The north bridge and IGP

Although Clarkdale’s north bridge and integrated graphics processor only incorporates 177 million transistors, it is a larger chip at 114 mm², in part because it’s produced on a 45-nm fab process. This chip sports 16 lanes of PCIe Gen2 connectivity and a dual-channel memory controller capable of supporting DDR3 at up to 1333 MT/s.

The single largest component onboard, though, is the integrated graphics processor. The fact that Intel has integrated graphics into the same package as a 32-nm microprocessor makes us somewhat ambivalent. The company seems to have taken its best technology and arguably its worst technology and made us a sandwich—peanut butter and Vegemite, if you will. We can’t entirely overlook the fact that a firm with a near monopoly in the CPU market has decided to integrate a graphics solution directly into its core products, either. Third-party GPU suppliers like Nvidia can’t be pleased with this development. With that said, when I asked him about this move this past summer, Nvidia’s David Kirk argued persuasively that his company wouldn’t lose any business that it wouldn’t have lost to the IGP in Intel’s chipsets in the past.

For its part, Intel says it has focused on providing an improved user experience for today’s usage models, particularly in Windows 7, with Clarkdale’s IGP. (By the way, as far as I can tell, the IGP’s only name is the very generic Intel HD Graphics.) Although it’s not a world-beater, the IGP’s 3D graphics core has been enhanced in numerous ways. The number of execution units has risen to 12, versus 10 in the G4x-series chipsets. Those execution units are essentially unified shaders compatible with DirectX 10’s Shader Model 4.0 and with OpenGL 2.1. (The G4x supported DX10, but only OpenGL 2.0.)

In answer to our questions about the relatively weak performance of past Intel IGPs, some seemingly basic features are new to Clarkdale’s IGP. The vertex processing hardware now supports cull, clip, and setup, for instance. Intel has also added a fast Z clear function and hierarchical Z support. Both should improve the IGP’s efficiency and performance, but these are features Nvidia and ATI were busy adding to their hardware way back in the DirectX 8 generation. Seriously. Being able to discard the contents of a depth buffer and start over is a pretty old trick, as is the quick rejection of occluded objects. Better late than never, though!

The IGP’s display pipelines and video processing unit have both been substantially upgraded, as well, with near-best-in-class capabilities. The hardware supports dual displays, each at resolutions up to 2560×1600, and it can now drive two displays simultaneously over HDMI, which the GMA 4500 series couldn’t do. Richer colors are on the menu thanks to support for 12-bit-per-channel Deep Color over DisplayPort and HDMI, along with xvYCC capability for an expanded color gamut with wide-gamut displays.

Intel looks to have focused quite a bit on home theater PC-type usage models, and since display standards now carry audio signals, Clarkdale’s IGP incorporates robust support for sound, as well. The IGP can stream up to eight channels of LPCM audio at 24 bits and 96 KHz. Supported standards include the lossless Dolby TrueHD and DTA-HD Master Audio codecs, both of which are used by Blu-ray titles.

Speaking of Blu-ray, the IGP’s video unit provides “full” hardware acceleration for the decoding of the most popular video compression standards: H.264/AVC, VC-1, and MPEG2. This unit can now decode dual video streams simultaneously, helpful for Blu-ray discs that include features like picture-in-picture director’s commentary. To make sure those abilities don’t go unused, Intel has worked with third-party vendors to include support for its acceleration hardware in popular applications like ArcSoft Total Media Theater, CyberLink PowerDVD, and Corel WinDVD.

Core i3-500 and i5-600 series pricing
Now that we’ve properly introduced the technology, let’s take a look at the seven different Clarkdale variants Intel is introducing today for desktop PCs. The pricing and basic feature sets are listed below.

Model Cores Threads Base core
clock speed
Peak Turbo
clock speed
L3 cache
TDP Price
Pentium G6950 2 2 2.8 GHz 3MB 533 MHz 73W $87
Core i3-530 2 4 2.93 GHz 4MB 733 MHz 73W $113
Core i3-540 2 4 3.06 GHz 4MB 733 MHz 73W $133
Core i5-650 2 4 3.20 GHz 3.46 GHz 4MB 733 MHz 73W $176
Core i5-660 2 4 3.33 GHz 3.60 GHz 4MB 733 MHz 73W $196
Core i5-661 2 4 3.33 GHz 3.60 GHz 4MB 900 MHz 87W $196
Core i5-670 2 4 3.46 GHz 3.73 GHz 4MB 733 MHz 73W $284

That’s a pretty broad range, and at the high end, it overlaps in interesting ways with the Lynnfield-based Core i5-700 series. Take, for instance, the Core i5-661 processor Intel supplied us for review. Thanks to Hyper-Threading, the i5-661 shows four threads in Task Manager, and thanks to Turbo Boost, its clock speeds range up to 3.6GHz—as high as the peak frequency for the much more expensive Core i7-870. The Core i5-750 is priced the same as the i5-661, also exposes four threads, and has a Turbo Boost peak of 3.2GHz. So, much like the Core 2 lineup, the Core i5 series presents you with a trade-off: you may have two faster cores or four slower ones for the same price.

Please do note that the Core i5-661 has a 900MHz IGP frequency and an 87W TDP rating, while the rest of the Clarkdale Core i3/i5 models have a 733MHz IGP and a 73W TDP. Also note that the Core i5-661 is the only Clarkdale processor we received for review ahead of this product launch. One Intel representative we spoke with called the i5-661 “a niche product” intended for premium home theater PCs. In other words, the vast majority of Clarkdale systems will likely have a 733MHz IGP clock, instead, and results from the 900MHz IGP on the Core i5-661 are not likely to reflect their graphics performance. We did request other Core i3/i5 models for review, but Intel declined, leaving us with only this self-described “niche product” to test.

Happily, the BIOS on our Asus H57 motherboard gives us easy control over the IGP clock, so we lowered it to 733MHz and ran a set of rests simulating the performance of the Core i5-660’s IGP. Sadly, we were not able to adjust the IGP voltage, so we couldn’t confidently simulate the power consumption of a 73W Clarkdale product.

Clarkdale chip… sets?
The final piece of the Clarkdale puzzle is a trio of new supporting chips, the H55, H57, and Q57. I believe they’re all just different spins on the same silicon. In fact, I believe they may be based on the same 65nm silicon as the Lynnfield processors’ P55 PCH. This I/O chip augments the Clarkdale package with a range of I/O interfaces for things like SATA and USB.

Block diagram of an Intel H55-based system. Source: Intel.

The most notable new addition in the Clarkdale-focused versions of this chip is support for the Intel Flexible Display Interface (FDI), needed to pipe the IGP’s graphics out to a display. The FDI interconnect is based on DisplayPort. The H55/H57/Q57 have two independent FDI links, one for each display supported, and each one has a 2.7Gbps data rate.

Beyond that, much in these chips will be familiar. The DMI interface handles all other communication between the Clarkdale package and the chipset, with aggregate data rates of up to 1 GB/s in each direction over its four pairs of unidirectional links. The PCIe x1 links on this chip remain Gen2-compliant but with only Gen1 data rates.

In fact, the differences between the chipset models is largely just positioning. The H57 includes Intel’s Rapid Storage Technology, evidently the new name for the former Matrix Storage Technology, which includes RAID capability. The H55 lacks this feature, and it has two fewer USB and PCIe x1 ports, although its 12 USB ports and six PCIe ports should suffice in most cases. And the Q57 is simply the commercial version of the H57, intended for corporate desktops. For the record, Intel says the Q57 costs $44, the H57 $43, the H55 $40, and the P55 $40.

We have two examples of motherboards based on these chipsets in house for testing. The first one to arrive was the Intel DH55TC, a microATX board with a pretty standard array of ports and slots.

Unfortunately, our particular copy of this board had some stability issues, which we suspected might have been caused by a memory problem. We tried several different sets of DIMMs, to no avail, and since this board’s BIOS offers zero control over memory voltages and timings, we were helpless to move ahead.

Instead, we dialed up Asus and got them to send out an H57 board, the P7H57D-V EVO. True to Asus form, this board has a full suite of BIOS-level controls over all sorts of variables, along with a robust set of features that includes USB 3.0 and SATA 6Gbps. Best of all, our stability problems were instantly resolved.

In a funny twist, this board has a pair of PCIe x16 slots with support for both SLI and CrossFire. If a single GPU is installed, the board directs all 16 PCIe lanes to slot one. If a second card is installed in slot two, it splits the PCIe lanes into a dual x8 config. That happens in spite of the fact that the Intel specifications say such a bifurcation of the CPU’s PCIe lanes is only supported when the P55 chipset is present. Looks like Asus is bringing outlaw goodness to the masses. We’ll hopefully be able to bring you a full review of this board after CES.


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