Types of Computer Cases and Motherboard Factors

Before you start

Objectives: learn about the common types of computer cases, names and sizes of usual motherboard form factors and which motherboard fits which computer case.

Prerequisites: no prerequisites.

Key terms: types of computer cases, case size, full tower, mid tower, mini tower, slim line, small form factor, motherboard form factors, atx, micro atx, mini atx, mini itx, btx, nlx, riser card

Computer Cases

The most common system case type is the tower. Depending on the specific number of internal drive bays and the height of the tower, these cases can be further classified into mini-size, mid-size and full-size tower cases. One of the biggest considerations when choosing between case sizes is the number of slots and the number of devices we would like to add to those cases.

Full Tower

Full-tower cases are generally big with a height that is about or more than 30 inches (more than 76 cm). The number of internal drive bays inside these cases can be between 6 and 10.

Full Tower Case

Image 113.1 – Tower Computer Case

Mid Tower

Another case that might be a step down, would be classified as a mid tower case. Mid-tower cases are the most widely used computer cases. Mid Tower cases are about 18 to 24 (45 to 60 cm) inches high and they usually contain 2 to 4 internal drive bays and a similar number of external bays (for CD/DVD readers and similar).

Mid Tower Computer Case

Image 113.2 – Mid Tower Computer Case

Mini Tower

Mini-tower usually have up to 2 or sometimes 3 internal drive bays. Mini-cases normally stand at a height of 12 to 18 inches (30 to 45 cm). Expandability is a problem with these cases.

Mini Tower Computer Case

Image 113.3 – Mini Tower Computer Case

Slim Line Case

Slim Line Computer Case

Image 113.4 – Slim Line Computer Case

Slim line cases are simply tower cases turned on their sideways. They can hold a monitor on top of the case.

Small Form Factor (SFF) Case

Small form factor or SFF cases are custom cases that are designed to minimize the spatial volume of a desktop computer. SFFs are available in a variety of sizes and shapes, including shoe boxes, cubes, and book-sized PCs.

Small Form Factor Computer Case

Image 113.5 – Small Form Factor Computer Case

Motherboard Form Factor

There’s one important consideration we need to be aware of when choosing the case size and that is the size of the motherboard. They need to match. The size of the motherboard is often called the Form Factor and there are several standards. The form factor identifies the size of the circuit board, the location of the slots as well as the location of the faceplate that comes out the back of the computer. The form factor also identifies the location of the holes that are used to mount the motherboard into the system case. For example, the full tower has more than enough room to fit an ATX motherboard. Mid-tower case can also accommodate an ATX motherboard in most cases.

ATX Form Factor (Full ATX)

Probably the most common form factor for a motherboard is the ATX form factor. The board is approximately 12″ x 9.6″ (30cm x 24cm).

ATX Form Factor

Image 113.6 – ATX Form Factor

Mini ATX

A mini-ATX motherboard is a slightly smaller variation of the full ATX size that measures 11.2″ x 8.2″ (28cm x 21cm). The main difference between ATX and mini-ATX is the number of buses and possibly memory slots on the motherboard. Mounting holes for both are located in the same place, making them interchangeable in most cases. A case that supports an ATX motherboard can also support mini-ATX motherboard.

Micro ATX

The micro-ATX form factor is an even smaller version of the ATX standard, with a maximum size of 9.6″ x 9.6″ (24cm x 24cm). The faceplate line up to the exact same position as in all other versions of ATX. System case that can hold an ATX motherboard can also hold micro ATX motherboard. The smaller mid or mini tower cases would likely be too small for a full ATX motherboard but should accommodate micro ATX motherboard. The terms mini-ATX and micro-ATX are often used interchangeably.

Micro ATX Form Factor

Image 113.7 – Micro ATX Form Factor

Flex ATX

The size of Flex ATX is 9” x 7.5” (22,9 cm x 19,1 cm). It is derived from Micro ATX and is used in small computer cases.

Flex ATX

Flex ATX Form Factor

Mini ITX

Going down in size we have a mini ITX motherboard with a maximum size of 6.7″ x 6.7″ (17cm x 17cm). Notice that there is a single expansion slot and the motherboard itself is considerably smaller than the ATX and even the micro ATX. Also notice that the faceplate still line up and the hole positions still match the ATX hole positions. Theoretically we could take this micro ITX motherboard and place it inside a full tower case. However we usually use a small form factor case for this motherboard.

Mini ITX Form Factor

Image 113.8 – Mini ITX Form Factor


Em ITX dimensions are 17 cm x 12 cm.


Em ITX Form Factor

Nano ITX

Measures of Nano ITX are 4.7″ x 4.7″ (12 cm x 12 cm). It is used with smaller devices like set-top boxes, car PCs, media centers, and other embedded devices.

Nano ITX

Nano ITX Form Factor

Pico ITX

The size of the Pico ITX is 3.9” x 2.8” (10 cm X 7,2 cm).

Pico ITX

Pico ITX Form Factor

Mobile ITX

Mobile ITX is the smallest form factor with the size of 2.4” x 2.4” (6 cm x 6 cm).

Mobile ITX

Mobile ITX Form Factor

The ATX form factor and its variations are the most common motherboard form factors.

DTX Form Factor

DTX form factor is intended for small form factor PCs, and is backward compatible with ATX form factor cases. Dimensions are 8” x 9.6” (20,3 cm x 24,4 cm).

DTX Form Factor

DTX Form Factor

Mini DTX

Mini DTX is a shorter version of DTX form factor. Dimensions are 8” x 6.7” (20,3 cm x 170 cm).

Mini DTX

Mini DTX Form Factor


SSI form factors were developed by SSI (Server System Infrastructure) forum, and are intended for dual or multi processor motherboards used in servers and or even workstations. SSI form factors were derived from ATX specification, so they have the same rear panel, IO connector area, and mounting holes. But, SSI form factors are larger than ATX, so SSI motherboards will not fit cases designed for standard ATX. The computer case has to be designed for larger than standard ATX form factor.
Three SSI form factors are CEB (Compact Electronics Bay), EEB (Enterprise Electronics Bay), and MEB (Midrange Electronics Bay). The smallest of them is SSI CEB, and the size is 12” x 10.5” (30,5 cm x 26,7cm).


SSI CEB Form Factor

SSI EEB (also called Extended ATX or E-ATX)

SSI EEB dimensions are 12” x 13” (30,5 cm x 33 cm).


SSI EEB Form Factor


The SSI MEB size is 16.2” x 13” (41,1 cm x 33 cm). It is longer in order to provide space for two additional CPU sockets.


SSI MEB Form Factor

BTX Form Factor

There are a few main differences with the BTX form factor. Notice that the faceplate is on the opposite end. Another difference is that the hole positions are different. Also, the processor socket is slightly rotated so that it is at an angle to the system board. This rotation is to aid in the airflow across the processor to assist in cooling the processor. The BTX motherboard will only fit within a system case that is designed for a BTX motherboard. In many cases this means that an ATX system case will not work with a BTX system board, although there are system cases that are able to accommodate both the ATX and the BTX form factors. The BTX form factor has not been widely adopted despite its improvements over ATX and related standards. As a result, the availability and variety of BTX-compatible components is limited.

BTX Form Factor

Image 113.9 – BTX Form Factor

NLX Form Factor

The NLX is an older style form factor that is not used very often anymore. We might see it in some older motherboards but it’s not likely to encounter it with newer motherboards.

NLX Form Factor

Image 113.10 – NLX Form Factor

NLX is an older form factor used for slimline desktop-style computers. NLX is an improvement over an even earlier LPX form factor. Notice that this motherboard has no expansion slots for the PCI or ISA bus. The NLX form factor is used in slim line cases that are very short.

NLX With Riser Card

Image 113.11 – NLX With Riser Card

In order to accommodate expansion cards we use a tab on the edge of the motherboard. We insert a Riser Card on the end of the motherboard. Riser Card is then used for expansion cards, so that now expansion cards lay flat rather than being perpendicular to the motherboard. The riser card does not have built-in ports for audio, joystick, USB, network or modem.


When choosing a system case, other than considering the size of the computer that we want, the most important thing is to match the motherboard form factor with the form factor supported by the computer case. The most common system case type is the tower. Tower cases are: Full tower, Mid tower and Mini tower. Slim line cases are simply tower cases turned on their sideways. Small form factor or SFF cases are custom cases that are designed to minimize the spatial volume of a desktop computer. The size of the motherboard is often called the Form Factor. The most common form factor for a motherboard is the ATX form factor. When considering the size of ATX we differentiate Full ATX, Mini ATX, Micro ATX, Flex ATX, Mini ITX, Em ITX, Nano ITX, Pico ITX, Mobile ITX. SSI CEB, SSI EEB, SSI MEB form factors are larger than ATX. When comparing with ATX, BTX form factor has the faceplate on the opposite side, hole positions are different and the processor socket is slightly rotated. The BTX motherboard will only fit within a computer case that is designed for a BTX motherboard. The NLX is an older style form factor that is not used very often anymore.