Application Processors
An Application Processor (AP) is the main processing unit of a system, commonly designed as a System on Chip (SoC). APs are sometimes also considered microprocessors, as opposed to microcontrollers. Another regularly used term is Central Processing Unit (CPU). While design approaches and names have changed over the years, psi-spec is concerned with the kind of processors that feature a Memory Management Unit (MMU) and DRAM, allowing for many concurrent tasks and processing large amounts of data.
System on Chip
An SoC integrates application processing units with peripherals via internal system buses, all packaged into one chip. Common buses are defined by the AMBA standards and the WISHBONE Interconnect Architecture. Some vendors have their own designs, such as AMD's Infinity Fabric. A bus is generally a set of physical interfaces and corresponding protocols. Parts of an SoC are called blocks.
