This guide will focus on mining motherboards.
What are mining motherboards? They are PC motherboards that are specifically designed to run multiple GPU's at the same time for mining.
Fun fact - they can actually be used as a regular PC motherboards although I would not recommend it.
Why would you want mining motherboards? Standard mining rigs use at the minimum 6 GPU's at one time. Some mining rigs can go up to 19 or even more!
They are designed to save you money - less computers, more GPU's. Every mining rig needs a motherboard, CPU, RAM, and Memory. If you could run one mining rig with 12 GPU's instead of two miners that run 6 each, you just saved money on a second motherboard, CPU, ram, memory like SSD or HDD and so on.
There is another benefit - the manufactures know which parts of the motherboard work the hardest and invest in more durable capacitors. Also, many times the settings are all perfect for mining right out of the box (Like 4G Decoding and so on).
They are more expensive, compared to standard motherboards for two reasons, one, they are less common and less produced which increase their price. Two, they usually have multiple PCI-E Express ports to support all those GPU's.
It depends on your setup, but you can save couple hundred bucks (sometimes more) by using one rig compared to two.
There are some drawbacks... for example, if your rig has an issue and goes offline, now you have TONS OF GPU's offline comparing to only 6 gpu's that are offline. Another drawback is that it's sometimes hard to find them, or they are out of stock, or their price goes higher than MSRP.
For first timers I would NOT recommend a mining motherboard. You can actually grab a Ready-To-Mine rig case that can hold 8 GPU's and it basically have everything you need and no assembly required.
If you are a pro, you can save tons of money and have a more streamline mining operation using less computers. Also, less computers mean less power consumption from the CPU, Ram and SSD. Although they usually take a tiny amount of power. I was recording 17W to 50W per rig, especially when using very simple CPU's like the Celeron G5905.
Pay attention to what kind of CPU is compatible with your mining motherboard. Some of them use AMD CPU's, and some use Intel. Also check what kind of CPU's they support.
For example - The ASUS Prime Z390-P LGA1151 mining motherboard only supports 8-9 gen Intel LGA1151 CPU's and would not work with any other CPU's! (Sometimes they have bios update to use newer CPU's but the socket always have to match, is this example it's LGA1151).
I do have one last trick out of my hat - this trick will save you tons of money and might unlock you to have many many GPU's on regular consumer motherboards. The PCI-E Express 1X to 4 PCI-E 16X Adapter. This little guy will expand one PCI-E Express (or full) lane, into 4 lanes! All you need to do is to use the USB PCI-E Riser and you are good to go. Some other settings might be needed but there is many success stories around this product.
I would personally try this method before paying too much on a mining motherboard. BUT! the convenience, reliability and plug and play features that the mining motherboards might benefit you in ways beyond this guide, so don't be quick to disregard their use in your mining farm.