Cache Coherence: Basics and Protocols

This lecture by the instructor covers the fundamental concepts of cache coherence in multiprocessor systems, focusing on the challenges of sharing data among multiple CPUs. It explains the incoherence problem that arises due to shared data and presents solutions like the Single Writer, Multiple Reader (SWMR) policy. The lecture delves into basic coherence mechanisms such as the Valid/Invalid protocol and the MSI protocol, detailing their operations and state transitions. It also introduces more advanced concepts like the MESI protocol and directory-based coherence. Through examples and exercises, the lecture illustrates the traffic patterns and limitations of different coherence protocols, emphasizing the importance of maintaining a consistent view of memory across parallel processors.