If you’re new to the world of SEO or search engine optimization, and/or web development, you’ve probably repeatedly come across the advice to ensure an internet property is mobile-friendly. Obviously, this is due to the fact that many consumers browse via handheld devices. 

But, websites are still built on desktop machines. And, there are optimization techniques that are almost entirely unique to desktops. This means search engines must index both types of sites - mobile and desktop to deliver the right interface when requested. 

Google maintains separate search indexes for desktop and mobile devices to ensure that users receive the most relevant and optimized search results based on their device preferences and browsing habits. Here's why Google maintains these two separate indexes:

• User experience optimization. Mobile users often have different preferences and behaviors compared to desktop users. For example, mobile users may prioritize quick access to information, location-based results, or mobile-friendly websites. By maintaining separate indexes, Google can tailor search results to meet the unique needs and expectations of mobile users, optimizing the user experience and increasing user satisfaction.

• Mobile-first indexing. With the widespread adoption of mobile devices for internet browsing, Google introduced mobile-first indexing, which prioritizes the mobile version of a website's content for indexing and ranking. By maintaining a separate mobile index, Google can effectively crawl, index, and rank mobile-friendly content, ensuring that mobile users receive the most relevant and up-to-date search results.

• Algorithmic differences. Google's ranking algorithms may take into account different factors when evaluating desktop and mobile search results. For example, mobile search results may prioritize factors such as page loading speed, mobile-friendliness, and location relevance, whereas desktop search results may focus on factors like content depth, multimedia integration, and desktop optimization. By maintaining separate indexes, Google can apply algorithmic adjustments and optimizations tailored to each device type.

• Accelerated Mobile Pages (AMP). Google's Accelerated Mobile Pages (AMP) project aims to deliver faster and more responsive web experiences for mobile users. AMP pages are indexed separately in Google's mobile index and may receive preferential treatment in mobile search results, especially in situations where speed and performance are critical factors for user satisfaction.

• Enhanced search experience. By maintaining separate indexes for desktop and mobile devices, Google can provide users with a more tailored and optimized search experience. This includes delivering mobile-specific features such as click-to-call buttons, app deep links, and mobile-friendly snippets, as well as prioritizing mobile-optimized content and websites in mobile search results.

Overall, Google maintains separate search indexes for desktop and mobile devices to ensure that users receive the most relevant, timely, and optimized search results based on their device preferences and browsing behavior. 

By tailoring search results to the specific needs of desktop and mobile users, Google aims to enhance the overall search experience and provide users with the information they're looking for, regardless of the device they're using.