80386

80386. Introduced by Intel in October 1985, the 80386 was a landmark 32-bit microprocessor that fundamentally transformed the personal computer industry. It established the dominant x86 architecture for decades, enabling advanced multitasking operating systems and more powerful software applications. The chip's success solidified Intel's market leadership and set the stage for the modern computing era.

History and development

Development of the 80386, codenamed "P3", began in 1982 under the leadership of Intel engineers like John H. Crawford and Patrick Gelsinger. The project aimed to create a true 32-bit successor to the Intel 80286 while maintaining backward compatibility with the vast library of x86 software. A key decision was to implement a memory management unit on-die, a significant advancement over earlier designs. The first samples were delivered to partners like Compaq and the chip officially launched amidst competition from processors like the Motorola 68020. Its development was a massive undertaking for Intel, involving new semiconductor fabrication techniques at facilities such as its D1 and D2 plants.

Architecture

The 80386 featured a full 32-bit architecture, with 32-bit general-purpose registers, a 32-bit external data bus, and a 32-bit address bus, enabling access to up to 4 gigabytes of physical memory and 64 terabytes of virtual memory. Its integrated memory management unit supported sophisticated paging and segmentation. The processor used a pipelined execution unit to improve performance, fetching and decoding instructions in stages. It also introduced a hardware debug register set. The internal design was partitioned into a Bus Interface Unit, a Code Prefetch Unit, a Decode Unit, and an Execution Unit, coordinating operations for the new 32-bit instruction set.

Operating modes

The processor introduced three primary operating modes: real mode, protected mode, and virtual 8086 mode. Real mode provided full backward compatibility with earlier x86 processors like the Intel 8086, but without memory protection. Protected mode was the native 32-bit state, enabling the memory management unit, virtual memory, and hardware-enforced task isolation crucial for systems like Microsoft Windows NT and IBM OS/2. Virtual 8086 mode was a sub-mode of protected mode that allowed the processor to run multiple legacy DOS programs in isolated virtual machines, managed by a supervising operating system kernel.

Variants and derivatives

The original 80386DX, with a full 32-bit external bus, was joined in 1988 by the lower-cost 80386SX, which had a 16-bit external bus to allow cheaper system designs. Intel also produced the 80386SL, which integrated power management and cache controller logic for the burgeoning laptop computer market. Key second-source manufacturers included AMD, which produced its Am386 line after a prolonged legal battle with Intel, and IBM, which manufactured chips for its own PS/2 systems. Other derivatives included the 80386EX, used in embedded systems, and chips from companies like Cyrix and Chips and Technologies.

Impact and legacy

The 80386 was instrumental in the transition from 16-bit to 32-bit computing, becoming the foundation for a generation of IBM PC compatible systems. It enabled the development and success of 32-bit operating systems including Microsoft Windows 3.0, Windows NT, Linux, and BSD Unix variants. The architecture defined by the 80386 evolved directly into the Intel 80486, the Pentium series, and modern x86-64 processors. Its design principles influenced subsequent microprocessor development across the industry, cementing the x86 architecture's dominance in desktop and server markets for generations.

Category:Intel microprocessors Category:1985 introductions Category:X86 microprocessors