Answer OoO, caches, and memory-system questions

You are interviewing for a CPU/DV role. Provide clear explanations (and small worked examples where useful) for the following computer architecture topics: 1) **Out-of-order (OoO) execution basics**: Describe the main structures in an OoO core (e.g., ROB, reservation stations/issue queue, load-store queue), and how an instruction flows through them. 2) **Branch prediction**: - Explain how a **gshare** predictor works (indexing, global history register, counters). - Given a branch outcome, describe how to update the pattern history table (2-bit counters) and the global history register. 3) **Register renaming / RAT tracing**: You are given a short instruction sequence with architectural registers. Explain how to update the rename map table (RAT) and what the final mapping is. (No need for a specific ISA; assume each destination register allocates a new physical register.) 4) **VLIW**: What is VLIW and how does it differ from superscalar OoO designs? Discuss compiler vs hardware complexity. 5) **Cache coherence**: What problem does coherence solve? Compare common protocols (e.g., MSI/MESI/MOESI) at a high level. 6) **Load/store subsystem questions**: - What are the roles of a store buffer and a load-store queue? - What does it mean for loads/stores to be speculative? - For cache tags, when do you use virtual vs physical addresses? 7) **Copy-on-write (COW) after `fork()`**: In an OS using `fork()`, how can parent and child share physical pages initially, and how does the system detect a write that should trigger COW? What exception/fault occurs and what does the handler do? 8) **Cache indexing math**: Given cache capacity, block size, and associativity, show how to compute: - number of sets - index bits - block offset bits - tag bits (assuming a 32-bit address) 9) **VIPT caches and aliasing**: For a virtually indexed, physically tagged cache, explain why aliasing can occur and how designs avoid it (page coloring / size constraints / way prediction etc.). 10) **Async FIFO**: What problem does an asynchronous FIFO solve? Outline the standard gray-code pointer technique and why it’s needed.