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The predecessor of the 80386 was the Intel 80286, a 16-bit processor with a segment-based memory management and protection system. The 80386 added a three-stage instruction pipeline which it brought up to total of 6-stage instruction pipeline, extended the architecture from 16-bits to 32-bits, and added an on-chip memory management unit. [21]
The primary defining characteristic of IA-32 is the availability of 32-bit general-purpose processor registers (for example, EAX and EBX), 32-bit integer arithmetic and logical operations, 32-bit offsets within a segment in protected mode, and the translation of segmented addresses to 32-bit linear addresses. The designers took the opportunity ...
386—Intel 80386 processor; 486—Intel 80486 processor; 4B5BLF—4-bit 5-bit local fiber; 4GL—fourth-generation programming language; 4NF—fourth normal form; 5GL—fifth-generation programming language; 5NF—fifth normal form; 6NF—sixth normal form; 8B10BLF—8-bit 10-bit local fiber; 802.11—wireless LAN
The boards allowed users to upgrade their machines' CPU to a 16 MHz 80386 processor. Both variants utilized a ribbon cable which plugged into the computer's original CPU socket on one end and into a socket on the Inboard card on the other end. Both boards were full-length ISA expansion cards and occupied one slot.
The 80386 also introduced two new general-purpose data segment registers, FS and GS, to the original set of four segment registers (CS, DS, ES, and SS). A 386 CPU can be put back into real mode by clearing a bit in the CR0 control register, however this is a privileged operation in order to enforce security and robustness.
The 8088 version, with an 8-bit bus, was used in the original IBM Personal Computer. 186 included a DMA controller, interrupt controller, timers, and chip select logic. A small number of additional instructions. The 80188 was a version with an 8-bit bus. 286 first x86 processor with protected mode including segmentation based virtual memory ...
With the introduction of the 80386 processor, Intel began introducing "experimental" features that would not necessarily be present in future versions of the processor. The first of these were two "test registers" (TR6 and TR7) that enabled testing of the processor's translation lookaside buffer (TLB); a special variant of the MOV instruction allowed moving to and from the test registers. [1]
The 80386 had an optional floating-point coprocessor, the 80387; it had eight 80-bit wide registers: st(0) to st(7), [33] like the 8087 and 80287. The 80386 could also use an 80287 coprocessor. [34] With the 80486 and all subsequent x86 models, the floating-point processing unit (FPU) is integrated on-chip.