1. What operations does malloc() need to do to make a new allocation?

    Most implementations will do the following. One, search for a free 
    adequately sized contiguous block of memory in the heap. Two, 
    initialize a header. Three, return the memory address at the start 
    of your allocated block of memory.  

2. What operations does free() need to do to free an allocation()?

    At minimum, the function will free the relevant chunk of memory by 
    modifying the header. Beyond this you may choose to have additional 
    optimizations such as coalescing.

3. What aspects of malloc are up to specific implementations?

    A LOT! Header metadata, allocation strategies, memory alignment/padding
    , etc. Each implementation of malloc weighs different tradeoffs between
    space and time complexity.