Instruction Level Parallelism (ILP)

Lecture 21 investigates Instruction Level Parallelism (ILP) and advanced processor microarchitectures capable of achieving CPI < 1 (superscalar execution). The lecture examines static ILP techniques (loop unrolling, software pipelining) and dynamic hardware ILP mechanisms. Students explore dynamic instruction scheduling, out-of-order execution using Tomasulo's algorithm, reservation stations, and reorder buffers (ROB) for in-order retirement. The lecture analyzes branch prediction strategies: static prediction (predict-taken, predict-not-taken) and dynamic 2-bit saturating branch history tables, evaluating speculative execution throughput. In this lecture, students investigate the structural organization, hardware interfaces, and microarchitectural mechanisms of modern computing systems. Through rigorous mathematical formulas and register transfer notation, the lesson clarifies quantitative performance tradeoffs and hardware execution cycles. Special attention is given to clock cycle time, CPI metrics, datapath timing constraints, and control signal generation. Mastering these hardware principles allows learners to evaluate processor throughput, identify execution bottlenecks, and design optimized computer systems. Analytical exercises and solved examples further assist students preparing for Virtual University midterm and final term exams. The curriculum systematically connects instruction set architecture concepts with silicon microarchitecture and assembly-level implementation details. Reviewing the accompanying lecture handouts and RTL diagrams reinforces understanding of processor datapath and control unit cooperation. Consistent hands-on analysis of instruction encoding formats and timing diagrams ensures comprehensive preparation for assessments. The lesson contrasts single-cycle, multi-cycle, and pipelined datapath organizations to highlight execution throughput advantages. Detailed timing traces illustrate how control signals orchestrate register transfers, bus gating, and memory access states. Students examine the foundational trade-offs between hardware control simplicity and compiler-driven software instruction scheduling. Practical architectural case studies emphasize the historical evolution from accumulator machines to modern load-store RISC architectures. Hardware-software co-design principles are analyzed to demonstrate how compiler optimizations leverage underlying microprocessor structures. The module integrates authoritative insights from Vincent P. Heuring, Harry F. Jordan, John L. Hennessy, and David A. Patterson. Careful consideration is given to electrical propagation delays, setup and hold times, and critical path timing analysis.