
660 CHAPTER 8 Directory-Based Cache Coherence
buses and rings that are discussed in Chapters 5 and 6. We have also been intro-
duced to hierarchical directory schemes in this chapter. This section describes these
hierarchical approaches to coherence further. Although hierarchical ring-based
snooping has been used in commercial systems (e.g., in the Kendall Square Research
KSR1 [Frank, Burkhardt, and Rothnie 1993]) as well as research prototypes (e.g., in
the University of Toronto's Hector system [Vranesic et al. 1991; Farkas, Vranesic,
and Stumm 1992]), and hierarchical directories have been studied in academic
research, these approaches hav ...