i386

The i386, short for Intel 80386, is a 32-bit microprocessor and the first member of the i386 family of the x86 architecture. Introduced in 1985, it extended the 16-bit x86 lineage with 32-bit data and address sizes and introduced protected mode with paging, enabling modern multitasking and virtual memory.

Technical features include eight 32-bit general-purpose registers (EAX, EBX, ECX, EDX, ESI, EDI, EBP, ESP), an instruction pointer (EIP), and a 32-bit EFLAGS register. It supports both segmentation and paging for memory management, with the Global Descriptor Table and Local Descriptor Tables, four privilege levels (rings 0–3), and a 4 GB virtual address space. The architecture supports transitions between real mode and protected mode and laid the groundwork for flat memory models and virtual memory systems that followed.

The i386 established the baseline for 32-bit software on PC hardware and remains influential through its descendants. It defined the 32-bit instruction set and programming model that is retained by x86 processors, and in operating systems and software packaging, “i386” is commonly used to denote 32-bit x86 builds. Today, many processors provide an i386 compatibility mode in 64-bit environments, allowing 32-bit code to run on modern hardware.

Legacy remains strong: while surpassed by the 64-bit x86-64 architecture in terms of address space and performance, the i386 lineage continues to support legacy applications and embedded systems. Its instruction-set heritage persists in contemporary CPUs and software ecosystems.