What is the difference between Panda and Penguin?

Update: Over the last five years, Google has modified both algorithms to continue to ensure quality websites that aren’t gaming the system rank. We expect that Google will continue to refine both algorithms to improve the search results.
A lot of people ask us to do SEO evaluations, usually looking for how Panda or Penguin ate their site, or better put, pushed their site down in the search ranking. So it makes sense to explain the difference between Panda and Penguin and why you may or may not be a victim of one or the other or in a lot of site we look at…neither.
There’s a lot to Google’s Panda and Penguin algorithms
Before we get into Google Penguin and Panda, it’s helpful to understand that each is a part of Google’s search algorithm. The algorithm is a mathematical formula involving up to 200 variables; which determines the rank of each website in a Google search. The algorithm takes into account many factors that some SEO have no control over, such as the user’s past history. One thing people should realize about the algorithm is that its super secret. Google will tell you bits and pieces but will not give you the formula. Its as secret as the formula locked in a vault in Atlanta.
Understanding the Penguin algorithm
Google Penguin is the latest update to Google’s algorithm. This update is aimed at websites that are using tactics that are considered a way to game Google’s searches. When Google indexes a site, it looks at places for specific keywords. Some firms have used this fact and stuffed keywords onto a site, or hidden text from the user, but make it visible to Google, or they get lots of links from illegitimate websites that Google now consider to be spam. To date, we have not reviewed a site that has been hit by Penguin. Most of the sites we review end up suffering from a lack of updating or issues relating to Google Panda.
How does Google Panda effect rankings?
Google Panda is the change to the algorithm we see that effects a lot of people who have old sites. To understand Google Panda, it helps to understand Google’s core mission. Google wants to deliver the best results for what you are searching. They do NOT want to deliver websites they consider to be low quality and this means when people go to a site from Google’s search, if you go back from that search, Google notices it and pushes you down in the search rankings. Some of the factors we have seen effect sites, are poor site design, sites that don’t reference their articles through links, sites that are slow to load, sites that use duplicate content over and over again. The bottom line is you need to have a well designed site and creates original content.
However, while Panda and Penguin have gotten most of the news and therefore excuses from site owners, there are other errors we see day in and day out that have nothing to do with either update. One of the most common is not updating your site frequently, and expecting to be ranked number one without any effort. Another is using the same keywords. For example, using your company name over and over again. Or, our favorite: having blank spots where keywords are supposed to go. How is Google going to index you without any keywords?
So, in conclusion, Panda is about getting Google to deliver the best quality websites to your search results. Penguin keeps people from gaming the system.