Rivina is an experimental 64-bit PowerPC microprocessor built by IBM in 2000. It was the successor to "guTS" (Gigahertz Unit Test Site) and the purpose of both was to build a processor able to reach very high frequencies. They were the first microprocessors to reach and surpass the 1 GHz mark.
Project work was conducted by fewer than twenty engineers over a course of two years. The idea was to use aggressive circuit design techniques, a carefully crafted floorplan and microarchitecture while keeping a short six stage pipeline. While guTS only supported a subset of about 100, mainly integer instructions, of the PowerPC instruction set, Rivina used the complete 64-bit PowerPC specification including dual precision floating point and address translation. guTS had a small single cycle 4 kB L1 cache, and Rivina used a two-cycle, two set associative 64 kB cache instead.