As CPU design evolved into using faster local buses and slower peripheral buses, Intel adopted the "dual independent bus" (DIB) terminology, using the external front-side bus to the main system memory, and the internal back-side bus between one or more CPUs and the CPU caches. This was introduced in the Pentium Pro and Pentium II products in the mid to late 1990s. The primary bus for communicating data between the CPU and main memory and input and output devices is called the front-side bus, and the back-side bus accesses the level 2 cache.