Here's what that we know so far. The iPad uses Apple's own A4 chipset. At the heart of the chipset is the Arm Cortex (probably A8) processor running 1GHz. The GPU (the processor that handles all graphics, both 2D and 3D) is a variant of the PowerVR SGX design. This makes the iPad broadly similar to the iPhone 3GS. The 3GS uses the same CPU but clocked at 600MHz and is assisted by the PowerVR SGX 535.
If you've had the opportunity to play Gameloft's Brothers in Arms 2: Global Front on the iPhone 3GS you'll already know that in the right hands this Arm/PowerVR combination makes for some surprisingly rich visuals. Although the iPad's chipset does get a boast from the extra 400MHz of the CPU, without something a little extra in the GPU department game developers might struggle to match the frame rates that they regularly achieve on the iPhone 3GS. Why should be this be so?
There are three important specifications to keep in mind when considering 3D graphics hardware: Memory bandwidth, polygon rate and pixel fill rate. At 320 x 480 pixels, each fullscreen frame from a game such as the aforementioned Brothers in Arms 2 has a pixel count of 153,600 pixels. On the iPad with its 768 x 1024 resolution that figure jumps to 786,432, that's over five times the data being processed for each individual frame. Admittedly, we are oversimplifying things here, there are further factors that will present more challenges. The polygon count may be the same for both the iPhone and iPad variations of a game, but surely the developer will want to increase the texture resolution for the iPad version. Tiny textures originally designed to be viewed on a screen not much bigger than a business card, stretched out to roughly the size of paperback book are going to make for ugly looking games.
As we have already mentioned, Apple have confirmed that the iPad uses the PowerVR SGX graphics processor, what it hasn't confirmed for certain is which variant it has chosen to pack in the iPad.
This is important because the SGX535 is capable of pushing out 28 MPolys/s (million polygons per second) whereas the more powerful SGX545 ups that to 35 MPolys/s and with double the pixel fill rate of the 535. If the iPad is using the SGX545 it should give developers enough additional power to keep the frame rates up at 3GS levels whilst increasing the texture sizes significantly.
Even the SGX545 is not the end of the story. It's possible, though not probable, that the iPad's A4 chipset includes the PowerVR SGXMP (also known as the Series 5XT). This multicore graphics processor can reach PS2 levels of polygon performance at 133 MPoly/s in the four core version and a staggering 532 MPolys/s in the eight core design! That's right up there with the XBOX 360 and PS3. This is the very same GPU that is rumoured to be at the heart of Sony's PSP2.
As with the iPhone and iPod Touch, Apple have to find a perfect balance between battery life and performance. Based on the impressive battery life that Apple is advertising and some of the video demos of the very first iPad specific games, we believe that the iPad A4 chipset includes a faster version of the SGX535 (as including in the Phone 3GS) or possibly the SGX545.
April can't come soon enough!