The Pentium's Mysterious ×3 Circuit: A Deep Dive into Chip Design
In 1993, Intel released the high-performance Pentium processor. This article delves into the surprisingly complex design of a seemingly simple circuit within the Pentium: the multiply-by-three circuit (×3 circuit). This circuit is part of the floating-point multiplier; the Pentium uses radix-8 multiplication, which is faster than binary multiplication, but multiplication by three requires special handling. The article explains how this circuit combines techniques like carry lookahead, Kogge-Stone adders, and carry-select adders to maximize performance. Analysis of microscope images of the chip reveals the intricate structure of the ×3 circuit and its crucial role in the Pentium, highlighting the ingenuity and technical innovation in processor design.