[mpw222]

I have a pair of PCs running XBMC, an XP HTPC and my Vista desktop. One thing I've noticed is that the XP box seems to have some kind of floor for CPU usage. Even on files that should take a minimal amount of power to decode (640x360 xvid) CPU usage is north of 40%. This doesn't seem to be the case on my Vista box, where the same file results in single digit CPU usage.

The situation is the same with very demanding content. For instance the birds clip takes no more than 40% of CPU power on the desktop, but 95+% on the HTPC. Normalizing for the number of cores and the clockspeed (I know things don't quite work this way) that means it takes over 6.8GHz of power to decode birds in XP, but only 5.1GHz of power on Vista. The HTPC even has some advantages like being a 45nm Penryn, not a 65nm Kentsfield (there are minor tweaks that help IPC) a faster bus (1600 vs 1400) and more memory bandwidth (800 vs 700MHz, similar timings). On top of that the HTPC is a barebones install with very few services and background processes vs. the desktop, which has a ton of stuff on it (not to mention Vista's overhead vs. XP). Any thoughts?



HTPC
XP SP3
Core 2 Duo [email protected]
Geforce 9500GT w/ nVidia 180.48 drivers
2GB DDR2 800
1080i60 or 1080p24

Desktop
Vista x64 SP1
Core 2 Quad [email protected]
Geforce 8800GTX w/ nVidia 180.48 drivers
8GB DDR2 700
1920x1200

[cold_realms]

The first thing that comes to mind is that Vista is MUCH better suited to run on multi-core CPU's than XP. In my own testing Vista runs 5-25% faster on the exact same hardware. (testing done prior to SP1 when I was still dual booting to XP). I also remember reading something about multi-core cpu optimizations in vista but you will have to google that one .

[mpw222]

The first thing that comes to mind is that Vista is MUCH better suited to run on multi-core CPU's than XP. In my own testing Vista runs 5-25% faster on the exact same hardware. (testing done prior to SP1 when I was still dual booting to XP). I also remember reading something about multi-core cpu optimizations in vista but you will have to google that one .

The core OS does make better use of multiple cores (it also does a lot more in the background), but there should be relatively little impact on actual applications, especially when we're talking about 2 and 4 core systems. NT has always had reasonable support for multi-CPU systems. Even with the huge low level differences in the XP and Vista kernels, the gap I'm seeing seems way bigger than that might explain.

A little off topic, but my experience has been that single tasks rarely run more quickly in Vista, but the overall experience is often better provided you throw a lot of memory at it. Video encoding with x264 for instance is defintiely not faster in Vista.

[cold_realms]

The core OS does make better use of multiple cores (it also does a lot more in the background), but there should be relatively little impact on actual applications, especially when we're talking about 2 and 4 core systems. NT has always had reasonable support for multi-CPU systems. Even with the huge low level differences in the XP and Vista kernels, the gap I'm seeing seems way bigger than that might explain.

A little off topic, but my experience has been that single tasks rarely run more quickly in Vista, but the overall experience is often better provided you throw a lot of memory at it. Video encoding with x264 for instance is defintiely not faster in Vista.

Each to his own. When i moved fully to vista I tested in everything i could think of. Games, music ripping, Video encoding (xvid), productivity, etc...

There was no instance where XP was faster.