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How to calculate if you have a bottleneck in your new build?

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December 7, 2010 5:34:51 PM

I read about a lot of technology and brands lately.
Slowly I begin to understand what is the difference between DDR 2 and 3 :) 

I got a question:

How do you see and calculate where and when you have a bottleneck in your system?
Like would i7 950 with 2x 6850 and 4 GB ram make a bottleneck somewhere?
What speed my hard disk must be to keep up? And why people recommend small SSD's for system?

Help would be greatly appreciated.
Thanks
a b B Homebuilt system
December 7, 2010 6:09:04 PM

Bottlenecks are hard to test, outside swapping parts and seeing what happens. This is because the bottleneck will vary from game to game.

In general, GPU is usually the bottleneck if you want to play with eye candy and 1080p, at least until you get past the 100FPS or so range. One notable exception is Civ 5, but that game has major issues.


You can just read reviews of the 6850 xfire to see where the bottleneck lies in individual games.
http://www.anandtech.com/show/3987/amds-radeon-6870-685...

HD speed relates to load times, not FPS. SSD are recommended for boot drives due their massive increases in load times, boot times and response times over traditional HD's.

There are some software programs that are billed to help you determine, such as Passmark. However, they're synthetics and like all synthetics, are of minimal real world value.


December 7, 2010 6:48:41 PM

Too little RAM is probably the easiest bottleneck to spot, because you can monitor memory consumption and if all physical is gone (excepting caching etc) then that's one bottleneck in the system. Actually you could do the same for CPU - if none of your cores are nowhere near 100% utilization that can't be the bottleneck...

By logic of elimination, I suppose you could arrive at the conclusion that it must be the GPU. But then again you could have multiple bottlenecks (such as an old HDD being a bottleneck whenever/if the game needs to load a bit more data from the disk).

I think it's not a calculation, but a seat-of-the-pants judgement when you talk system design. Look at hierarchy/tier charts from Tom's. What other people put in their systems or recommend. Benchmarks that compare different GPUs, CPUs, RAM technologies... You get a general picture of what goes nicely with what. Just take into account that system builders will figure in their upgrade paths - eg. go with a lower power GPU because you can upgrade that later, while keeping the existing CPU.

But every game is different, sometimes rather significantly so. For example I play a fair deal of overhead RTS - Eve Online is a nice example, where you can zoom way out and all you see might be red and green dots, not 3d models with gazillion polygons. Those depend more on CPU... which gives me a bit of second thoughts about having chosen a core i3 for mine :sarcastic:  If I load up a FPS like say Bad Company 2, the bottlenecks move to different places.

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December 7, 2010 6:48:53 PM

So if say I take an i7 950 cpu and 6850 xfire which kind of ram would be the most beneficial? 1600? 2000?
December 7, 2010 6:53:32 PM

Forgot to add that you might do something else than gaming with your puter, even so much that performance in that activity is really important. CPU and disk speeds may become more important. For example if you do raytracing, CPU power (and quite possibly the number of cores) is paramount. If you do serious web browsing with dozens of tabs, your system will easily consume 2+ GB of RAM. And so on. So it's really a rather complex decision. You have to balance between different usage scenarios.
December 7, 2010 7:24:06 PM

I really would like to understand the RAM type impact, not only the amount of RAM in the system.. Thanks :) 
a b B Homebuilt system
December 7, 2010 7:34:21 PM

My standard block of text.

AMD architecture favors tighter timings over faster speed for
performance increase. Intel, favors neither. That said, neither makes
a significant impact on performance to warrant a major price
difference.

CAs latency refers to how long it takes the RAM to do something after
it's given a command. Makes no difference to FPS in gaming, but like
an SSD, it improves system responsiveness.

Stock i7-930 is 133 block, 21 multiplier and 10x memory multiplier.
Though the latter is determined by MOBO not CPU. This fully saturated
1333mhz RAM. 133block speed x 10 memory multiplier= 1330.

To OC above this you'll need to either lower multiplier or get faster RAM.
In general, we recommend DDR3 1600 RAM if you plan on a OC.

Now, the reason why we recommend G Skill RAM is that memory can
perform better than rated speeds. Most companies sell you RAM that'll
perform at specs, G SKill tends to give you better than you pay for.
So their RAM can run at higher speeds, lower voltages and/or lower
timings than specs. OCZ is the opposite, hence we don't recommend
them.

High speeds requires looser timings to work. I'll avoid the
tech details as to why, but suffice to say this is a mechanically
imposed limitation. Now, because faster RAM must be of higher quality
to maintain the same latency as slower RAM, they're generally better
quality. As a result, the Trident DDR3 2000 kit that's rated at cas 9
at 2000, can hit CAS 6 at 1600 speeds. CAS 5 at 1333 speeds. This is
why people will buy extremely fast RAM. They're getting higher quality
RAM so they can run it at tighter timings for the speeds they want.

Now as to why 1600 7-8-7-24 kit is better than a 1333 7-7-7-21 kit, is
because, the 1600 kit can run 7-7-7-21 when under clocked to 1333
speeds.

TLDR You get faster RAM because it'll get better timings when you
underclock it to speeds you're using, or you plan on OCing.

RAM amount is simple. You need enough for the game and background processes to run. Anymore is of no impact in XP. In win 7 superfetch does benefit from excess RAM, but that has no affect on gaming FPS.
December 7, 2010 7:56:54 PM

Very good reply, now I really understand what I should do with fast RAM if I decide to buy it :) 

Thanks
!