Many metrics, including size, color, and so forth, so you can make adjustments to maximize the value of the placements.
AdSense for Search
This is another program whereby Google allows you to add a Google Search box to your website. By doing this, visitors to your site can search the entire internet from your website itself. In a way, your site becomes a host to Google. Except you make money!
The search results page that is displayed when a visitor on your website searches through the search box on the site itself, also displays Google Ads (AdWords ads) next to the usual listings, just as it would on Google.com. If the visitor clicks on any of these Google Ads, you get paid as well. Thus, with AdSense for Search you can enhance your income potential beyond what just the content of your actual site can provide.
AdSense for Search offers all the same options and controls as AdSense for Content. These include ad customization, ad filtering, monitoring and tracking results, and so on.
Google AdSense Premium service
The AdSense Premium service provides advanced functionality and features, provided your website qualifies for it - which in fact very few sites do.
As a base requirement, your website should receive at least 5 million search queries or 20 million page views a month to qualify for the Premium service. (We're betting if your sites qualify for this level of service, you already know all about AdSense!)