Two bit saturating counters
2 bits scheme used in:
- Alpha 21164
- UltraSparc
- Pentium
- Power PC 604 and 620 with variations
- MIPS R10000 etc...
PA-8000 uses a variation
- Majority of the last 3 outcomes (no need to update; just a shift register)
Why not 3 bit (8 states) saturating counters?
- Performance studies show it’s not worthwhile