For example, you may start your game as Alice, above ground, who encounters the white rabbit and talks to him. Eventually, you find the rabbit hole and fall down to the room containing "eat me" and "drink me." Consuming these items will presumably have the same effect as in the book.

Likewise, you may interact with the Cheshire Cat, the Mad Hatter and other book characters. Prolonged interaction with the Red Queen will, presumably, prove to be unfortunate. For example, when given the tree shown above as the first argument the predicate should unify the second argument with the list [3,2,7,4,2,5]. [4 marks] (c) Explain why the bfs/2 predicate might benefit from being converted to use difference lists. [2 marks] (d) Implement a new predicate diffbfs/2 which makes use of a difference list to exploit the benefit you identified in part (c). Your predicate should take the same arguments as bfs/2. [6 marks] (e) A friend observes that a clause in diffbfs/2 will need to contain an empty difference list and proposes two possible ways of representing it, either []-[] or A-A. Consider your implementation of diffbfs/2. For each use of an empty difference list, justify your choice and explain what can go wrong using the alternative form. [2 marks Derive upper bounds on the system throughput (i) when the load is very low and (ii) as the load tends to infinity. [5 marks] (d) In what situations may the bounds be particularly imprecise? What can be done to construct tighter bounds for the system throughput? Consider an operating system that uses hardware support for paging to provide virtual memory to applications. (a) (i) Explain how the hardware and operating system support for paging combine to prevent one process from accessing another's memory. [3 marks] Our four event process (a symbol is generated on each edge) is shown graphically together with a two state Markov process for the alphabet fA, B, C, D, Eg in gure 17. We can then solve for the state occupancy using ow equations (this example is trivial).

ess with states fS 1; S2; : : :Sng, with transition probabilities pi(j) being the probability of moving from state Si to state Sj (with the emission of some symbol). First we can dene the entropy of each state in the normal manner: Hi = X j pi(j) log2 pi(j) and then the entropy of the system to be the sum of these individual state entropy values weighted with the state occupancy (calculated from the ow equations):

Pipi(j) log pi(j) (45) (ii) Using the characteristics of the network described above, design a protocol for distributing this information across the network. You should specify the format of your messages and the size of any message fields 4.3 The Source Coding theorem Often we wish to eciently represent the symbols generated by some source. We shall consider encoding the symbols as binary digits. 19 (i) What are the state occupancy probabilities? [1 mark] A colleague suggests replacing the system above with one that provides 80 GB/s memory read bandwidth and main memory access latency of 30 ns. Explain whether you should accept the replacement or not, and why. [4 marks] (c) A creative engineer suggests structuring the TLB so that not all the bits of the presented address need match to result in a hit. Suggest how this might be achieved, and what might be the costs and benefits of doing so. [6 marks] b) What statistical properties of memory access do caches exploit to deliver improved performance? [4 marks] (c) What impact will an operating-system-managed context switch have on cache hit rate? Justify your answer. [4 marks]