Although the initial implementations use single four-quadrant links, the QPI specification permits other implementations. Each quadrant can be used independently. On high-reliability servers, a QPI link can operate in a degraded mode. If one or more of the 20+1 signals fails, the interface will operate using 10+1 or even 5+1 remaining signals, even reassigning the clock to a data signal if the clock fails. The initial Nehalem implementation used a full four-quadrant interface to achieve 25.6 GB/s, which provides exactly double the theoretical bandwidth of Intel's 1600 MHz FSB used in the X48 chipset.