Design

SETI@home's data is recorded at 5 Mbps at the Arecibo Observatory in Puerto Rico. SETI@home used 35 GB digital linear tapes. The recording time per tape is 16 hours.

With one-bit complex sampling this yields a frequency band of 2.5 MHz which is enough to handle doppler shifts for relative velocities of up to 260 km/sec (or about the rate of the Milky Ways galactic rotation).

The frequency-band is like many other SETI-projects centered at the Hydrogen-line (1.42 GHz) because man-made transmissions are forbidden here by an international treaty.

SETI@home's computational model is simple. The signal data is divided into fixed-size work units distributed via the Internet to the clients. The client program computes a result (a set of candidate signals) and returns it to the server. As mentioned in the introduction there is no communication between clients.

SETI@home employs redundant computation. Each work unit is processed multiple times to compensate the detection and discard of results of faulty processors or malicious users. A redundancy level of 2 or 3 is adequate for this.

The generation of work units happens at a bounded rate. Also clients asking for work are never turned away. This increases the redundancy level the more users the project has and the higher the average speed per user gets. As the quantities increased greatly over time the clients have been revised to do more computation per work unit in order to keep the level of redundancy at the intended level. The server complex creates and distributes the work units to minimizes tape handling.

--Ertelt 14:49, 31 Oct 2005 (CET)