HFat wrote:Even an underclocked dual-core Sandy Bridge woudn't be twice as fast as a dual-core desktop Atom.
I read that and thought it couldn't be right. I own and/or work with several Atom based systems and Sandy Bridge ones and the SBs are much, much faster even when under clocked. But before making any solid claims I went and tested myself.
Unfortunately I didn't have any SB machines I could run tests on (maybe on the weekend), but I did have an i870. Unless there is some really weird corner case, a SB should be faster per-clock than a i870.
I ran the tests on FreeBSD, with the unixbench program. FreeBSD can lock a CPU to any supported speed-step speed, so I was able to get the clocks as close as possible. Unixbench is completely single threaded, so the i870 being quad core gave it no benefit over the dual core Atom.
So, a 1.66 GHz Atom 510 VS a 1.60 GHz i870 per core:
Integer: 328.7 vs 923.1, 2.8X faster
Floating point: 143.4 vs 387.3, 2.7X faster
So the under clocked i870 is close to 3X the speed of the Atom. A SB under clocked to 1.6 GHz would be even faster.
To put it another way: to match the Atom I had to drop the i870 to approx 600 MHz. That's a serious under clock.
I acknowledge that this is a purely CPU benchmark and that the rest of the system components may make a big difference.
As a point of comparison more relevant to this thread, a 1.5 GHZ P4 Prescott (closest I could get to 1.66) is 371.4 / 151.8, or about 1.1X faster than the atom.