Let’s begin with the basics

Rendering absolutely hammers the processor so the CPU is arguably the most important component when choosing rendering hardware.
Each CPU features multiple processors (called cores). The more cores you have, the faster the render.
As a rule of thumb, doubling the number of cores halves the rendering time.

The GHz of the CPU is also important. To get a rough idea of comparative performance of chips from the same family of CPUs,
multiply the GHz by the number of cores. However, when choosing a CPU for a workstation, don’t forget a high GHz processor
is essential for general system performance (Operating System, CAD and 3D graphics).
Therefore, it is important to find the right balance i.e. do not choose a CPU with lots of cores but a very low GHz.

Most (but not all) workstation-class CPUs feature Intel Hyper-threading (HT), a virtual core technology that turns each physical CPU core
into two virtual cores. So a quad core processor with HT actually has eight virtual cores (or threads).
HT can boost rendering performance by up to 15% so it’s an important consideration when choosing a CPU.

Memory is also critical. Go for ECC memory to protect against crashes (you don’t want your overnight renders to fail).
N.B. ECC is only available on Intel Xeon, not Intel Core.

Adding more GB won’t make your render go faster. Instead, just ensure you have enough to handle complex scenes.
If you run out of memory, rendering data will need to be moved in and out of hard drive swap space, which can be slow.
Use fast Solid State Drives (SSDs) to move data quickly.

The GPU is only used for interactive 3D graphics in most rendering software. However, a growing number can use the GPU for rendering
(e.g. V-Ray RT, Nvidia Iray, Lightworks Iray+ and AMD FireRender).

The Options

You can render on pretty much any type of laptop or desktop computer but choose a workstation-class machine
as the components and cooling are designed specifically for compute intensive workloads.
Laptops typically peak at 4 CPU cores and 32GB RAM so are best suited to entry-level rendering.

Those serious about rendering will need a desktop workstation. These come with one or two CPUs, each with multiple CPU cores.
Single CPU workstations feature anywhere from 2 to 18 cores and up to 256GB RAM.

Dual CPU workstations have anywhere from 8 to 36 cores and up to 1TB RAM.

For hardcore users, distributed rendering takes rendering to a whole new level. It shares render jobs across multiple networked computers.
This can be an ad hoc network of workstations or a dedicated render farm with 10s or 100s of render nodes, each with dozens of CPU cores.