SETI is a search for positive evidence of intelligent life originating or existing some place other than earth. To find this evidence they search the radio waves in certain frequencies for signals and patterns that could prove there existence. A radio signal consists of two parts, a carrier wave which is the main frequency per se 4.1ghz or 105mhz. Planted on or in the carrier frequency is the information, either by AM (mplitude modulation) which is just a fancy way of saying increasing and decreasing the voltage to make the carrier stronger or weaker in a regulated fashion and very small incremnets. The other way is via frequency modulation (FM) whcih varies the frequency in small increments to get the information accross.
A work unit is a standard size packet of information that needs to be anylyzed for the evidence above. By using a standard size packet I assume it makes it easier to run "distributed computing" and keep track of the information out there.
The seti program when in the low priority setting only runs when nothing else is active, seti is cpu intensive and runs the cpu at 100% of the possible cpu processing.
How they figure out what is a good signal and what isn't is way above me. Hope this helps and you decide to join our team.
Everything my friends so far have explained is correct, but one very important area that was only briefly brushed against is the fact that the SETI at Home project was the very first experiment and still a cutting edge example of the principle of "Distributed Computing". That is to say that in order for Berkeley to have analyzed the amount of data that has went through the project since it's start by ordinary methods would have required fulltime access to mutiple SUPER COMPUTERS at an unbelievable cost. Instead Berkeley developed a way of dicing the data up into small workable packets called "Work Units", which it then distributes to normal PCs via the internet. These PCs run a client program in the background taking advantage of all those unused processor cycles which every PC has an abundence of to analyze the data, which when a WU is completed is then returned to Berkeley who compiles the results from all those participating from around the world and reviews these results for interesting discoveries.
While SETI does stand for Search for Extra Terrestrial Intellegence, the results of analyzing all this radio data has yielded valuable information about other things connected with Astronomy and to some degree Physics as it relates to Black Holes, Dark Matter, and other physical features of our universe.
Some famous individual once stated, "one can not know where one is or where one is going, until one understands where one has been". As we analyze this data coming to us from great distances we are in fact "looking back into time", and hopefully are learning from where we began in order to better understand where we are headed.