HTPC Power Consumption

We tested the claim that you need a quad core for the best HTPC. In fact I'll be using my own home theatre PC as a reference:

• AMD Athlon X2 4850e (2x2.5GHz, 1.0GHz HTT),
  
• Gigabyte GA-MA78GM-S2H motherboard (F5 BIOS)
  
• 2GB OCZ PC2-6400 memory (4-4-4-12-2T)
  
• 250GB Samsung Spinpoint Hard Drive
  
• Corsair VX550W PSU
  
• EMU EM8852 PCI Soundcard
  
• Pioneer BDC-SO2BK Blu-ray Drive

The PC has been loaded with Vista 32-bit SP1, including Media Center Edition and Cyberlink's PowerDVD 8 Ultra for Blu-ray support. In addition, given the excellent guide by forum member, Busterboo, we also upgraded to the latest edition of Media Player Classic - Home Cinema (MPC-HC) to enable High-Definition GPU acceleration for file formats like mkv, which PowerDVD doesn't support.

We are currently working out a bug with the Gigabyte board that meant we couldn't enable Cool'n'Quiet. Usually the process is to enable the function in the BIOS and set Vista to either Power Saving or Balanced so that the CPU will automatically throttle down under low load conditions. However, no matter what BIOS or Catalyst driver we tried, we couldn't get the processors to work outside of their default speeds. If you can get CnQ working, remember you'll save a little bit more power under idle conditions.

We tested under the following conditions:

• The system was left idle on the Windows desktop,
  
• It was loaded with Prime95 torture test on all cores
  
• It was loaded with a 1080p MKV x264/DTS video file using MPC-HC and the EVR renderer to take advantage of GPU acceleration on AMD's 780G IGP.
  
• It was loaded with a 1080p MKV x264/DTS video file using VLC using just the CPU for video and audio decoding
  
• Casino Royale Blu-ray disc playback using PowerDVD 8 Ultra and GPU acceleration turned on.

We believe these are some typical scenarios that you would find yourself using your HTPC in - but do you need a quad-core? Or is a faster dual-core more power efficient? The Athlon 64 X2 4850e is also a 45W CPU so surely if you can get away with a lower power, lower cost processor this will be obviously beneficial.


As is expected, we can see from the results the 65W quad-core obviously uses more power than the 45W dual-core - some 20W at idle (remember CnQ wasn't working properly for us though), and 20-to-30W more during GPU accelerated playback.

For the CPU accelerated 1080p playback, we were still unable to get it smooth. Unfortunately VLC and even Vista MCE would run both up to a point of very high bitrate then one of the cores would simply hit full load and it would stutter playback. This is simply a codec-software issue, obviously if it was more threaded there would be overhead available. On both the 4850e and 9350e, the playback sat at around 30-40 percent on all cores, regardless of whether there were two or four available.

We changed to use the CoreAVC codec (under Haali's Media Splitter in MPC-HC output options) and found this worked much better with the 9350e, averaging 35-45 percent with spikes to 60-70 percent equally over all four cores. The playback was perfectly smooth, and the power usage not too bad at just 105W. In comparison when we tried the 4850e the power consumption was only slightly less at 98W but the loading on both cores was 95-100 percent. The playback was not watchable as it constantly stuttered.

In conclusion, we have to say that GPU off-loading with a lowest power CPU is clearly the best option, but under certain conditions we realise this can't be used. Given our experiences we'd love to recommend the quad-core as the next default choice - for only a few watts more you get more efficient smooth playback, but only on condition that the software is written to take advantage of it. If it isn't and it's either single threaded or lightly threaded then we're back to needing a faster single/dual-core CPU again.