Directory Protocol Evolution & Taxonomy

From Full Bit Vector → Limited Pointer → Clustered/Hierarchical → Dorado (3-pronged simultaneous improvement)

_NB (1980s) ✓ Precise tracking ✗ O(N²) storage Limited Pointer Dir_nB (n≪N) ✓ Low storage ✗ Broadcast on overflow Storage-Optimized Branch Cuckoo Dir [16]Hash table org↑ insert latency Bloom [67][70]ProbabilisticFalse positives Overflow into LLCWayPoint[10], TinyDir[57], ZeroDEV[29]↑ eviction cost, less LLC capacity Latency-Optimized Branch Home Deleg. [11][50]pt-to-pt direct Net Optim. [26]VTC multicast Prediction [24][46] Hierarchical / Tree-based Hier. Dir [21][38]Multi-level Tree Coh. [43][52]Write: up→down Many-Sharer Solutions SCD[55], WayC[64], PoolDir[56] Each: complex or limited 🐟 Dorado (ISCA 2026) TLH (Latency+Traffic) + Dynamic Apportioning (Storage) + SetOverflow (Many-Sharer) "First protocol to simultaneously address latency, traffic, AND storage"