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SETI@home ("SETI at home") is a grid computing (distributed computing in the project's own terminology) project using Internet-connected computers, hosted by the Space Sciences Laboratory, at the University of California, Berkeley, in the United States. SETI is an acronym for the Search for Extra-Terrestrial Intelligence.

The Purpose of SETI@Home

The 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 participants worldwide, the project is the grid computing project with the most participants to date.

Anybody can participate by running a free of charge program that downloads and analyzes radio telescope data.

It performs four tests:

  • searching for spikes in power spectra,
  • searching for Gaussian rises and falls in transmission power, possibly representing the telescope beam's main lobe passing over a radio source,
  • searching for triplets, three power spikes in a row,
  • searching for pulses possibly representing a narrowband digital-style transmission.

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.


Since 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 1021 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. There, it is divided, in both time and frequency domains[1][2], to form the 0.25 Mbyte chunks (called work units) 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. The work units overlap in time, but not in frequency[3].

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 discrete Fourier transforms at various chirp rates and durations.

The project also searches for pulsing 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 is 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.


File:SETI v4 18.png
SETI@home version 4.18
SETI@home under classic client (version 3.08)

The 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 grid computing application.

SETI@home, in addition to its altruistic use to aid SETI, is quite useful as a stress testing tool for computer workstations. SETI@home is often used to check on the reliability of a computer configuration when overclocking.

SETI@home has completed most of the process of transferring its computing software to a new software platform called Berkeley Open Infrastructure for Network Computing (BOINC). The project now calls the original software platform SETI Classic.

BOINC will allow testing for more types of signals as well as let users contribute to other grid computing projects running on the BOINC platform.

There are minimum requirements for a computer 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, Linux and BeOS.

The results of the data processing can be sent automatically, next time the participant is on the internet, or the software can be set to ask permission before logging on to the internet.

Project futures

There are future plans to get data from the Parkes Observatory in Australia to analyse the southern hemisphere.

Competitive aspect and SETI@home farms

SETI@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' [4] in the US led the statistics for many years but has recently been overtaken by both SETI.Germany and OcUK (Overclockers UK). One of the largest teams formed was Team Art Bell (named after the American talk radio host) with over 13,000 members.

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 98 SE "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.

Some SETI@home users are such fanatics that they have even mis-utilized company resources to gain work-unit results – with at least one individual getting fired for running SETI@home on a enterprise production system, e.g. as reported by Associated Press on October 8, 2004.[5]

Threats to the project

Like any project of indefinite duration, there are factors that may result in its eventual termination. Some of these are detailed below:

Participants not prepared for the long term

Even before the project went live, people were commenting, on SETI related public mailing lists, that many people might have false expectations of the likelihood of any one project finding an extraterrestial intelligence, or of one being found within a specific amount of time. Their fear would be that this would be bad public relations for SETI as a whole. Although it is not clear how many people have become disillusioned as a result of unreasonable expectations, there have certainly been vociferous cases.

Also, many participants are participating for reasons other than the science and will be affected by changes in fashion.

Alternative distributed computing projects

When the project was launched there were few alternative ways of donating computer time to research projects, but now there are a lot more options, and therefore SETI@Home has to compete in a market. Different people have different value systems and so, for example, some prefer projects with a realtively high chance of benefitting humanity in the short term; others avoid these because they are more likely to be associated with commercial profit.

There is also competition for screensavers and competition vehicles.

More restrictive computer use policies in businesses

As of 2005-10-16, approximately one third of the processing [6] for the non-BOINC version of the software was performed on work or school based machines. Whilst much of this has been done by network administrators themselves, over the duration of the project, who have generally reduced the rights of ordinary users to configure their own machines. A number of adminstrators have also expressed concerns about the automatic software updating in BOINC.

To some extent, this may be offset by better connectivity to home machines.


Currently there is no government funding for SETI research and private funding is always limited. Berkeley Space Science Lab have found ways of working with small budgets, and the project has received donations allowing it to go well beyond its original planned duration, but it still has to compete for limited funds with other SETI projects and other space sciences projects.

Unofficial Clients

A number of individuals and companies[7] made unofficial changes to the distributed part of the software to try and produce faster results, but this compromised the integrity of all the results. As a result, the software had to be updated to make it easier to detect such changes.

BOINC allows unofficial clients and relies more on cross-checking[8].


See also

External links

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