A summary of microprocessors used in PCs
8086
16 bit internal data bus.
16 bit external data bus.
20 bit address bus.
Data and address bus are multiplexed.
80186
16 bit internal data bus.
16 bit external data bus.
20 bit address bus.
8086 with integrated RAM refresh, DMA controllers, Interrupt controllers, Timers, Additional instructions.
80286
16 bit data bus.
24 bit address bus.
Two processor modes:
Real mode - 8086 compatible.
Protected mode - uses full 24 bit address space addressed in 64 kbyte segments.
80386DX
32 bit internal data bus.
32 bit external data bus (DX: Double-word eXternal).
32 bit address bus.
Three processor modes:
Real mode - 8086 compatible.
Protected mode - uses full 32 bit address space.
V86 mode - simulates multiple 8086's.
80386SX brought out later - has:
32 bit internal data bus.
16 bit external data bus (SX: Single-word eXternal).
24 bit address bus.
80486DX
32 bit internal data bus.
32 bit external data bus.
32 bit address bus.
80386DX with 8K Cache, improved execution with pipelines and branch prediction, Integrated numeric co-processor, Additional instructions.
80486SX brought out later which has co-processor disabled. The addition of a 487 co-processor in fact disables the 486SX and replaces it.
80486DX2 is internally clocked at double the speed of the external motherboard clock.
80486DX4 is clocked at triple the speed.
Pentium
32 bit internal data bus.
64 bit external data bus.
32 bit address bus.
Translation between internal and external data buses is via a memory management unit and an 8K data cache.
Features: 80486 instruction compatible, pipelined co-processor, pipelined execution in cpu, branch prediction, 8K instruction cache, multiprocessor support.
Pentium Pro
As Pentium but
256 kbyte level 2 cache, instruction pool, multiple branch prediction, data flow analysis, speculative execution.
Pentium with MMX
MMX = multimedia instructions such as 3D bitmap manipulations.