This article relates to the fractal program "Apophysis" (Apo), but may also be relevant to other image rendering programs.
In Apo, there is a setting in the OPTIONS menu where one can specify the number of rendering "threads" to use. This has a direct impact on the amount of rendering time an image takes to render. If set to OFF, the image will render as if it was using a single CPU. If set to 2 or 4, the image will render in much less time, because it has 2 or 4 CPU cores of which to take advantage.
People who have Intel CPUs, which have hyperthreading (such as some Pentium 4's), can set this option to 2 if they wish (DO NOT use higher than 2).
Don't know how to get an image in here, so here is the screenshot link showing this setting option. www.deviantart.com/deviation/4…
Hyperthreading (wanky marketing speak), basically means the CPU has "two threads" with which to perform its data processing (sort of like two CPUs). When set to 2, Apo can use 100% of the CPU and thus cut rendering time. However, this may not be the best option with systems which generate a lot of heat and are not efficiently cooled (some laptops/notebooks may be an issue). It can be a trade-off between less render-time, OR a processor working at half its capacity and therefore producing less heat. System crashes can be a result of the processor over-heating.
If you have a newer system with either an AMD or Intel Dual-core processor, or for those fortunate people who may have a quad-core, then you should definitely set this option to correspond with the number of cores in your processor. There should be no problem with over-heating, as these newer processors have more efficient thermal designs than the older Pentium 4's.
I am running a Pentium 4 which has hyperthreading and I have set the multithreading option to 2. It can sometimes halve the rendering time, but always results in a substantial reduction.
The other thing I notice is the drop-down box below the multithreading box, which relates to both your CPU and operating system. Newer CPUs (from around mid-2003 for AMD and later for Intel) are 64bit. Prior to this they were 32bit. If your CPU and operating system are both 64bit, then I also suggest choosing the 64bit setting. I don't know the impact of this (mine is 32bit), but you will find out once you switch between the 32 and 64bit settings.
Here is the screenshot link showing this setting option. www.deviantart.com/deviation/4…
To test the impact of changed settings, you need to commence a render on the old settings. At the bottom of the render screen, the "estimated time to complete" will appear. Take note and STOP the render, then close it. Go back into OPTIONS and change the settings then commence the same render. Now you should see the time to complete has considerably reduced.