Google how google works
Google how google works
How our business works
Ads help fund our products
Our mission to organize the world’s information and make it universally accessible and useful has always been core to everything we do at Google. It’s why we make so many of our products, like Search, Maps, and Gmail, accessible and free of charge to everyone.
Advertising is what makes it possible to offer our products to everyone. While we sell things like Pixel phones, apps on the Play Store, YouTube subscriptions, and tools for businesses, we make the vast majority of our money from advertising.
Second, businesses can buy ad space that we show on sites and apps that partner with us, like news publications and blogs. In this case, most of the money goes to the partner and helps fund their content. So ads not only help support Google but also many other websites and creators.
Ultimately, we earn most of our money by showing ads alongside relevant Search results on Google.com. If you’re interested, you can learn more about how we make money with advertising.
We don’t sell your personal information to anyone
We use your personal information to make our products more helpful to you. It’s how we can autocomplete your searches, get you home faster with Maps, or show you more useful ads based on your interests. But we never sell your personal information to anyone and you can use many of our products without signing in or saving any personal information at all.
Your data, your choice
When it comes to privacy, we know one size doesn’t fit all. That’s why we build powerful, easy-to-use privacy controls into your Google Account and directly into our products so you can choose the privacy settings that are right for you.
When we show you ads we give you transparency and controls so you can make informed decisions. If you’re curious why you’re seeing a given ad, you can select Why this ad for more information. If you no longer find a specific ad relevant, you can mute it. You can use Ad Settings to control the information about you that’s used to show ads. And if you don’t want to see personalized ads at all, you can turn them off at any time.
Because of advertising, we’re able to offer our products to users around the world free of charge, helping people find answers and get things done. But, when you use our products you trust us with your personal information. That’s why we never sell your personal information and why we give you powerful privacy controls. It’s a responsibility that comes with creating products that are accessible for everyone, everywhere.
How our business works
Ads help fund our products
Our mission to organize the world’s information and make it universally accessible and useful has always been core to everything we do at Google. It’s why we make so many of our products, like Search, Maps, and Gmail, accessible and free of charge to everyone.
Advertising is what makes it possible to offer our products to everyone. While we sell things like Pixel phones, apps on the Play Store, YouTube subscriptions, and tools for businesses, we make the vast majority of our money from advertising.
Second, businesses can buy ad space that we show on sites and apps that partner with us, like news publications and blogs. In this case, most of the money goes to the partner and helps fund their content. So ads not only help support Google but also many other websites and creators.
Ultimately, we earn most of our money by showing ads alongside relevant Search results on Google.com. If you’re interested, you can learn more about how we make money with advertising.
We don’t sell your personal information to anyone
We use your personal information to make our products more helpful to you. It’s how we can autocomplete your searches, get you home faster with Maps, or show you more useful ads based on your interests. But we never sell your personal information to anyone and you can use many of our products without signing in or saving any personal information at all.
Your data, your choice
When it comes to privacy, we know one size doesn’t fit all. That’s why we build powerful, easy-to-use privacy controls into your Google Account and directly into our products so you can choose the privacy settings that are right for you.
When we show you ads we give you transparency and controls so you can make informed decisions. If you’re curious why you’re seeing a given ad, you can select Why this ad for more information. If you no longer find a specific ad relevant, you can mute it. You can use Ad Settings to control the information about you that’s used to show ads. And if you don’t want to see personalized ads at all, you can turn them off at any time.
Because of advertising, we’re able to offer our products to users around the world free of charge, helping people find answers and get things done. But, when you use our products you trust us with your personal information. That’s why we never sell your personal information and why we give you powerful privacy controls. It’s a responsibility that comes with creating products that are accessible for everyone, everywhere.
How Google Works
Google Hiring Dos and Don’ts
How Google Works documents entertaining insider stories at Google from the perspectives of Eric Schmidt (ex-CEO of Google) and Jonathan Rosenberg (SVP of Products). Schmidt and Rosenberg were formidable forces that helped built Google from a three-year-old Silicon Valley startup in 2001, into a global internet giant today.
These are the ten commandments Google practices when it comes to hiring smart creatives, or “Googley Googlers”.
1. Hire people who are smarter and more knowledgeable than you are. Don’t hire people you can’t learn from or be challenged by.
To start the hiring process, Google forms a hiring committee. They follow the peer review practice of academia, instead of hierarchical corporate style. In universities, professors are hired through peer-based hiring with the intent to keep them in academia for as long as possible. That said, the hiring organization has to invest much more time and effort to get the salary package, incentives, benefits and job promotion done right.
Let’s say you are the interviewee.
Google hiring committee will research your background by reading your résumé and doing a Google search. They try to form a first impression of you before they meet you. Next comes the interview.
The interview gives them a chance to form a strong opinion of you. They want to learn who you are as a person — Are you a leader or a follower? Are you comfortable with the status quo, or are you eager to change?
Questions they may ask based on your résumé:
What was the low point in the project?
Why was the project successful?
Google has phased out mind-bending brainteasers so you may no longer see questions like this:
“If you have twelve coins, one of which is counterfeit and a different weight than the others, and a balance, how do you identify the counterfeit coin in just three weightings?”
(There is a right answer to the brainteaser above, though.)
Google wants to see candidates express their insights, ideas, and thought processes. Google wants to learn how you think. They realize the objective of an interview is to find the limits and boundaries of your capabilities. Rather than asking candidates to regurgitate their experiences and getting rehearsed responses, they ask about candidates’ experiences through an unexpected angle. Opinion questions are generally open-ended:
“How did you pay for college?”
“What books are you reading right now?”
“If I were to look at the web history section of your browser, what would I learn about you that isn’t on your résumé?”
When you enter the interview room, you will most likely get to see a maximum of five interviewers. There is a reason for this. Beyond five interviewers, every additional interviewer raises the cost, but only marginally improves the accuracy of hiring decision by less than 1 percent.
You can expect the interview session to be at most 30 minutes. If the hiring committee likes you a lot, you will get a second interview.
2. Hire people who will add value to the product and our culture. Don’t hire people who won’t contribute well to both.
Interviewees are evaluated based on four attributes criteria: (1) leadership, (2) role-related knowledge, (3) general cognitive ability, (4) Googleyness.
What is Googleyness?
Someone who is highly “Googley” thrives in ambiguity, solve problems creatively, takes action promptly and enjoys collaborating with people.
3. Hire people who will get things done. Don’t hire people who just think about problems.
Employees at Google create almost unattainable goals using a goal-setting system: Objectives and Key Results (OKRs). OKR is a system to define goals and track their outcomes. This gives Googlers a transparent measure of how their individual results match up with their overaching objectives.
Objectives are ambitious goals — “think 10X” — that trigger your growth in a slightly challenging manner. Key results are quantifiable, achievable, feasible in the immediate future, so you can start working on it today. Everyone grades his own OKRs on a scale of 0 to 1 by the end of a quarter or a year.
If you get a 1, the key results are too easy to achieve.
If you get a 0, it is too difficult and not worth doing.
If you get 0.6–0.7, that’s the best score one could aim for.
The fascinating part is that every employee updates and posts his own OKRs with scores made known publicly on the company-wide directory. Think of it as a social profile, or virtual achievement board of an employee. Anyone can search for another person at Google to learn what he is currently working on, and how he is actually progressing towards that goal.
4. Hire people who are enthusiastic, self-motivated, and passionate. Don’t hire people who just want a job.
Google Sky Map, a star map application for Android phones, was developed by a group of amateur astronomers, who happened to be Googlers. They developed it in the spare time they had at Google, called “20 percent time”.
20 percent time can be a Friday on a five-day work week. 20 percent time can be a 2-hour free time on a 10-hour work day. 20 percent time can also be 6 days in a 30-day month.
Google trusts that creativity and innovation, which are often haphazard leaps to success, cannot be forced by working harder. Thus Googlers are encouraged to devote 20 percent of their work time to work on something outside of their usual job description.
At some point, Gmail, Google News and Google Street View started as side project by Google employees during their “20 percent time”. Google’s move empowers employees with trust and dignity, autonomy and wider choices to pursue creative personal projects, before they scale up into a collaborative project.
It echoes with Cal Newport’s insight in So Good They Can’t Ignore You. People end up loving their career when they gain competence and autonomy from their jobs, while creating tangible impact on other lives.
Two years after Google Maps launched in 2005, Google sent cars to the streets to capture 360-degree panoramic photos of the street. However, the Street View team had a problem. There were narrow alleys, bicycle routes and pedestrian paths where cars were too big to drive through.
A Google engineer, Daniel Ratner built a tricycle to fix it. He pedalled to the streets a tricycle with a pole-mounted camera attached at the back, and photographed places in California such as LEGOLAND California.
As amusing as it looks (an Earth version of Mars rover, only with a rider), tricycle was the by far the most practical vehicle to travel the road less travelled. There are now different alternatives other than a tricycle: trekker backpack (for Grand Canyon), trolley (for White House), and snowmobile (for Alaska).
5. Hire people who inspire and work well with others. Don’t hire people who prefer to work alone.
On a Friday in 2002, Larry Page (Co-founder of Google) entered a query on the Google site. He searched for vintage motorcycles “Kawasaki H1B” on the Google search engine. Ads for helping immigrants get H-1B US visas popped up instead.
Maybe his search was too specific, he thought.
He typed in another query “french cave painting”. The search results were not even remotely close to his query. It came back with ads of online retailer who did not even sell paintings. AdWords search engine was giving users information which weren’t useful at all.
In any other company, this is what a CEO would do.
The CEO would choose the “best people” to resolve the issue.
The CEO calls upon the person-in-charge, head of ads team or even the best engineers. An emergency meeting would be arranged to discuss the problem, suggest and test a few solutions. The ads team would be demanded to solve the problem by a certain deadline. This top-down hierarchical process usually takes weeks or months, before the plan of action actually takes effect.
However, Page did something different.
Page printed out the search result pages with offending, irrelevant ads. He posted the printouts on a bulletin board in the kitchen, where anyone dropping by for a coffee could easily see. He wrote in all caps a callous remark beside the ads. Page’s comment could also be seen as a bold call-out.
Curiously, he did not call or email anyone from the AdWords team. He did not mentioned it to any of his colleagues or employees. He left work, then and there.
The next Monday morning, Page received an email reply from a group of five engineers. It was a bunch of problem analysis, suggested solutions, prototype implementation, and sample results of a core insight.
It was simply this insight — position of ads on the search page should be based on ads’ quality and relevancy to user’s keyword — that fundamentally changed the way Google search engine works today.
Ads could no longer get to the top of the search ranking by paying more advertising fees, or getting more user clicks. Ads have to be relevant to user’s search query. The higher the “ad relevance score”, the higher an ad would appear on the search page.
The problem was solved in a weekend.
The best part of it all? None of the five engineers (Jeff Dean, Georges Harik, Ben Gomes, Noam Shazeer and Olcan Sercinoglu) had direct responsibility for ads. None of them were even on the AdWords search team.
They simply saw Page’s post-it-note in the kitchen, and decided to fix the problem.
They solved the problem not because of accountability. They did it because of Google’s culture that applauds experimentation and embraces failures.
The best people were not chosen, they chose themselves. Taking a self-organized collective approach to problem-solving, is an epitome of swarm intelligence.
6. Hire people who will grow with your team and with the company. Don’t hire people with narrow skill sets or interests.
Carol Dweck’s book, Mindset dispels the infamous myth that one can only go so far because intelligence is inherited. This is how a fixed mindset would think.
If you have a fixed mindset, you would want to prove to others you are correct each and every single time. You would want to maintain that static self-image of constantly being correct.
It is normal to want to be correct and look smart all the time. But you won’t learn from your own mistakes. In a fixed mindset, failure is a painful, anxiety-inducing experience.
But it doesn’t have to be that way. A growth mindset is the way out.
Someone who learns from past failures, gets better at a rare skill over time, gains experience and grows more intelligent (and perhaps live happier). This is why a growth mindset could be better for living a life you want.
Dweck thinks that:
If you have a growth mindset, you’ll set “learning goals” — goals that will drive you to take risks without worrying so much about how, for example, a dumb question or a wrong answer will make you look.
Intelligence is the ability to adapt to change. 10 years is a short amount of time, if we assume a person can live to 80 years old. Facebook was founded in 2004. Twitter was founded in 2006. Google itself was founded in 1998. All three above are social media technology companies aged 10-20 years old as of today.
The world we are living now is changing at an incredibly fast rate, and the pace of change might be accelerating. (Moore’s Law says the processing powers of computers will double every two years.)
While Google seems to champion elitism, they prefer to hire people who are open to explore new ideas, learn things quickly and embrace change adeptly. Google realizes that a well-polished MBA-style business plan could sound great today, but rendered impractical the next year, month, week or even the next day. Even the best graduates from top business schools would need a healthy dose of intellectual humility to grow swiftly with the Google team.
You can have a plan, but know that it will change, probably a lot. The plan is fluid, the foundation stable. ― Eric Schmidt
In its search for exceptional talents, Google looks beyond the traditional metrics that are believed to predict career success: GPA, brand-name universities and expertise. (Same for some tech companies at Silicon Valley.) GPA and grades don’t matter as much as the four attributes that Google wants in a successful hire: leadership, knowledge, general cognitive ability, and Googleyness.
(See Rule #2. Hire people who will add value to the product and our culture.)
Instead of specializing for a highly specific role that exists today, do something that prepares you for the future tomorrow. Develop a growth mindset, acquire as many skills and abilities, get good at them as quickly.
7. Hire people who are well rounded, with unique interests and talents. Don’t hire people who only live to work.
The book talks about a personality test that you can perform to find out if someone you have newly met is a good work partner:
Imagine being stuck at an airport for six hours with a colleague; Eric Schmidt always chooses Los Angeles Airport (LAX) for maximum discomfort. Would you be able to pass the time in a good conversation with him?
If you could find someone who is able to pass the LAX test, that is great news. This might or might not be someone you enjoy being around 24 hours. This person could, however, offer you drastically different perspectives on a bunch of matters, challenges your viewpoints, prejudices and biases.
This could be a thought-provoking conversation partner with a decent amount of personality. If so, you have found an interesting, unique person whom you could learn, respect, admire, and work together.
8. Hire people who are ethical and who communicate openly. Don’t hire people who are political or manipulative.
Hire a good communicator who defaults to sharing openly, reliably, legitimately and authentically. Assume it is safe to tell the truth in all cases. In a debate, apply the Oprah Winfrey rule:
If you want to change people’s behavior, you need to touch their hearts, not just win the argument. ― Eric Schmidt
Everyone likes to hear that they are right most of the time, if not all the time. At the end of a debate or dilemma where you have to choose either side A or side B, simply say “you are both right”. Depending on the angle of perspective, there is generally a grain of truth in each viewpoint. This is paradoxical, but allowing people to voice reasonable objections is a valid approach to solving conflicts early on. If left unsolved, the conflict will still escalate, aggravate and resurface into more troubling matters. That could be a lot worse.
Communication is not about everyone agreeing to a certain outcome. It is a bunch of people with a range of opinions, rallying for the best outcome. It is about everyone being heard, and every opinion valued.
9. Hire only when you’ve found a great candidate. Don’t settle for anything less.
Compromise requires a certain side (or even both sides) to sacrifice its values, to lower its standards to less than desirable.
There could be a better approach to reach an agreement that does not need anyone to compromise or sacrifice. It takes creativity to think outside of the box, to reach a win-win situation that benefits and accommodates both sides.
Schmidt often drops nuggets of information about how he hired Sheryl Sandberg in the book. There was a rule of thumb (mentioned in the book, as of 2014) that half of Google employees had to be engineers, but Sandberg obviously was the outlier. She graduated with a bachelor’s degree in economics.
Schmidt offered Sandberg a rather ambiguous-sounding job. At that time, Sandberg had two offers. One was from Google, and another from an unnamed company with specified, well-defined job description. Yet Sandberg chose Google.
“When you’re offered a seat on a rocket ship you don’t ask, ‘What seat?’ You just get on,” Schmidt told her.
Sandberg built Google’s ads and sales team for six years, during which the ads and sales team expanded from 4 people to 4000 people. It was a job role that didn’t formally exist. She then became the chief operating officer (COO) of Facebook in 2008.
10. Hire people who believe in you and your idea enough to be willing to make the same sacrifices. Imagine the unimaginable. *
The most striking idea of this book on hiring is risk-taking. Hiring someone is just like taking a bet on someone, a bet on the future that this newcomer might bring forth. Big bets attract the best people, best resources, best investment, and best decisions, all of which attract even bigger opportunities. Paradoxically, big bets are easier to achieve than smaller bets, because the company cannot afford to fail.
Google likes to encourage its employees to think big, aim for moonshots and invent something new — “think 10X, not just 10% improvement”. Thinking big removes logical constraints, fosters creativity and gives employees the autonomy to pursue an innovative idea.
Suppose someone has this unworldly idea: put helium balloons up in the sky to transmit internet to the ground. Put these balloons high enough and keep them aloft for long enough, billions of people in rural places will get access to broadband Internet.
This idea, called Project Loon, may sound “loony” and silly, but it was brought to life by Google X:
Google X (research arm of Google company) has a simple Venn diagram that it uses to determine if it will pursue an idea.
Project Loon is at the intersection of Google X’s Venn diagram that overlaps three circles of innovation:
(1) It addresses a new big challenge on the sheer scale of people (billions of lives) and places affected (more than 30 million km).
(2) It offers a solution drastically different from anything that already exists in the market. To provide internet network, the existing way is to build a group of transmitting towers on the ground. Creating floating cell towers using balloons is conceptually radical, and radically useful.
(3) It has achieved surprising results with breakthrough technologies. Weather balloons typically rise and burst upon reaching 30 km above ground. Loon balloons are designed to overcome this issue. They are designed to withstand low temperature, low air pressure and UV radiation. They are designed to synchronize themselves with the wind, to avoid airplanes and weather events. Loon balloons can stay aloft at 20 km above ground for 100 days.
If an idea addresses a big opportunity (something new), offers a radical solution (something radically useful), and applies breakthrough technology (something surprising), then it is worth pursuing.
*The tenth commandment is originally not in Google’s Hiring Dos and Don’ts. It is somewhere in the book section “Believe Your Own Slogans”, and is added for completeness.
How Google Works
What began in the late 1990s as a research project helmed by Larry Page and Sergey Brin, two students in Stanford University’s Ph.D. program, is now one of the most influential companies in the world: Google. At first, the students’ goal was to make an efficient search engine that gave users relevant links in response to search requests.
While search is still Google’s core purpose, the company now provides services and goods ranging from (among many) email and photo storage to productivity software (the Google Docs suite), the internet browser Chrome, the mobile operating system Android, Chrome laptops and the Pixel mobile phone. Google has evolved from that two-man enterprise into a multibillion-dollar corporation. In 2015, it restructured and is now the jewel of parent company Alphabet, making it one of the biggest and richest companies in the world.
Google has long been the most visited site on the Web, too, making the company’s influence on commerce and culture undeniable [source: Lifewire]. Practically every webmaster wants his or her site listed high on Google’s search engine results pages (SERPs) because that almost always translates into more traffic. Google has also acquired other Internet companies, ranging from blogging services to YouTube. For a while, the company’s search technology even powered rival companies’ search engines: Yahoo relied on Google searches for nearly four years until developing its own search engine technologies in 2004 [source: Google].
In this article, we’ll learn about the backbone of Google’s business, its search engine. We’ll also look at other services Google offers. Then we’ll take a quick peek at some of the tools, both software and hardware, that Google has developed over the years. We’ll also learn more about the equipment Google uses to keep its massive operation running. Finally, we’ll take a closer look at Google, the company.
Google’s name is a variation of the word «googol,» which is a mathematical term for a one followed by 100 zeros. Page and Brin felt the name helped illustrate Google’s monumental mission: Organizing billions of bytes of data found on the Web.
How Google and its algorithm work
Contents
How a search engine like Google finds content
In this video Matt Cutts from Google explains the basics of how Google works. We’re going to go into a bit more detail than this video does. But it’s a great primer to the content.
As mentioned in the video Google crawls the web using a bit of a code called a ‘spider’. This is a small program that follows links from one page to the next and each page it lands on is copied and passed on to the servers. The web (hence spider) is huge, and as such if Google were to keep a record of all the content it found it would be unmanageable. This is why Google only records the page code and will dump pages it doesn’t think are useful (duplicates, low value, etc).
Spiders work in a very specific way, hopping from link to link discovering new pages. This is why if your content is not linked to it won’t get indexed. When a new domain is encountered the spider will first look for this page:
Any messages you have for the spider, such as what content you want to be indexed or where to find your sitemap, can be left on this page. The spider should then follow these instructions. However, it doesn’t have to. Google’s spiders are generally well behaved through and will respect the commands left here.
You can find out more about how robots.txt works here, where we cover some of the more technical aspects of SEO.
The spider itself is a small, simple program. There are lots of open source versions which you can download and let loose on the web yourself for free. As vital as it is to Google, finding the content is not the clever bit. That comes next.
Indexing
When you have a large amount of content you need a way to shortcut to that content. Google can’t just have one big database containing all the pages, which they sort through every time a query is entered. It would be way too slow. Instead, they create an index which essentially shortcuts this process. Search engines use technology such as Hadoop to manage and query large amounts of data very quickly. Searching the index is far quicker than searching the entire database each time.
Common words such as ‘and’, ‘the’, ‘if’ are not stored. These are known as stop words. They don’t generally add to the search engine’s interpretation of the content (although there are exceptions: “To be or not to be” is made up of stop words) so they are removed to save space. It might be a very small amount of space per page, but when dealing with billions of pages it becomes an important consideration. This kind of thinking is worth bearing in mind when trying to understand Google and the decisions it makes. A small per page change can be very different at scale.
Ranking algorithms
Google decides which query goes where through the algorithm. An algorithm is a generic term which means a process or rule-set that’s followed in order to solve a problem. In reference to Google, this is the set of weighted metrics which determines the order in which they rank the page.
Understanding the Google algorithm
The Google algorithm is not the mystery it once was and the individual factors and metrics which it is made up of are fairly well documented. We know what all the major on-page and off-page metrics are. The tricky bit is in understanding the weighting or correlation between them.
If you searched for ‘chocolate cake recipes’ the algorithm will then weight the pages against that search term.
Let’s take a simplified look at two metrics and how they might influence each other.
Metric 1 is the URL. The keywords might appear in the URL, such as: www.recipes.com/chocolate-cake
Google can see the keywords ‘chocolate cake’ and ‘recipes’ in the URL so it can apply a weighting accordingly.
Now on to Metric 2, the backlinks for the page. Lots of these might have the keywords ‘chocolate cake’ and ‘recipes’ in them. However Google would then down-weight this metric because if the keywords appear in the URL you would expect them to appear in the backlinks, relevant or not. Conversely, Google might choose to apply more weight to Metric 2 if the keywords didn’t appear anywhere in the URL.
All the different factors Google looks at affect each other. Each one may be worth more or less (in the weighting) and the relationship between them is constantly shifting. Google issues hundreds of updates every year, constantly tweaking this. It is most commonly this relationship and weighting that’s changed more than the metrics themselves. When this does happen it is usually in a more major update, such as Penguin or Panda.
The different metrics can be broken down into four key sections:
Relevance
How relevant is the content to the query? The indexer is the first test on this, determining if it should appear in the results at all. However, this is taken a step further in order to rank the keywords. It makes sense that when searching for something, you want to see the most relevant results possible.
Relevance is determined by a mix of on-page and off-page factors. Both of these focus on the placement of keywords, such as in page titles and anchor text. Some metrics are a combination of these. For example, if the domain as a whole is seen to be relevant to the search term, this is going to boost the relevancy score of the individual page being scored. If you want to find out more about this I recommend reading my article ‘How search engines use keywords’.
Authority
Authority has its roots in PageRank, invented by Larry Page (hence the name). It’s the backbone of how Google ranks content. Understanding PageRank is part of the key to understanding how Google works, but it’s worth remembering that there are hundreds of additional factors which can also affect ranking, and PageRank is less important than it was in the past.
PageRank is often explained in terms of votes. Each link to a page is a vote, the more votes it has the better it should rank. If a page with a lot of votes links to another page, then some of that voting power is also passed on. So even if a page only has one link, if that link is from a page which has a lot of votes, it may still rank well and pages it links to will also benefit from that. The value passed from page to page via links is known as link juice or page juice.
Relevance is also important in the context of authority. A link with relevant anchor text may pass on more weight than a link which is not from a relevant site and does not have relevant anchor text, and which Google is more likely to disregard in the context of that search result.
Trust
This is an anti-spam algorithm, focused on making it harder to artificially manipulate the search results. Google has a love-hate relationship with SEO and the trust mechanism is part of it. On the one hand, lots of SEO is about creating great content and user experience. On the other, it’s also about trying to artificially manipulate what Google has determined as the natural order of the results.
Trust metrics are very hard to manipulate and they give Google greater confidence in the other metrics. Things like the age of the content, or the domain are trust metrics. If you have lots of links from ‘bad neighbourhoods’ (think red light district) these links are not only going to be worthless but will also make Google think twice about ranking your site for that ‘chocolate cake recipe’ search. In the same way if the page or domain links out to bad neighbourhoods it’s going to damage those trust metrics.
Google is actually a domain registrar, meaning they can see all the whois data for different domains. This allows them to incorporate information, such as how often a domain has changed hands or how long until the registration expires, into those trust metrics. These are much more difficult to manipulate.
Usability
Google wants the content it displays in its search results to be attractive to humans as well as search engine robots. There is a set of metrics which is dedicated just to these factors. Having great content but then, for instance, covering it in ads is not going to make for a great user experience. This is why Google will down-weight a page where the ad placement is overly prominent.
Page speed is another important factor; pages that load too slowly are an annoyance to searchers, causing people to click back to the search results and pick another page. Google wants people to keep using Google and so it’s in their interest that the results they show load quickly. They measure page speed from the HTML but may also use Chrome user data.
Results type and personalisation
If you’re searching on a mobile phone that’s going to display a different set of results than if you are searching on a desktop computer. The actual results returned from the indexer (so at a low level) will be different. It’s not just device type which affects the results you see though, Google may choose to show results in an entirely different format depending on the search terms you use.
Localised searches are weighted differently and show in a different results page format to, for instance, product searches. You also have mixed media searches where Google may return results including videos and images. Some searches have dedicated results pages for a very narrow set of terms. These are commonly related to current events such as sports games or elections.
Another factor is personalisation. What you have previously searched for will influence the results that Google returns. There is a degree of machine learning at play here. So where someone searches for one type of result consistently Google will assume that future similar searches will be of the same nature. This is especially prominent for ambiguous searches, where one word has multiple meanings.