GPU vs. CPU
A GPU is able to render images more quickly than a CPU because of its parallel processing architecture, which allows it to perform multiple calculations at the same time. A single CPU does not have this capability, although multicore processors can perform calculations in parallel by combining more than one CPU onto the same chip.
A CPU also has a higher clock speed, meaning it can perform an individual calculation faster than a GPU so it is often better equipped to handle basic computing tasks
In general, a GPU is designed for data-parallelism and applying the same operation to multiple data-items (SIMD). A CPU is designed for task-parallelism and doing different operations.