The GBA has a 32bit ARM7TDMI processor that runs on the RISC architecture. You can get all the documentation for the processor at
http://www.arm.com/. As far as we have been able to determine the processor is identical to the standard ARM7TDMI. It is a 16.78mhz system that has a graphics processor that accelerates many of the 2D tasks that free up the CPU to do some fairly impressive 2D stuff. This is not to say that the GBA is not capable of 3D effects (I will be very surprised if a Wolfenstein or doom port is not made within the year). In all the GBA is about equal in power to the snes maybe even a little better.
The GBA has a lot of ram available. It has 96KB of video memory, 32KB of fast internal ram and 256KB of external ram. The CPU is 32bit and can access internal ram 32bits at a time. External ram and ROM and video memory can only be accessed 16 bits at a time.
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