Power consumption and integrating a processor into portable or embedded devices have always caused problems for Intel, and this is not the first time the company has offered processors aimed at those uses. But the Atom is radically different in that it has a new architecture specially created to reduce power use.
A Short History: Before the Pentium-M
As far back as the 80386, Intel offered versions intended for low power and especially mobile use. The 80386EX, for example, had a chipset built into the CPU and consumed significantly less power than standard 386s. And low-power versions of the 486, the Pentium, and the Pentium II (the Dixon, with its 256 kB of built-in cache) were also offered. And yet in every case they essentially used a very similar (if not identical) architecture to the one used in the desktop version of the processor. In practice, these processors were efficient, but the difference between a standard version and a version for portable PCs remained slight.
Released in 2003, the Pentium-M was revolutionary in that it used a different architecture from that of the Pentium 4 and consumed much less power, while maintaining high performance. Yet it was still a derivative of the Pentium III, with the same faults, and the successive improvements to the Pentium-M (leading up to the Core 2 processors) have only increased power consumption. Intel has tried to come out with low-power processors (the A1x0, for example), but essentially they were slowed-down versions of the Pentium-M.
Atom Changes All of That
Atom is a different architecture in the sense that it was designed to reduce power consumption and that the processor uses a totally new design. It isn’t an adaptation of an earlier architecture. Concretely, Intel is now able to offer processors that consume very little power – the high-end Atoms consume less power than the (generally very slow) ULV versions of the standard architectures.