Intel Clarkdale vs AMD Phenom II with 785G – Mainstream Showdown

CPU by massman @ 2010-01-11

With the launch of Clarkdale by Intel, they have finally released a Nehalem for the masses, the Core i3 and i5 variations with integrated graphics are a direct competitor to the market segment currently held by AMD Phenom and Athlon CPUs. In this article we compare the performance of the IGP on the Intel Core i5 661 to and AMD system with 785G chipset.

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Introduction : "Who cares about NDA?"

Less and less people, apparently. Although it's not our intention to make a big deal of this, again, we do wonder why we bother to stick to the NDA set by Intel when we could just buy the technology months in advance. Well, this article is exactly what we plan to do about it: instead of releasing a finished article the minute the NDA is over, we wait a couple of days. Yes, that's how we roll!

The advantage of this action is that we don't have to bother running all the uninteresting tests and focus on what interests us. Instead of the normal series of benchmarks, comparing the newly released technology against the existing technology and come to the conclusion that it's pretty decent stuff, we will be looking at how useful this Clarkdale is in comparison to the already existing Phenom II ... IGP solution! Will Intel crush its mainstream rival ?

Madshrimps (c)

As you probably already know, the Clarkdale differs from any other Intel technology released so far by the integration of a graphics processor on the CPU die. As the picture above shows, it's not integrated into the CPU itself, but it's located in the package.

The interesting part is that this redefines the concept of integrated graphics completely. Whereas this used to be a graphics core integrated either separately or into the Northbridge, it is now located under the same hood as the processor. This means: one chip less that draws power and generates heat, only one cooler needed to cool down the system and the possibility to make smaller PCBs housing the entire tech you needed.

The Clarkdale IGP

Again, I have to, no: want to, refer to other articles around the web if you want to know the exact specifics of the technology behind the integration of the graphics processor. In my humble opinion, there are only TWO important notes to make:
  1. The graphics core is build using 45nm transistor technology, ergo the biggest die on the cpu package
  2. The memory controller is located on the die of the graphics processor

In fact, only the latter is really interesting to ponder about. Let's go back to the design of the latest IGP technology: AMD's 785G housing the HD4200 (which is actually just the HD3300 with added DX10 feats, but that's not the topic of today). The graphics processor is located in the NB, which is connected to the CPU by the infamous HT Link. Now, any graphics core needs some sort of cache or memory to store data, so AMD developed two solutions: UMA and sideport. The UMA technology reserves a part of the system memory to store vga data, sideport memory is a dedicated memory chip located nearby the Northbridge also serving as storage for vga data. Now, there are two reasons why the sideport memory has been added to high-end IGP mainboards:
  1. Faster acces
  2. Power saving purposes

Both reasons are actually part of the underlying issue of using system memory to store vga data. When the IGP is in load mode, loading and storing data in the system memory takes up too much time to deliver decent performance. As the memory controller in the Phenom II is also located on the cpu die, the following path has to be followed from the IGP to the system memory:

IGP --> NB --> CPU --> IMC --> DRAM

And of course all the way back again. Having a dedicated amount of memory on the side, the sideport, reduces these latencies. An optimisation, yes, but sadly enough this solution also has its limitations as the maximum amount of sideport memory is a mere 128MB, a lot less than what current games require. In other words, although the problem is partially solved, using sideport memory only will not be a viable solution if you want to play some games at higher resolutions and quality settings.

Here's where the Intel engineers come in. Since the graphics processor is already integrated on the cpu die, the biggest latency bottleneck of the Northbridge is already removed. The brilliance of the design is that the memory controller has been integrated on the IGP die ... as close as possible to the GPU! No need for sideport memory ... another cost avoided!

(oh by the way, I've just hinted you on how you increase the performance of your HD4200 by overclocking: increasing the clock frequency of the HT Link and the NB will significantly increase the frames per second due to a faster transfer rate of vga data)
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Comment from jmke @ 2010/01/11
Comment from wutske @ 2010/01/11
Too bad the memory timings of both systems weren't the same because this biasses the results (as you've mentioned in the review).
Comment from jmke @ 2010/01/11
yes and no.
the memory subsystem for Clarkdale is noticeably lower due to its design, but even then the CPU is never bandwidth starved, even with the slowest of DDR3 sticks.
Comment from wutske @ 2010/01/11
okay, but now it's not only the CPU which needs the memory but also the GPU.
And some synthetic benchmark do benefit from the lower latencies (like on the AMD setup).
Comment from Massman @ 2010/01/11
There are still issues with the current H55 mainboards in terms of delivering decent memory performance. Either the Clarkdale is just no good for high memory bandwidth, or the bioses are too immature.