This page describes various types of case layouts and form factors that you will see throughout the rest of the wiki. Every case is different, so we will try to keep things as general as possible here, while still providing some prominent examples.
Some time ago, traditional ATX tower cases moved their power supply to the bottom of the chassis, leaving the upper area for the motherboard, PCI/PCIe cards, cables and coolers. You will find this often referred to as the “Tower” layout, as it has most in common with traditional Mid-tower cases, just shrunk down to ITX form factors. Some common cases with this layout are the Fractal Design Define Nano S, and the NZXT H200/H210i. Because they leave the entire “basement” to the Power Supply (and sometimes hard drives), this is not a terribly compact layout, and average case size reflects this.
The primary innovation in the original Small Form Factor cases (like the NCase M1) was moving the power supply to be adjacent and forwards of the motherboard. By shrinking the motherboard to Mini-ITX, while still having 300mm GPUs, you had a cavity in the top front of the case where a power supply could go. The power supply is then fed by an extension cord from the back of the system.
These new ITX layouts are called “Classic”, “Traditional”, or “M1-style” layout (after the first case that pioneered it). They are also notable for not using riser cables to connect PCIe devices (like other, more compact layouts). Common modern cases that follow this layout are the Cooler Master NR200, the Fractal Design Era ITX, and many others.
The idea of a sandwich layout case is to take the Classic layout, where your ITX motherboard and power supply are next to each other, and then move your GPU to the reverse side of the case using a PCIe riser cable. This creates a side-by-side layout, where the middle spine of the case is “sandwiched” between the motherboard and PSU on one side, and the GPU on the other. This significantly reduces the total required space by the components because the GPU height (distance from the PCIe edge connector to the top of the IO bracket or beyond) no longer dictates the case width. Therefore, you can narrow the case width while still allowing for (relatively) large GPUs.
This layout was originally pioneered by the Dan A4-SFX, and so sometimes this layout is referred to as the “A4” layout. Innovations on the sandwich layout include adding additional vertical height to the case to accommodate top-mounted radiators and All-in-One coolers (such as the Sliger SM570), creating modular “top hats” to add more capability (like the Louqe Ghost S1), and turning the sandwich layout vertically to create a smaller desk area (like the Phanteks Evolv Shift or the NZXT H1).
To further shrink the total possible space required, some cases eschew the use of SFX power supplies in favor of Flex-ATX power supplies. These short in height, but long in length power supplies originated in the server world, where they were commonly used in 1U servers (hence their limited height). By placing this at the bottom of the case while placing the rest of the “sandwich” above, and while limiting the length of GPUs, you can create significantly smaller cases. An ITX motherboard is 170mm square, and a Flex ATX PSU is 150mm long (with cables coming out the back), so by limiting your sandwiched GPU to 170mm or less, you can create cases that are as wide as the Flex ATX Power Supply but are only 170mm wide and 210mm tall (with obvious additional space required for panels and other keep out zones).
This makes half-sandwich cases, like the Velkase Velka 3 or the SGPC K39v2, extremely small, often less than 5 liters in volume. It does significantly restrict GPU length, however.
A more recent modification of the Half-Sandwich was used in the Intel Ghost Canyon NUC case, where a “Compute Element” board (essentially a laptop motherboard and cooling solution in a PCIe card form factor) was placed along side a short GPU, sitting atop a Flex ATX power supply.
An alternatively approach to miniaturization from the Sandwich design is to leverage a PCIe riser to turn the GPU 90 (or 270) degrees to place it in line with the motherboard, instead of placing it behind. This creates a case that is very narrow, but long and tall like a pizza box. These cases are called “Console” cases because their shape is analogous to game consoles or other home theater equipment. These cases can be placed flat on a surface for a wide footprint or turned on its side for a vertical orientation. Some cases use a 90-degree riser to make the GPU “face” the opposite direction, while other cases using a longer riser cable to go behind the GPU so its front is the same as the motherboard and PSU. Many commodity cases from Silverstone, as well as the Fractal Design Node 202 utilize this layout. The NFC Skyreach 4 Mini also uses a Console-style layout.
These cases are ones which generally do not allow for a discrete GPU, hence they are referred to as “APU” cases based on AMD’s naming of their integrated CPU/GPU processors. However, APU cases are equally appropriate for Intel processors with integrated graphics. By not providing space for GPUs, the case size can become roughly the size of the ITX (or Micro-STX in some cases) motherboard, sometimes with room for a power supply. Some cases require the use of external power supply adapters or “bricks” while others make space for specialized or custom power supplies for “brickless” builds. The InWin Chopin is an example of an APU case.
These are not so much cases, as they are a plate for the motherboard, standoffs for components like a PCIe cards, and sometimes a place to attach a power supply. Otherwise, they are open to the elements. Sometimes this is done for aesthetic reasons, other times for thermals, and other times for ease of swapping out components on a test bench. Examples would be the XTIA PROTO or the OpenBenchtable Mini.