Since the first Intel microprocessor, technology has significantly evolved and so has the complexity of the processor architecture. The initial set of instructions, although it was and still is quite powerful, is not enough for some tasks (and here we have to admit that the number of such tasks is growing as time goes by). The solution adopted by Intel is nice and quite user friendly: Instruction Set Architecture Extensions (ISA Extensions). Intel has gone a long way from MMX (unofficially, MultiMedia eXtension) to SSE4.2, AVX, and AVX2 extensions, which introduced support for 256-bit data processing and AVX-512, which allows the processing of 512-bit data and extends the number of usable SIMD registers to 32. All of these are SIMD extensions, where SIMD stands for single instruction multiple data. In this section, we will particularly pay attention to the AES-NI extension and partially to SSE (which will be covered in more detail in Chapter 5, Parallel Data Processing).