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Rapid Execution Engine:
Two Arithmetic Logic Units (ALUs) on the Pentium 4 processor are clocked at twice the core processor
frequency. This allows basic integer instructions such as Add, Subtract, Logical AND, Logical OR, etc. to
execute in half a clock cycle. For example, the Rapid Execution Engine on a 1.50 GHz Pentium 4 processor
runs at 3 GHz.
256KB, Level 2 Advanced Transfer Cache:
The Level 2 Advanced Transfer Cache (ATC) is 256KB in size and delivers a much higher data throughput
channel between the Level 2 cache and the processor core. The Advanced Transfer Cache consists of a 256-
bit (32-byte) interface that transfers data on each core clock. As a result, the Pentium 4 processor 1.50 GHz
can deliver a data transfer rate of 48 GB/s. This compares to a transfer rate of 16 GB/s on the Pentium III
processor at 1 GHz. Features of the ATC include:
Non-Blocking, full speed, on-die Level 2 cache
8-way set associativity
256-bit data bus to the level 2 cache
Data clocked into and out of the cache every clock cycle
Advanced Dynamic Execution:
The Advanced Dynamic Execution engine is a very deep, out-of-order speculative execution engine that
keeps the execution units executing instructions. The Pentium 4 processor can also view 126 instructions
in flight and handle up to 48 loads and 24 stores in the pipeline. It also includes an enhanced branch
prediction algorithm that has the net effect of reducing the number of branch mis-predictions by about
33% over the P6 generation processor’s branch prediction capability. It does this by implementing a 4KB
branch target buffer that stores more detail on the history of past branches, as well as by implementing a
more advanced branch prediction algorithm.
