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When does cpu-gpu bottleneck occurs? e2200+SLI / e6600+HD4870 exemple

Last response: in CPUs
October 12, 2009 12:20:09 AM

Bottleneck: A phenomenon where the capacity of an entire system is limited by lowest-capacity part of such system

I heard my intel e6600 could overclock easily to 4GHz on air, so I went on and bought a good cooler. After many attempts and reads, I concluded that unfortunately my old motherboard isn’t a good overclocker. So again I went on and found a new motherboard and successfully got it stable at 3.6 GHz without compromising it with too high voltage. I found out my old board max possible fsb was around 1200(300*4). Figured out I’ll buy a processor with lower fsb than the e6600 to fit in, ended up with intel e2200, been able to overclock it to 3.3GHz stable.

1st computer specifications:
CPU: Intel e2200 OC'd @ 3.3ghz (300x11 with 1.3v) **stable with dual Prime95 for 4hours**
GPU: 2x BFG NVIDIA GeForce 8800 GTS OC 320MB PCIe **SLI**
Board: Asus P5N32-SLI SE Deluxe **NB: nForce4 SLI Intel / SB: nForce4 MCP**
RAM: Mushkin EM2-6400 2x1GB **DDR2 800mhz, CAS 5-5-5-12 @ 1.8v**
HDD: 2x Seagate Barracuda 7200.11 SATA 3.0 GB/s 320GB **onboard Raid-0**
PSU: Ultra X-Finity™ 600 Watt SLI-Ready **4 years old**
Case: CoolerMaster Centurion 590 **5x120mm Fans: 1 front, 2 top, 1 back and 1 side**
Heatsink: Scythe Mugen 2 **extra 120mm fan**

2nd computer specifications:
CPU: Intel e6600 OC'd @ 3.6ghz (400x9 with 1.3v) **stable with dual Prime95 for 4hours**
GPU: ATI Radeon HD 4870
Board: Gigabyte GA-EP45-UD3R **NB: Intel P45 / SB: ICH10R**
RAM: OCZ Gold PC-6400 2x2GB **DDR2 800mhz, CAS 5-5-5-18 @ 1.8v**
HDD: 2x Western Digital Caviar Black SATA 3.0Gb/s 5000GB **onboard Raid-0**
PSU: OCZ ModXStream Pro 700watt **New**
Case: CoolerMaster Centurion 590 **5x120mm Fans: 1 front, 2 top, 1 back and 1 side**
Heatsink: Scythe Mugen 2 **extra 120mm fan**

While messing around I noticed the e2200 overclocked is not as fast as the e6600 at stock speed in different games with the same rig. During the process I ended up with a question about bottleneck: how does it work exactly? What causes a bottleneck? I have been surfing around to understand properly bottlenecking but only found comparison between different cpu/gpu, no real what/why explanation. I was wondering is it just a matter of megahertz? What specs of the cpu or gpu is important to look for? Is the ram or motherboard involved?

So I ended up pairing my e6600 with a HD 4870. It is working flawlessly but I am wondering if am I also bottlenecking my video card without even knowing it? Does today’s high-end video card really need high-end processor also? It would be interesting to be able to calculate when would bottleneck occur for any piece of cpu or gpu. If anyone could enlighten us on this would be very great. For general knowledge, can cpu/ram bottleneck occur?

Here’s maybe some things to start with:
CPU (socket, core speed, bus speed, bus/core ratio, number of cores…);
GPU (core speed, shaders speed, memory speed, memory bus width etc...);
RAM (frequency, latency…);
Board (Northbridge or Southbridge specifications).

Hope this will be informative for everyone. Thanks for reading and answering.
a b à CPUs
October 12, 2009 1:54:23 AM

Duplicate of following post.
a b à CPUs
October 12, 2009 1:57:21 AM

benoitd said:

is it just a matter of megahertz? What specs of the cpu or gpu is important to look for? Is the ram or motherboard involved?

It would be interesting to be able to calculate when would bottleneck occur for any piece of cpu or gpu.

I wish it were so simple. Bottlenecks occur because of differences in the processing power of the various components. However that processing power is depend on the application(s) used - and there are a lot of inter-related intervening variables. Certain video applications are very CPU intensive while games are more video card intensive. Some applications make better use of multiple threads or cores - so they can make better use of multi-core processors but this then puts more "pressure" on the other components. Some applications can make better use of more memory than others. It you just look at the THG charts for CPUs and video cards you will see how different systems performance is ranks differently for the various applications or even just different games - depending on how the game code is written. And if you run multiple applications (or have other garbage running on your PC) that is another variable.

And no - it is not a simple matter of megahertz even just for one component such as CPU. There are differences between AMD and Intel and differences between models within each manufacturer. Generally each new processor architecture has improvements that make it substantially faster than the previous one for a given speed.

Look at the THG charts to compare individual components such as CPUs and video cards. Look at the test setups to get some idea of the rig used to ensure the other components will not bottleneck the component being tested. Look at test results for systems similar to yours. Get benchmarking software to test your own system and then make changes (perhaps with borrowed video cards) to see if there is a performance difference.

Beyond that, identify your applications and a model system and ask experts if they can suggest tweaks to improve performance for the specificed applications.
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a b à CPUs
October 12, 2009 2:16:54 AM

If you keep your cpu and gpu within 2 years of each other you won't have huge issues with bottlenecking.

Anything above that and you will start to see it occuring. I have a Q6600 overclocked to 3.25ghz and it clearly bottlenecks my 5850 whereas my 940 BE overclocked to 3.6ghz doesn't. The Q6600 was a great match for my old 8800gt, and was still pretty good with my 4870, but it cannot handle the power of a 5850. Don't think I mean it can't run the games, of course it can - but it's just not at the same level as the phenom II. When your processor is costing you 10-15 fps, thats when it's time to consider an upgrade.
October 12, 2009 12:55:37 PM

thx for answering hope it goes even more technical

rockyjohn: Ok, i get it, bottleneck occurs when the application(s) used put more pressure on the cheapest part of your computer, but there must be numbers that can back this up...when would it happens?

jennyh: two years old...the e6600 is more than 2 years older than the ati radeon hd 4870. It works well, but could i get more from my 4870?
a b à CPUs
October 12, 2009 2:31:54 PM

When would it happen? Most likely always. For any given application, you are almost always going to have a bottleneck - because it will process the data as quickly as it can - limited by the slowest component relative to that application. With simple applications, the data is processed so quickly you don't notice - but some component is still limiting how quickly the processing is done. With games, same thing. The better the system the faster the game. Above a certain thresshold you won't notice the improvement in Fps - but there is still a bottleneck keeping system from processing faster.

"but there must be numbers that can back this up" - Why?
Again - there are many variables - all of the different components, normal variiations in the manufacture of products (for instance one stick of memory may work in a system when another of the same model will not - or some specific CPUs may OC better than others of the same model - just variation in production), and all the different applications many with numberous subroutines. The number of combinations must be in the millions - with any specific "numbers" only applying to the one specific case.