non-homogeneous register architecture
Non-homogeneous register architectures are frequently encountered in Application Specific Instruction Set Processors (ASIPs). These processors usually have a set of very specialized functional units, and associated registers, that are used to efficiently implement operations with performance requirements that frequently occur in the application domain of the processor. Examples of these type of units include Multiply and Accumulate Units (MAC) and Address Calculation Units (ACU). [Source: Optimal Code Generation for Embedded Memory Non-Homogeneous Register Architectures]
Contrast with homogeneous register architecture.