What does SOC usually have?

System-on-a-chip or system on chip (SoC or SOC) refers to integrating all components of a computer or other electronic system into a single integrated circuit (chip). Usually it consists of

• One microcontroller, microprocessor or DSP core(s). Some SoCs – called multiprocessor System-on-Chip (MPSoC) – include more than one processor core.
• Memory blocks including a selection of ROM, RAM, EEPROM and flash.
• Timing sources including oscillators and phase-locked loops.
• Peripherals including counter-timers, real-time timers and power-on reset generators.
• External interfaces including industry standards such as USB, FireWire, Ethernet, USART, SPI.
• Analog interfaces including ADCs and DACs.
• Voltage regulators and power management circuits.

Reference:
http://en.wikipedia.org/wiki/System-on-a-chip