The chip at the heart of the original Raspberry Pi (a Broadcom BCM2835 processor) was originally designed to be a Graphical Processing Unit (GPU) for mobile and embedded applications. The ARM core that drives most of Raspberry Pi's functionality was added because some extra space was available on the chip; this enabled this powerful GPU to be used as a System-on-Chip (SoC) solution.
An SoC is an integrated service microchip with all the necessary electronic circuits and parts of a computer or electronic system, it is used in smartphones or wearable computers, on a single integrated circuit (IC).
As you can imagine, if that original ARM core (ARM1176JZF-S, which is the ARMv6 architecture) consisted of only a small part of the chip on Raspberry Pi, you would be right in thinking that the GPU must perform rather well.
