Assume there exists a Buddy System memory allocator and its initial buffer is $1024$ blocks. The following memory chunks are allocated and released: Please draw the following steps $(1)-(6)$ and explain how a buddy system allocates$/$deallocates memory space.

$(1)$ A $=$ allocate$(256)$

$(2)$ B $=$ allocate$(128)$

$(3)$ C $=$ allocate$(256)$

$(4)$ D $=$ allocate$(256)$

$(5)$ free$($B$),$

$(6)$ free$($C$).$