

Inside Intel's New Chip - Atom - kungfudoi
http://www.technologyreview.com/printer_friendly_article.aspx?id=20525

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reitzensteinm
Atom is very impressive. Intel demonstrated it running Unreal Tournament 2k3 +
Vista on Atom + its chipset (integrated graphics), without so much as a
heatsink on either.

Unfortunately, the chipset is still etched on 130nm and is substantially
bigger than Atom itself - you won't find the combination in an iPhone any time
soon.

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mullr
I don't quite understand how hyperthreading saves power. Is it better than
doing OOO execution because there's less hardware required? I could imagine
that instructions targeted at two virtual CPUs could be interleaved more
simply and flexibly.

~~~
reitzensteinm
It doesn't save power in absolute terms (which is why the lower power Atom
chips disable it), but it increases performance per watt (and performance per
transistor). Basically, on modern chips the leakage power is a huge proportion
of the total power used, so you're paying for blocks of logic whether you're
using them or not. You can shut off blocks (most modern processors do this),
but only at a very granular level.

Hyperthreading runs two threads simultaneously, and when one thread stalls,
the other thread takes over, so you get a much higher % utilization of the
chips resources. Switching power used goes up, leakage stays the same, and
performance increases.

Hyperthreading speeds up simple, in order chips like the Atom particularly
well (because a single thread is stalling so much!). So don't expect
equivilant performance gains from Nehalem hyperthreading.

