Quake 3 running on the Raspberry Pi. Though, the graphics might not be all that demanding by today's standards.
Raspberry Pi's executive director Eben Upton stated, during a Game Industries interview, that the company's platform will be able to outdo the iPhone 4s graphically "across a range of content." Helping the Raspberry Pi's ARM 11 component of this system on a chip (SoC) is a Broadcom BCM2835 Dual Core "VideoCore IV" multimedia co-processor . The GPU portion is capable of 1 Gigapixel per second fill rate.
Upton continued, "To summarize, BCM2835 has a tile mode architecture - so it kills immediate-mode devices like Tegra on fill-rate - and we've chosen to configure it with a very large amount of shader performance, so it does very well on compute-intensive benchmarks, and should double iPhone 4S performance across a range of content."
As a side note, Upton said that the Raspberry Pi can be overclocked, but only by 100 Mhz at the utmost. He explained, "The ARM is already fairly close to the edge at 700 MHz. Without overvolting the chip (which decreases lifetime), there's not much more than 100 MHz of overclocking headroom on typical silicon. We do offer a clock speed tweak option in the boot configuration parameters, so if you get lucky and get a fast part you can exploit it."
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