Evolution

The 4004 was the forerunner of all of today's Intel offerings and, to date, all PC processors have been based on the original Intel designs. The first chip used in an IBM PC was Intel's 8088. This was not, at the time it was chosen, the best available CPU, in fact Intel's own 8086 was more powerful and had been released earlier. The 8088 was chosen for reasons of economics: its 8-bit data bus required less costly motherboards than the 16-bit 8086. Also, at the time that the original PC was designed, most of the interface chips available were intended for use in 8-bit designs. These early processors would have nowhere near sufficient power to run today's software.

The table below shows the generations of processors from Intel's first generation 8088/86 in the late 1970s to the eighth-generation AMD Athlon 64, launched in the autumn of 2003:

Type/ Generation	Year	Data/ Address bus width	Level 1 Cache (KB)	Memory bus speed (MHz)	Internal clock speed (MHz)
8088/ First	1979	8/20 bit	None	4.77-8	4.77-8
8086/ First	1978	16/20 bit	None	4.77-8	4.77-8
80286/ Second	1982	16/24 bit	None	6-20	6-20
80386DX/ Third	1985	32/32 bit	None	16-33	16-33
80386SX/ Third	1988	16/32 bit	8	16-33	16-33
80486DX/ Fourth	1989	32/32 bit	8	25-50	25-50
80486SX/ Fourth	1989	32/32 bit	8	25-50	25-50
80486DX2/ Fourth	1992	32/32 bit	8	25-40	50-80
80486DX4/ Fourth	1994	32/32 bit	8+8	25-40	75-120
Pentium/ Fifth	1993	64/32 bit	8+8	60-66	60-200
MMX/ Fifth	1997	64/32 bit	16+16	66	166-233
Pentium Pro/ Sixth	1995	64/32 bit	8+8	66	150-200
Pentium II/ Sixth	1997	64/32 bit	16+16	66	233-300
Pentium II/ Sixth	1998	64/32 bit	16+16	66/100	300-450
Pentium III/ Sixth	1999	64/32 bit	16+16	100	450-1.2GHz
AMD Athlon/ Seventh	1999	64/32 bit	64+64	266	500-2.2GHz
Pentium 4/ Seventh	2000	64/32 bit	12+8	400	1.4GHz-3.6GHz
AMD Athlon 64/ Eighth	2003	64/64 bit	64+64	400	2GHz-2.4GHz