The general idea is that microcomputers are about microprocessors (MPUs), which combine a CPU, consisting of an ALU, internal registers and bus logic (and maybe some port registers) in a single chip. Generally, the 4-bit Intel 4004 is considered to be the first commercial microprocessor, soon followed by the 8-bit Intel 8008.

The Intel 8008 was actually begun before the 4004 and implemented the design of an earlier, discrete component processor (of the Datapoint 2200 from 1969) as a microprocessor. (This project was initiated by the Computer Terminal Corporation, AKA Datapoint, who comissioned a microprocessor implementations of their processor to Intel, Fairchild and Texas Instruments. The Intel project was the only one to succeed, but the implementation was rejected for being already outdated and too slow at the time, leaving Intel with rights to the design. The rest is history…)

Generally, early coin-op video games, like Computer Space, Gotcha, Space Race, or Pong are not considered microprocessor based, they even lack a CPU in the stricter sense. They are really just somewhat more complex video pattern generators, at least, this is what Nolan Bushnell called them – and he ought to know ;-).

(These early games lack any stepping logic, apart from single-directionally progressing counter chains, which drive discrete TTL logic, which in turn produces the video signal. Movement is exclusively effected by presets to these counter chains and gameplay, like object collisions, is determined by simple logic gates, based on the state of these counter chains. There is nothing Turing-complete in this logic. Commonly, Tank is considered the first coin-op game to use any large scale integrated logic at all (masked ROMs for sprite data instead of discrete diode matrices) and Western Gun, AKA Gun Fight (US-release in 1975) to be the first arcade video game to be based on a microprocessor.)

Regarding the Pentium II – well, that's a tricky question. There are a few contenders to the title of the first microprocessor, even predating the i4004 (e.g., the Four-Phase Systems AL1 from 1969,) the claims of which are generally rejected for not containing the entire processor in a single chip (but two or three of them). Following this logic and tradition, we had to reject the Pentium II, as well. However, due to another, completely unrelated marketing tradition, we commonly do consider the Pentium II to be a MPU.