The SPS straddles the Swiss-French border at the CERN site in Geneva. The Super Proton Synchrotron (SPS) was originally going to built along with a new CERN centre in Europe, separate from the Geneva research centre, but a series of political arguments resulted in the decision that it be built alongside the existing Synchro-Cyclotron and Proton Synchrotron accelerators at the Geneva site, in the 1970s.
The SPS is a circular accelerator, 6 km in circumference, buried underground. It was originally built to accelerate protons but has also operated as a proton-antiproton collider, a heavy-ion accelerator, and an electron/positron injector for the newer Large Electron Positron (LEP) collider.
As a proton-antiproton collider in the 1980s, it provided CERN with one of its greatest moments - the first observations of the W and Z particles, the carriers of the weak force.
The SPS can also accelerate lead ions to an energy of 170 GeV per nucleon, with 208 nucleons in the lead nucleus. In 1998, this was the highest energy obtained in the world, and it serves the study of the quark-gluon plasma which may have occured shortly after the big bang.
Each winter, the SPS is shut down for routine maintenance (in 2000, for instance, shutdown is scheduled for the 2nd of November). In addition to the annual shutdown, a fire on Tuesday May 13th in 1997 caused an additional 80 days worth of delays, as can be seen on the throughput graph shown to the left.