What is the best processor for rendering - i5 or i7

The answer depends on the number of cores and the processing speed.

Here are 6 processor/speed combinations currently available for a Dell Precision T1500. (Speed is determined by # cores X core speed)

The fastest I7 quad would be almost twice as fast for rendering than the slowest dual I5. (The column labelled Render Speed should have said Rendering Time)

However, it would not be faster when running SketchUp, and would not be faster when extracting the data for rendering, etc.

Also, the video card does not effect rendering speed for IRender nXt.

▶ Reply to This

Replies to This Discussion

Permalink Reply by Render Plus on September 22, 2010 at 9:39am

Let me add,

4GB of RAM is plenty for rendering.

The video card does not effect rendering speed.

Assuming you have 4GB RAM, then the number of cores times the procesor speed is the controlling factor.

▶ Reply

Permalink Reply by Paul Davis on March 3, 2011 at 4:23pm

Al, your chart doesn't mention hyperthreading. does the i7 hyperthreading make any difference? i7 has 4 cores and 4 virtual hyperthread cores(meaning 8 total cores). So an i7 870 should be 8 x 2.93 = 23.44. Has any tested an i7 and seen if all 8 cores are at work?

▶ Reply

Permalink Reply by Chip Stapleton on June 7, 2011 at 9:28am

Any news on hyperthreading and iRender?

▶ Reply

Permalink Reply by Roy Hirshkowitz on June 7, 2011 at 11:27am

The short answer is that hyperthreading may help a little, but not a lot. Intel estimates 30% improvement-- I seriously doubt you'll get half of that.

The longer answer goes something like this: hyperthreading is not the same as multi-core. It replicates some pieces of the core but not the execution unit or memory caches. It may relieve some bottlenecks but tends not to help too much with apps. that are highly processor and memory bound, such as nXt.

Here's more if you really want it:

When I ask Windows Vista or Windows 7 how many procs it has it is supposed to report physical procs-- not virtual ones. I have not verified this behavior-- and it's a little ambiguous in the documentation. In any case, nXt by default creates two worker threads per physical procs. which should be ideal for hyperthreading-- however-- I know Al was messing around with this setting and may have changed it. This may require user input to increase the max allowed worker threads.

When I ask Windows XP (pre SP3) the same question, it reports the number of logical processors. This means that even if Al has set the default behavior to be one worker thread per proc.-- hyperthreaded pre-SP3 XP boxes will not require any additional intervention.

Phew. Again, I have not verified any of the Windows behavior.

▶ Reply

Permalink Reply by Render Plus on June 7, 2011 at 11:53am

Thanks for chiming in here Roy. I was hoping you knew more about hyperthreading than I did.

IRender nXt has a setting on the More tab to use:

1. All reported threads,

2. All but one (the idea was to leave a thread for other tasks. nXt sets it thread use to low priority, but some users feel that the rendering still uses too much of their processing power. This setting may help with that.)

3. A fixed number - you can set this to less that the number of threads reported by the OS, or to more.

I need to do some testing to wee what kind of rendering times vs other App performance you get with various settings.

▶ Reply

Permalink Reply by Roy Hirshkowitz on June 7, 2011 at 11:58am

Keep in mind that these can only set a limitation on the number of threads to create. The absolute max is always the # of reported cores (as detailed above) x 2.

▶ Reply

Permalink Reply by Render Plus on June 7, 2011 at 12:07pm

Oh - I didn't know that. I will send you the routine I use to get the "reported cores" to make sure I am getting it properly.

▶ Reply

Permalink Reply by Paul Davis on June 7, 2011 at 3:11pm

I went from an i5 to an i7 and had them both clocked at 4.0ghz. The i7 definately performed better (15-20%range). I'm running windows 7 64 bit with my latest version of nxt that dates back to january. My desktop gadget shows all 8 cores (4 of them virtual) at %100 usage.

In my opinion the best answer would be get an i7 if you can get it for a good price. I got my i7 940 with motherboard on craigslist for $300.00. that was cheaper than I could get a new i5 with motherboard for. also, clockspeed is going to be a bigger difference. So either overclock it or by a higher end i5 with a fast speed (3.20 or better).

Either way the intel "i" series processors are going to greatly increase rendering time compared to the older core 2 duos or quads.