
 
  Description
 
    The MaxAvail function returns the size of the largest heap block
    available for allocation. The largest block is either the largest
    disposed variable in the free list or the size of the remaining
    free heap.
 
    The MemAvail function returns the total size in bytes of all the
    free space on the heap. The total includes both the deallocated
    blocks in the free list and the unallocated space on the heap.
 
    QuickPascal uses a free list to manage areas returned to the heap
    by the procedures Dispose and FreeMem. The free list is a list of
    pointers that grows downward (toward 0) from the top of the heap
    segment. FreePtr, defined in the System unit, points to the free
    list. Deallocated areas below the current top of the heap are kept
    in the free list. The procedures GetMem and New allocate from the
    free list before taking any new memory from the heap.
 
    HeapPtr, a pointer variable defined in the System unit, always
    points to the top of the heap. Allocation causes the heap to grow
    upward (toward FFFF) from the bottom of the heap segment. The
    unallocated part of the heap includes memory above the top of the
    heap, as well as the blocks in the free list.
 
    MaxAvail returns either the size of the largest block in the free
    list or the size of the unallocated heap above the address in
    HeapPtr, whichever is greater. MemAvail returns the sum of the
    block sizes in the free list and the size of the unallocated heap
    above HeapPtr.
 
    If MaxAvail returns a value smaller than the memory needed, the
    memory cannot be allocated. To check that sufficient memory is
    available, compare the return value of MaxAvail with the return
    from the SizeOf function. Call the Dispose, FreeMem, or Release
    procedures to free heap space.
 
    The value returned by MemAvail does not necessarily give the size
    of a variable that can be allocated, because the free space may be
    fragmented. Call MaxAvail to find the size of the largest available
    block.
 
    The {$M} compiler directive and FreeMin, defined in the System unit,
    both affect the values returned by MaxAvail and MemAvail.