Function 49h            Free Allocated Memory

    Frees a block of memory previously allocated by function 48h.

        Entry   AH = 49h
                ES = Segment address of memory to free

        Return  Nothing
                or
                AX = Error code, if CF is set
                     | 07h Memory control blocks destroyed
                     | 09h Invalid memory block address

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    This function returns to DOS the memory that was allocated by
    means of Allocate Memory (function 48h). ES specifies the segment
    address of the block that is being returned; this is the same
    value that function 48h returned in AX.

    DOS returns an error value of 9 (invalid memory block address) if
    a program tries to free memory that was not allocated by function
    48h.

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    Note
    DOS 2.1+ does not coalesce adjacent free blocks when a block is
    freed, only when a block is allocated or resized.