Google publishes a guide to its ranking systems. They run continuously, unlike updates, which are discrete changes.
Systems worth knowing
- BERT / MUM, language understanding, for interpreting queries and content.
- Helpful content system, now integrated into core ranking, favouring content made for people.
- Link analysis and PageRank, still part of how importance is judged.
- Reviews system, rewards in-depth review content with first-hand evidence.
- Freshness systems, surface recent content where recency matters.
- Page experience, usability signals.
- Spam detection (SpamBrain), AI-based spam prevention.
Retired systems
Google also lists retired systems, mobile-friendly ranking, page speed as a separate system, Panda and Penguin as standalone systems, because their function has been folded into core ranking.
Alien Road recommends: ignore system names when planning work. They describe how Google organises its own engineering, not a checklist. The practical version is unchanged: is the page genuinely useful, can Google read it, and does anyone credible reference it?