Some numbers from an AT member worthy of a read :
http://www.anandtech.com/show/7933/the-desktop-kabini-review-part-1-athlon-5350-am1/3Here in Germany the J1900 became available before the J1800 at my favorite retailer: I got a GIGABYTE GA-J1900N-D3V (quad core) some weeks ago, put it into a mini-ITX case with a 90Watt PicoPSU (needed the 12V 4pinconnector) and a 60Watt 12V notebook power supply.
Added a Crucial C300 for storage and went ahead testing with Window 8.1 (the only thing that worked with the initial BIOS) and then with Win7, CentOS 6.5, Fedora 20, Android x86 after the new BIOS made that possible.
Did the same with a GIGABYTE GA-J1800N-D2H (dual core) two weeks later and benched them side by side.
First off, both CPUs *always* work at their top speeds unless idle. So that's 2.41GHz for the J1900 and 2.58GHz for the J1800. The nominal speeds aren't ever used, and I guess their main reason for existance is because it make them look nicer in the Intel charts. And perhaps their predecessors were actually fixed clocked at that value and I guess you'd still get those if you disable turbo in the BIOS.
Again, even running a Prime95/Furmark combo for hours, won't get any of these CPUs to drop their speeds to nominal: Turbo speeds aren't just for single threaded loads.
That mainly means that the normal clock difference between the J1900 and the J1800 isn't all that big, just 170MHz on the CPU, while the GPU on the J1900 is a notch above the J1800.
That again means, that the main difference between the two is the number of cores (2 vs. 4) and the amount electricity they consume and turn into heat.
It doesn't matter in terms of normal office applications or browsing: The J1800 typically came 170MHz out ahead on things like Kraken or Octane and both are fast enough at 1080p for most users. Yes, side by side with a top-notch 100Watt desktop CPU they are a tad slower, but nothing to loose hair about: Again not-an-Atom any more!
I managed to get the J1800 to 6.3Watts at the power outlet (behind the 60Watt AC/DC and the 12V PicoPSU) with 8GB of LV DRAM, the Crucial SSD, video off on a 64-Bit Windows 8.1 idle desktop. The J1900 will take 3 Watts more (9.3) for the same setup, which seems to indicate that one half of the J1900 can't go to C7 if the other one is still more or less awake.
There is of course also another Ethernet port, more USB 3.0 but none of them were used during the low-power tests.
On the other end, a combined Prime95 and FurMark will result in 28Watts on the J1900 and in 22Watts on the J1800. Core power consumption measured via CPUIDs HWMonitor showed 2.29Watts for the J1900 cores and 2.4Watts for the J1800 cores, while the package consumption was put at 6.85Watts for the J1900 vs. 6.54Watts for the J1900.
This oddity was consistent and I can only explain it by HWMonitor only measuring one of the two CPU blocks on the J1900, but the full GPU block (and remainder of the SoC), which is clocked a little higher on the J1900 under load.
The passive cooling solution on the Gigabyte J1900 board was not capable to dissipate all the generated heat on the Prime95/Furmark combination which generated 28Watts at the socket. About 30 minutes into the test at the threshold temp set in the BIOS (I used 90°C) the CPU started to throttle to 1.3GHz and went back to 2.41GHz once the temperature sank sufficiently.
The J1800 never reached or exceeded 50°C under the same load.
That all points at the 10W TDP as bolloks or only valid for nominal CPU clocks, but I'm not going to complain, because under any normal or reasonable load, even the J1900 never throttles.