These days, a CPU constitutes multiple high-power cores that run an entire system. These cores run at a high frequency, enabling them to execute operations at a very fast rate. Additionally, the higher the number of cores, the better the rendering performance.

Modern day CPUs have up to 64 cores that allow for some excellent rendering performance. CPU rendering also benefits from the fact that it has access to onboard random-access memory (RAM). This allows the user to render scenes with huge amounts of data with relative ease. CPU rendering is also known for its quality of renders. For example, Pixar uses CPU rendering, hence the exceptional visual quality of its movies.

A good example of where CPU rendering would have an edge is architectural designs. If a scene is to be created with many complex geometries and tiny details, the benefits of CPU rendering would provide a much better and more accurate result.

A GPU has thousands of small cores that run at a relatively low clock speed. In this case, it’s the sheer number of these cores that allow the GPU to provide strong rendering performance. GPUs are inherently designed to run tasks in a parallel manner. This gives them an edge over CPUs, as rendering is a task that typically involves many elements. Because of this, GPUs are known for their extremely speedy rendering times.

Speedy rendering allows a GPU to process graphics in real time, and this is why you find that modern video games running much smoother with GPUs. Along with the gaming industry, GPUs have revolutionized the cryptomining, Big Data, AI, and machine learning fields.

GPU rendering is gradually becoming prevalent in many areas and is challenging traditional CPU rendering systems. Autodesk’s Arnold introduced their GPU render engine, recognizing the high potential.

While this overview of the differences can be helpful to get a clearer understanding of each system, there are a variety of unique features of CPU and GPU that are also good to know about.

Design

A powerful CPU such as the Threadripper 3990x has almost 64 cores (whereas an average PC has between 4 and 8 cores). These cores by number might be less when compared to GPU cores, but their higher clock frequency enables them to run tasks much faster. And for rendering, a higher core count is usually better.

The GPU, in comparison, has thousands of cores – 10,496 in the case of an Nvidia RTX 3090. These cores are, however, clocked at a much lower frequency than a CPU. Only the sheer number of cores compensate for their speed and, in some rendering scenarios, allow GPUs to overcome a CPU.

Quality

CPUs have fewer cores when compared to GPUs, however they’re far more versatile and designed to carry out complex instruction sets. This allows CPUs to run almost any algorithm with little effort and thus provide a better quality result.

In terms of quality, GPUs just can’t match CPUs. You’ll usually find that a GPU render has more noise in it.

RAM Benefits

CPUs have access to system memory. This allows them to use huge amounts of memory, which can be upgraded. The Threadripper 3990x can support 512 GB of DDR4 RAM. This enables the CPU to render huge amounts of data in a complex scene with many objects and details.

GPUs are limited by their built-in video RAM (VRAM). The latest Nvidia 3090 has just 24 GB of VRAM, which is more than enough for most users, but in complex scenes with many elements, it can become a bottleneck.

Complex Scenarios

CPUs can by design handle a variety of tasks. This is beneficial in workloads where the type of work isn’t consistent or there’s just too much to handle at a time.

GPUs are mostly limited by their hardware capabilities. They’re designed with a single purpose and are often used to run the same tasks repeatedly. Also, the RAM limitations coupled with slower cores limit their capacity to render various scenarios effectively.

Stability

CPUs are built into and well-integrated with the system. All the applications are built considering CPUs at the core of the operating system. And since CPUs have been used for a long time for rendering, most bugs have been ironed. This inherently leads to better overall system stability when you’re using CPUs for rendering.

GPUs are more prone to failure. Sudden power fluctuation, driver updates, and the lack of compatibility with certain systems, can cause poor and unstable GPU performance.

Speed

GPUs run tasks in parallel, which often translates to increased speed, as various elements of a scene can be rendered simultaneously. This results in a much faster turnaround and helps in the reiteration process. GPUs are also largely used in areas where real-time rendering is needed (like video games).

CPUs have fewer cores and are designed to run tasks sequentially. Thus, they’re typically slower than GPUs. A CPU is also restricted in the availability of its resources. As it has to execute many tasks, a CPU can’t utilize all of its hardware just for rendering This also contributes to a slower speed.

Regular Improvements

As we (appear to) approach the limits of Moore’s law, the leaps between each new generation of CPUs seem to be slowing. This could lead to a performance plateau over time and may even give the lead to the continuously improving GPUs.

In recent times, we’ve seen phenomenal leaps in GPU innovation, with companies like AMD and Nvidia both competing fiercely in this sector. The innovation cycle of GPUs is certainly faster than that of CPUs. And since it’s much easier to upgrade a GPU, you can expect a rise in rendering performance with each new generation.

Hardware Costs

GPUs are near the low end of the price spectrum when compared to performance-class CPUs. A good GPU, such as the RTX 3090, can cost around $1,500, whereas a strong CPU like the Threadripper 3990x carries a 5,000-dollar price tag.

GPUs also give you an edge in terms of upscaling. You can just attach another GPU to your pre-existing setup, and you’re ready. When you’re looking to upscale with CPUs, apart from the cost of the CPU, you’ll likely have to invest in further compatible hardware.

Rendering engines are another key factor when deciding between CPU and GPU rendering. Many rendering engines work solely on either a CPU or a GPU. Consequently, rendering engines also dictate which rendering software you can run on your system.

Rendering engines like Arnold, Corona, and 3Delight work on CPUs and produce slightly higher quality results. Meanwhile, renderers such as Blender Cycles, Octane, and Redshift, are optimized for GPUs.

YouTuber Andrey Lebrov has a great guide that exactly explains the differences and similarities between rendering engines, and how they might affect your workflow.

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The way you set up your system hardware can also affect your rendering performance. Maybe a good CPU would do better than dozens of GPUs, or maybe you can use a basic CPU with powerful GPUs for your workflow. This can be evaluated with some hardware benchmarks.

Two popular ways of judging rendering performances are Cinebench for CPU rendering and Octanebench for GPU rendering. They’re both the best benchmark standards in the industry. According to CG Director’s benchmarks, a multi-core CPU with a higher clock speed is a better choice for your workflow. The latest AMD 3rd generation CPUs have a serious edge in performance and are comparatively cheaper than the Intel CPUs. However, if you want the best of the best, the Threadripper 3990x is pretty much unbeatable when it comes to CPU rendering.

In the Octanebench benchmark, various GPUs are compared based on their rendering scores, performance, and price. The Nvidia RTX cards come out to be the kings in the rendering department. Upon careful evaluation, you can also observe that when you couple more GPUs together, you’re likely to get better performance and value from your GPUs, along with increased VRAM.

So, even if there’s a lot to consider, we can summarize the differences between CPU and GPU rendering depending on your needs:

• If your workflow demands speed, has less complexity, and is consistent in the work, a GPU rendering setup would do good for you. Besides lower hardware costs, the quality of the work is on par with CPU renders. GPU rendering would also suit a beginner’s profile in a better manner.
• If you’re someone who prioritizes quality, has a larger budget to spend on hardware, and can wait for quality results, CPU rendering is the way to go. Not only will you benefit from the quality of the renders, but the ability to process complex scenarios with ease will give you a competitive edge.

So, that does it. Both CPU and GPU rendering are the masters of their own universe. But the choice is down to you, your needs, and your possibilities.