Google’s new guide to ranking systems will inform you about which systems Google uses to rank search results and which are obsolete.
Google also introduces new terminology in its latest guide, distinguishing between “ranking systems” and “updates” to rankings.
A system such as RankBrain is constantly running in the background. An update, on the other hand, refers to a one-time change in the ranking system. For example, the useful content system is always running in the background when Google provides search results, although it may receive updates to improve its performance.
Core algorithm updates and spam updates are other examples of one-time changes to ranking systems.

Now that we’ve figured out Google’s new terminology, let’s take a look at the highlights in Google’s guide to ranking systems.
Google’s current ranking systems
Here’s an alphabetical list of Google’s current ranking systems.
BERT : Short for bidirectional coders from Transformers, BERT allows Google to understand how combinations of words can express different meanings and intentions.
Crisis Information Systems . Google has systems to provide certain sets of information during crises, such as SOS alerts when searching for natural disasters.
Deduplication systems.

Google search engines try to avoid duplicate or nearly duplicate web pages.
Exact domain matching system : a system that ensures that Google does not overly trust websites with domain names that exactly match the query.
Freshness systems : a system designed to display fresher content for queries where this would be expected.

Useful Content System : a system designed to make people better able to see original, useful content rather than content created primarily to get traffic from search engines.
Link analysis and PageRank systems : systems that determine what pages are about and which ones might be most useful in response to a query, based on how pages link to each other.
Local News Systems : a system that displays local news sources when they are relevant to a query.
MUM : Short for Multitask Unified Model, MUM is an artificial intelligence system capable of understanding and generating language. It improves selective excerpts and is not used for general ranking.

Neural Mapping: A system that helps Google understand representations of concepts in queries and pages and match them to each other.
Original content systems : a system that helps Google show original content prominently in search results, including original reports, before those who simply cite it.
Removal-based demotion systems : systems that demote websites with high volume of content removal requests.

Page Perception System : a system that evaluates various criteria to determine if a web page provides good user interaction.
Click-through ranking system : an artificial intelligence system that Google uses to identify individual sections or “snippets” of a web page to better understand how relevant a page is to a search.
Product Review System : a system that rewards high-quality product reviews written by expert authors with insightful analysis and original research.
RankBrain : an artificial intelligence system that helps Google understand how words are related to concepts. Allows Google to return results that do not contain the exact words used in the query.
Robust Information Systems . Google has several systems for displaying reliable information, such as boosting authoritative pages, downgrading low-quality content, and encouraging quality journalism.

Site diversity system : a system that prevents Google from displaying more than two lists of web pages from the same site in the top search results.
Spam detection systems : a system that handles content and actions that violate Google’s spam policy.

Obsolete Google ranking systems
The following systems are marked for historical purposes. They have been incorporated into other systems or have become part of Google’s main ranking system.
Hummingbird : A significant improvement to Google’s ranking system, launched in 2013.
Mobile-friendly ranking system : a system that favors content that displays better on mobile devices. It has since been incorporated into Google’s page interaction system.
Page speed system : a system introduced in 2018 that favored content that loaded quickly on mobile devices. It has since been incorporated into Google’s page interaction system.
Panda : a system introduced in 2011 that favored high-quality and original content. In 2015, it became part of Google’s main ranking system.
Penguin system : a system introduced in 2012 that downgraded websites with link building techniques for spam.
Secure Site System : a system introduced in 2014 that favored websites protected with HTTPS. It has since become part of Google’s page interaction system.