Ultra low power Nehalems on an Asus Z8NA-D6 mainboard

WITH ALL THE 'GREEN' energy saving focus these days, it's no wonder that the GigaFLOPS and Gigabytes numbers are now joined by Watts figures too.

Except, in the case of Watts, the lower the better. The recent crop of high end workstation, server and desktop processors have both high performance and good power performance options. For instance, for the Nehalem-EP, the same D stepping design can be either a high powered W5590 3.33GHz processor with a 120W power envelope or an ultra low power L5530 2.4GHz processor with a 50W power envelope. So, 33 per cent more speed for 2.4 times higher TDP, but you have a choice depending on your needs. Both have the same large caches, three-channel memory per CPU and QPI links, but very different power and performance profiles.

Here we have a look at one such configuration. I put together two of these L5530 Nehalem Xeons on the Asus Z8NA-D6 mainboard, a very unique ATX-sized dual CPU mainboard with all six memory channels, one DIMM per channel. Now, with proper design tuning, that could really reduce the round-trip latencies on each channel. The mainboard is not a typical reference design, but reworked using solid capacitors and tighter traces to fit everything needed within the ATX format. Now, there are no extra bells and whistles that its Harpertown 5400 chipset predecessor, the Z7S-WS, had. Heat pipes on the chipset or overclocking features are not seen here at all, unfortunately. Nevertheless, the Z8NA-D6 mainboard, with its spread of features including on-board SAS with a hardware RAID option, does impress. And, oh yes, it accepts desktop memory without problems.

Speaking of the memory, I also used the Geil very low voltage DDR3 memory that we tested before on the Gigabyte X58 and P55 platforms. Its DRAM sticks are officially declared as 1.3 volts but run fine at 1.2 volts. With the Asus Z8 mainboard option to force 1.2V memory in hardware, it was a piece of cake. The memory ran and passed all tests at 1.2 volts, including Sandra benchmarks, Linpack and 3DMark Vantage. It would be interesting if Geil was to put out an ECC version of this memory.

The mainboard does have integrated basic graphics, but of course I wanted to pair it up with a good piece of graphics hardware - in this case, the ATI Radeon 5870, currently the fastest single GPU platform around. Then, to measure the power load as it really is, I put the trusty old MGE 500W power supply with its own LCD display showing the power usage in place.

What was the measured power consumption, then?

The first test was the platform itself using integrated graphics, no mass storage or such complications. Boot to BIOS and mess around with it, and the PSU showed a consistent 92W to 96W total. Again, this is a dual processor, 8-core 16 thread platform. Not bad at all. But then, what happens when you add an A-Data XPG 64GB SSD as well as the ATI HD5870 card, and then boot Vista?

The power consumption jumped to a still respectable 164W at boot time, but then dropped down to about 138W to 145W when running Vista, as the GPU's power saving features kicked in. Then I ran the 3DMark Vantage benchmark. Of course the power draw jumped, but across all the tests the highest power consumption for the whole system I recorded was 189W. This is half the consumption of the similar W5590 dual Xeon configuration and, guess what, 30 per cent less than the similar setup with default speed AMD Phenom II 965 BE processors.

But then, AMD has the 6-core Istanbul at 1.8GHz, which I found to be in the same power envelope as these Nehalems. However, per core, running actual applications the Nehalem will be up to twice as fast, so using 4-core Shanghai chips with higher core clocks in a similar power envelope might be more appropriate.

Performance wise, it's pretty much one third off the W5590 scores across the board, as CPU, cache and memory speeds are all proportionally slower. For illustration, above is the Sandra CPU benchmark result. Not a bad result for a low power compact ATX system. µ

Good: Great 8-core performance at midrange desktop power consumption.

Bad: These chips are still priced at 800 bucks a pop.

Ugly: Can't run the memory at DDR3-1333 due to the slower uncore (but who cares with six channels?).

Beers: 9/10