Mill CPU Architecture

The Mill CPU architecture is a novel belt machine-based architecture for general purpose computing, which has been under development by Ivan Godard and his startup Mill Computing, Inc. (East Palo Alto, California; formerly Out Of The Box Computing) for ten years. Mill Computing claims it has a "10x single-thread power/performance gain over conventional out-of-order superscalar architectures" but "runs the same programs, without rewrite".

It uses novel temporal register addressing scheme "The Belt", which has been proposed by Ivan Godard, to greatly reduce the complexity of CPU hardware (specifically the number of internal registers). While somewhat harder to read and debug than general-purpose register names, it is recommended that it be perceived as a moving "conveyor belt" where the oldest values "drop off" the belt into oblivion. The elimination or registers allows not to implement complex register renaming schemes.

Mill uses a VLIW-style encoding to store up to 33 simple operations in wide instruction word. Mill uses two program counters, and every wide instruction is split into two parts. One of program counters counts backwards. In result, the code of every linear instruction block is executed from its middle to outside by two almost independent decoders.

There are several versions of the Mill CPU in development: Tin (low-end) and Gold (targeted to high-performance market). Company estimates that dual-core Gold chip implemented with 28 nm may work at 1.2 GHz with 28 typical TDP and performance of 79 billion operations per second.

The OOTBC (Mill computing) was criticized by Linley Gwennap in 2013 for absence of working compiler and lack of estimations in conventional benchmarks.