Nehalem is the codename for an Intel processor microarchitecture released in November 2008. Nehalem was used in the first generation of the Intel Core processors (Core i7 and i5, with Core i3 being based on the subsequent Westmere and Sandy Bridge designs). Nehalem is the successor to the older Core microarchitecture (Intel Core 2 processors). The Intel codename "Nehalem" was taken from the Nehalem River. It is an architecture that differs radically from Netburst, while retaining some of the latter's minor features. Nehalem-based microprocessors use the 45 nm process, run at higher clock speeds, and are more energy-efficient than Penryn microprocessors. Hyper-threading is reintroduced, along with a reduction in L2 cache size, as well as an enlarged L3 cache that is shared among all cores. Nehalem was replaced with the Sandy Bridge microarchitecture, released in January 2011.