Intel iAPX 432

Lore & Background

Design began in 1975 as the 8800, a clean-sheet design that did not follow previous machine code conventions. The project was managed by Bill Lattin, with Justin Rattner as lead engineer (though one source states Fred Pollack was lead engineer). The team moved from Santa Clara to Portland in March 1977. The architecture was a stack machine with no visible general-purpose registers, supporting object-oriented programming, garbage collection, multitasking, and memory management directly in hardware and microcode. It was intended to be programmed entirely in high-level languages, with Ada as the primary language; Intel iMAX 432 was an operating system written entirely in Ada.

The first implementation was too advanced for the semiconductor fabrication techniques of the era and had to be implemented on two separate integrated circuits: the 43201 (instruction fetch and decode) and the 43202 (execution). Most systems also included the 43203 Interface Processor for I/O and an Attached Processor (an Intel 8086). In 1983, Intel released the 43204 Bus Interface Unit and 43205 Memory Control Unit for multiprocessor systems with up to 63 nodes. The design's complexity limited clock speed; actual devices were specified for maximum clock speeds of 4 MHz to 8 MHz.

The iAPX 432 was referred to as a 'micromainframe'. Its instruction set used bit-aligned variable-length instructions. The two-chip implementation limited speed, and the capability architecture needed large associative caches that the chips had no room for. The 432 performed typical benchmarks at roughly 1/4 the speed of the Intel 80286 at the same clock frequency in early 1982. This performance gap, combined with high prices, led to little use and eventual discontinuation.

Reader's Guide

The iAPX 432 is significant as Intel's first 32-bit processor and an ambitious attempt to create a high-level language computer architecture with hardware support for object-oriented programming, garbage collection, and multitasking. Its failure stemmed from being too advanced for the semiconductor fabrication techniques of its era, requiring a two-chip implementation that was expensive and slow. The performance gap—roughly one-quarter the speed of the contemporary 80286—combined with high prices, prevented market adoption. The loss of sales from existing designs due to the compatible Zilog Z80 led Intel to introduce the 8086 as a stop-gap solution in 1977 while the 432 matured; the 8086 went on to form the basis of Intel processors to this day. Although some early 8086, 80186, and 80286 systems used the iAPX prefix for marketing, the iAPX 432 and 8086 lines are completely separate designs with different instruction sets. The 432's capability architecture came to be regarded more as an implementation overhead than as simplifying support. It was discontinued in 1986.

Did You Know?

• The iAPX 432 was Intel's first 32-bit processor design, introduced in 1981.
• It was implemented on two separate integrated circuits: the 43201 and 43202.
• Intel iMAX 432, an operating system for the 432, was written entirely in Ada.