The ATmeg328 is a low-power CMOS 8 bit microcontroller based on AVR enhanced RISC (Reduced Instruction Set Computer) architecture. the ATmeg328p achieves throughput approaching 1 MIPS (Millaion Instructions per Second) per MHz allowing the system designer to optimize power consumption versus processing speed. Datasheet document contains all the specs of the chip, from functionality to assembly point of view. It has been officially released by Atmel. Under given is a pdf version atmega328 datasheet.
Some people also search for atmega 328p datasheet with following words, Current datasheet serves for all of these queries.