SETI@homeSETI@home ("SETI at home"
) is a distributed computing project for Internet-connected home computers, hosted by the University of California, Berkeley, in the United States.
SETI is an acronym for the Search for Extra-Terrestrial Intelligence.
SETI@home under classic client (version 3.08)
SETI@home version 4.18The purpose of SETI@home is to analyze data incoming from the Arecibo radio telescope, searching for possible evidence of radio transmissions from extraterrestrial intelligence. With over five million users worldwide, the project is the most successful example of distributed computing to date. Anybody can participate by running a free program that downloads and analyzes radio telescope data.
It performs three main tests:
- searching for Gaussian rises and falls in transmission power, possibly representing the antenna passing over a radio source
- searching for pulses possibly representing a narrowband digital-style transmission
- searching for triplets, three pulses in a row
While the project has not found any conclusive signs of extraterrestrial intelligence, it has identified several candidate spots for further analysis. On September 1, 2004, an interesting signal SHGb02+14a was announced.
FiguresSince its launch on May 17, 1999, the project has logged over two million years of aggregate computing time. On September 26, 2001, SETI@home had performed a total of 10^21 floating point operations. It is acknowledged by the
Guinness Book of World Records as the largest computation in history. With about 500,000 in the system, SETI@home has, by conservative estimates, the ability to compute 100 TeraFLOPS.
How does the system work?Data is recorded on high density tapes at the Arecibo Observatory in Puerto Rico, about one 35 Gbyte tape per day, then mailed to Berkeley. It is then divided into 0.25 Mbyte chunks which get sent from the SETI@home server over the internet to people around the world to analyze. Arecibo does not have a high bandwidth internet connection, so data must go by postal mail to Berkeley at first.
SETI@home searches for strong narrow band signals. The process is somewhat like tuning a radio set to various channels, and looking at the signal strength meter. If the strength meter goes up, that gets the attention. More technically, it involves a lot of digital signal processing, mostly Fourier transforms at various chirp rates and durations.
The project also searches for pulsing and drifting signals, and signals which match the antenna beam pattern as the telescope slews across the sky. The analysis software can search for signals with about one-tenth the strength of those sought in previous surveys, because it makes use of a computationally intensive algorithm called
coherent integration that no one else has had the computing power to implement.
Data are merged in a database using SETI@home computers in Berkeley. Interference is rejected, and various pattern-detection algorithms are applied to search for the most interesting signals.
SoftwareThe SETI@home distributed computing software, available for all major operating systems, runs either as a screensaver or continuously while a user works, making use of otherwise wasted processor power for research. SETI@home was the first popular distributed computing application. After six years of fruitless searching, however, some critics now believe that unused computer cycles could be better spent on projects that have more direct benefits to the human race, such as Folding@home.
SETI@home, in addition to its altruistic use to aid SETI, is quite useful as a stress testing tool for computer workstations. Since it uses error-correction algorithms to verify the results of the computations, SETI@home is often used to check on the reliability of a computer configuration when overclocking.
There are future plans to get data from the Parkes Observatory in Australia to analyse the southern hemisphere. SETI@home is in the process of transferring to a new software platform called Berkeley Open Infrastructure for Network Computing (BOINC) that will allow testing for more types of signals as well as let users to contribute to other distributed computing projects running on the BOINC platform.
There are minor technical requirements in order to participate in the project. Systems running Windows OS need at least 32 MB of RAM, the ability to display 8-bit graphics in 800x600 resolution, 10 MB of disk space, and an Internet connection. For Macintosh, a PowerPC processor and Mac OS 7.5.5 or later is required. SETI@home software is also supported by UNIX and Linux.
The results of the data processing can be sent automatically, next time the users are on the internet, or it can be set to ask permission before logging on to the internet.
Competitive aspect and SETI@home farmsSETI@home users quickly started to compete with one another in an effort to process the maximium number of work units. Teams were formed to combine the efforts of individual users. The Ars Technica 'Team Lamb Chop' (see
link) in the US led the statistics for many years but has recently been overtaken by both SETI.Germany and OcUK – OverClockers UK.
Some users were able to run the application on PCs they had access to at work (an act known as Borging, after the assimilation-driven Borg of
Star Trek: The Next Generation. Others simply collected large quantities of equipment together at home and created "SETI farms" (typically consisting of motherboard, CPU, RAM and PSU only) arranged on shelves as diskless workstations running either LINUX or Windows 98se "headless" (without a video card).
As with any competition, numerous attempts have been made to 'cheat' the system and claim credit for work that has not been performed. To combat cheats, the organisers send out each work unit multiple times and only stop sending out the same work unit when they receive back results from two or more different users that exactly agree.
