CPU vs GPU Rendering: Differences, Advantages, and Use Cases

When rendering with a computer, there are two popular systems: CPU‑based and GPU‑based.

CPU rendering uses the computer's central processor to execute scenes and produce near‑perfect results, representing the traditional approach. GPU rendering, which leverages graphics processors, has become popular because GPUs can provide comparable results in many cases.

In general, GPU rendering runs many parallel processes, making it faster but limited in the types of tasks it can perform, so it may struggle with large, detailed scenes. CPU rendering runs fewer parallel processes but can handle a wider variety of tasks, delivering more detail; a Mythbusters demo illustrates the difference.

In this article we study CPU and GPU rendering, point out their differences, and consider which is best suited for various goals and constraints.

What is rendering?

Rendering is the process of generating a final image from a 2D or 3D model using computer applications, adding textures, lighting, and camera angles until the output is complete.

Rendering in a computer system is performed by either the CPU or the GPU, and sometimes both in hybrid setups such as V‑Ray.

CPU Rendering: Basics

CPU rendering engines provide many features to fine‑tune scene parameters. Modern CPUs have many high‑frequency cores; more cores improve rendering performance. High‑end CPUs can have up to 64 cores and access system RAM, allowing large data sets. Pixar uses CPU rendering for high visual quality.

CPU rendering excels in architectural design and complex geometry where detail matters.

GPU Rendering: Basics

GPU rendering makes high‑performance rendering more affordable. GPUs have thousands of low‑clock cores that run tasks in parallel, giving them a speed advantage, especially for real‑time graphics in games. GPUs also drive advances in AI, big data, and cryptography.

GPU rendering is becoming more common, challenging traditional CPU systems; Autodesk’s Arnold now offers a GPU engine.

CPU vs GPU: Differences

GPU (right) shows lines that CPU (left) does not.

Design

Threadripper 3990X has nearly 64 cores; GPUs like the RTX 3090 have 10,496 cores but lower clock speeds. Core count and clock speed affect performance differently.

Quality

CPU cores are fewer but more versatile, handling complex instruction sets and delivering higher quality with less noise. GPU renders often exhibit more noise.

Memory Advantage

High‑end motherboards can hold up to 128 GB RAM; CPUs can access system memory, with Threadripper supporting up to 512 GB DDR4. GPUs are limited by VRAM (e.g., RTX 3090 has 24 GB).

Complex Scenes

CPU can handle varied tasks, useful for heterogeneous workloads. GPU is limited by hardware design, VRAM, and slower cores, making it less suitable for highly complex scenes.

Stability

CPU is well‑integrated with operating systems and has mature drivers, resulting in higher stability. GPUs can be prone to failures due to power spikes, driver updates, or compatibility issues.

Speed

GPU parallelism usually yields faster render times, especially for real‑time applications. CPU cores run sequentially and are generally slower, with limited resources for rendering.

Regular Improvements

GPU innovation cycles are faster than CPU, with companies like AMD and Nvidia pushing performance each generation. CPUs are approaching Moore's Law limits, slowing performance gains.

Hardware Cost

High‑end GPUs (e.g., RTX 3090) cost around $1,500, while powerful CPUs like Threadripper 3990X cost about $5,000. GPUs are easier to upgrade by adding another card, whereas CPU upgrades may require additional compatible hardware.

Render Engines

Render engines determine whether CPU or GPU rendering is used. CPU‑focused engines include Arnold, Corona, and 3Delight; GPU‑optimized engines include Blender Cycles, Octane, and Redshift.

Rendering Hardware

Balanced hardware settings are crucial for optimal performance; benchmarks like Cinebench (CPU) and OctaneBench (GPU) help evaluate capabilities.

Conclusion

Pixar’s film "Up" used CPU rendering. In summary, if your workflow prioritizes speed, lower complexity, and cost, GPU rendering is advantageous; if you prioritize quality, can afford higher hardware costs, and need to handle complex scenes, CPU rendering is preferable.