Intel unveils Larrabee details

Posted at: 10:28am 4th August 2008 by Ben Hardwidge

The most fascinating graphics product since the original 3D accelerators

You can now stop counting down the days to Siggraph on your calendar, as Intel has finally unveiled the truth about its Larrabee graphics architecture, and it’s completely different from any GPU we’ve ever seen.

The first feature worthy of note is that Larrabee is indeed based on several original Pentium cores, as we reported last month. Of course, the Pentium cores have had a bit of souping up since last decade, and Larrabee’s cores will also feature a 16-wide vector unit, 64-bit extensions, a sophisticated prefetching system and the ability to execute four threads.

Each core will not only feature a wide vector unit, but it will also feature a scalar processing unit. As well as this, each core will have access to a huge pool of Level 2 cache, and the chip will feature a ring bus memory system, much like ATI’s GPUs.

Hardware intricacies aside, though, the major shocker with Larrabee is its graphics pipeline. Those of you who are old enough to remember playing first person shooters before the first 3D accelerators turned up may rightly start backing into a corner at the mention of ‘software rendering,’ but this is precisely what Intel has planned for Larrabee.

The advantage of this, according to Intel, is that every stage of the pipeline is completely programmable. Currently, only the geometry shading, pixel shading and vertex shading stages are programmable on a current GPU architecture, but Larrabee’s software-orientated architecture will mean that the rasterisation, primitive setup and frame buffer blend stages are also fully programmable.

This means that Larrabee will not only be completely compatible with DirectX and OpenGL, but that it can also be easily opened up to other new APIs with its x86-based architecture. On top of this, it could also theoretically work with future versions of DirectX via a software update, without having to upgrade your hardware. However, Intel has also added a few fixed function blocks to the Larrabee architecture for features such as texture filtering.

Intel has also outlined a few of Larrabee’s potential 3D visual benefits, which include an ‘irregular Z-buffer’ that results in clean, non-jagged edges of shadows. Intel also claims that Larrabee’s ability to process multiple layers could result in more accurate transparency effects, and provided the example of seeing post-processing effects, such as fog, through transparent surface such as a dragon’s wing.

One feature Larrabee does have in common with current GPUs, however, is the ability to scale well as more cores are added. According to Intel’s own test results, F.E.A.R., Gears of War and Half-Life 2: Episode 2 all pretty much doubled their frame rate as the number of cores doubled, up to a total of 64 cores. Intel hasn’t confirmed how many cores Larrabee will feature, or whether dual-graphics card configurations will be available to take further advantage of this. However, we asked Intel’s Nick Knupffer about the ability to chain together Larrabee cards, and he told Custom PC that ‘you should expect the sort of features that are in high-end GPUs will still be the kinds of features that Larrabee will support.’ Basically, it’s not a confirmation, but it looks likely.