Intel 80386SX

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Intel 80386SX

The 80386SX is a "lite" version of the 80386DX chip. It uses only a 16-bit data bus, the same external bus width as the 80286. It also only can address 16 MB of memory, like the 80286. The SX version of the 386 chip was in fact released well after the DX, and in some ways was intended to move the market away from the 286 since it had roughly the same interfaces but better performance. It was actually introduced several years after the DX.

Note: It is a common myth that the 80386SX can be substituted in place of an 80286 in a 286 motherboard. While the chips are compatible in terms of their external interfaces they use different packaging. A 386SX could be put into a 286 motherboard if a proper adapter were used.

The narrower data bus width of the 386SX creates a reduction in performance of about 20-25% compared to an equivalent-speed 386DX; a significant difference but not excessive. The 80386SX chip was a popular choice for the first small notebook computers, especially the 386SL variant that introduced the SMM power management features to the Intel line. The 386SX is still a 32-bit processor internally and will run 32-bit software (really slowly :^) ). It is available in speeds from 16 to 33 MHz; a 40 MHz version was not produced for the SX, and is also available in cloned versions from AMD and Cyrix.

The 386SX chip is today considered obsolete.

Look here for an explanation of the categories in the processor summary table below, including links to more detailed explanations.

General Information	Manufacturer	Intel, AMD, Cyrix
	Family Name	80386SX
	Code name	"P9"
	Processor Generation	Third
	Motherboard Generation	Third
	Version	80386SX -16	80386SX -20	80386SX -25	80386SX -33
	Introduced	June 1988	Jan. 1989	June 1988	Oct. 1992
	Variants and Licensed Equivalents	386SL (power management features)
Speed Specifications	Memory Bus Speed (MHz)	16	20	25	33
	Processor Clock Multiplier	1.0
	Processor Speed (MHz)	16	20	25	33
	"P" Rating	--
Benchmarks	iCOMP Rating	22	32	39	56
	iCOMP 2.0 Rating	--
	Norton SI	~11	15	~20	~27
	Norton SI32	!?
	CPUmark32	--
Physical Characteristics	Process Technology	CMOS
	Circuit Size (microns)	Originally 1.5, now 1.0
	Die Size (mm^2)	!?
	Transistors (millions)	0.275 (0.855 for 386SL)
Voltage, Power and Cooling	External or I/O Voltage (V)	5
	Internal or Core Voltage (V)	5
	Power Management	SMM on 386SL only
	Cooling Requirements	None
Packaging	Packaging Style	132-Pin PGA
	Motherboard Interface	132-Pin Socket
External Architecture	Data Bus Width (bits)	16
	Maximum Data Bus Bandwidth (Mbytes/sec)	31.8	38.1	47.7	63.6
	Address Bus Width (bits)	24
	Maximum Addressable Memory	16 MB
	Level 2 Cache Type	None
	Level 2 Cache Size	--
	Level 2 Cache Bus Speed	--
	Multiprocessing	No
Internal Architecture	Instruction Set	x86
	MMX Support	No
	Processor Modes	Real, Protected, Virtual Real
	x86 Execution Method	Native
Internal Components	Register Size (bits)	32
	Pipeline Depth (stages)	4
	Level 1 Cache Size	None
	Level 1 Cache Mapping	--
	Level 1 Cache Write Policy	--
	Integer Units	1
	Floating Point Unit / Math Coprocessor	Optional 80387 Coprocessor
	Instruction Decoders	1
	Branch Prediction Buffer Size / Accuracy	None
	Write Buffers	None
	Performance Enhancing Features	None

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