Intel i7-3770K Ivy Bridge CPU Review

Author: MAC
Date: April 23, 2012
Product Name: i7-3770K
Warranty: 3 Years
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An In-Depth Look at Intel's HD Graphics 2500 & 4000 IGPs

While we were genuinely impressed with the progress Intel made with Sandy Bridge’s IGP, six months later it got blown out of the water in grandiose fashion by the significantly more powerful Radeon HD 6550D found in AMD’s Llano A-series APUs.

With Ivy Bridge, Intel is trying to regain some of that lost ground, and they are touting the HD Graphics 4000 as being capable of a twofold increase in GPU performance over the previous HD Graphics 3000. They have accomplished this in a number of different ways but as before, their processor graphics is still broken into two categories called GT1 (HD2500) and GT2 (HD4000). GT1 is once again geared towards the lower end of the spectrum while GT2 will typically be attached to higher level solutions.

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When compared to the units contained within Sandy Bridge processors there have been plenty of architectural changes to Intel’s integrated graphics cores this time around. The Processor Graphics Unit is now broken up into three distinct graphics processing stages: the Global Assets containing the fixed function stages along with the Geometry engines, the Slice Common with its Rasterizer, L3 cache setup and pixel back ends and finally the main Slice unit which houses the Execution Units, L1 cache and other rendering pipeline necessities. Separate units have also been included for the Media CODECs and necessary display output features.

As with Sandy Bridge’s architecture, the Execution Units still do the lion’s share of heavy lifting in this core design. Much like NVIDIA’s cores or AMD’s shaders, they are responsible for the day to day multistage processing for both graphics and compute workloads. However, Intel has now added support for Compute Shaders so high levels of parallelism are now possible and shared local memory has been added to increase the performance of Direct Compute applications. As necessitated by the addition of DX11, the architecture also supports Shader Model 5.0.

Speaking of the switch to DX11 compatibility, it has necessitated the modification of the primary rendering stages. A dedicated tessellation unit as well as a pair of programmable stages –the Hull Shader and Domain Shader- has been thrown into the equation. In order to further aid DX11 performance, the architecture now supports BC6H/7 compressed texture formats as well.

While Intel have made plenty of sizeable microarchitectural enhancements to the graphics processor, what’s really interesting is that they have given the IGP its own L3 cache. While the Last Level Cache (LLC) is still shared between CPU and IGP, this small cache has been integrated into the graphics core and slightly reduces the need for the IGP to use power-hungry 256-bit ring bus interface that connects all the elements of the chip. This change, along with the lower GPU frequency and voltage, and of course the switch to the 22nm process has allowed Intel to double GPU’s performance per watt.

Along with the architectural improvements that may not be apparent by looking at the on-paper specifications of Ivy Bridge’s Processor Graphics, the HD4000 series now includes 16 Execution Units, an improvement over the 12 within Sandy Bridge’s higher end layout, resulting in a twofold improvement in certain cases. The HD2500 maintains the six EUs of the previous generation but with the wide range of on-die changes it should still offer a performance bump of between 10-20% in certain graphics intensive workloads. Quick Sync video transcoding and other GPGPU intensive tasks will also see a significant across the board improvement with these new PGUs, regardless of the clock speed differences.

The new HD graphics architecture isn’t completely focused upon offering a preset specification layout either. It is able to easily scale upwards or downwards, creating a nearly infinite list of derivatives. We likely won’t see any of these offshoots in this generation but expect higher performance from an expanded layout when Haswell hits sometime in 2013.

The HD Graphics on Ivy Bridge can dynamically adjust its frequency in order to automatically increase the clock speeds of the graphics controller when higher loads are detected. Much like the Turbo Boost technology on the CPU itself, this acts as a way to conserve power when high speeds aren’t needed and yet allows for on-the-call performance in demanding situations. And as you will see in our IGP gaming benchmarks section, the HD Graphics 4000 needs every bit of extra performance to compete with the Llano APUs.

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