Comprehensive Guide to Motherboard Form Factors and Sizes: Mainstream and Recommended Options

Motherboard standards refer to the criteria that define the physical size, shape, expandability, mounting hole positions, and power connector layout of a motherboard, which is the base of a computer.

Depending on the motherboard standard, the number of PC parts that can be installed will change, and if the motherboard does not match the PC case standard, it cannot be physically installed.

Therefore, knowing what kinds of standards exist, which standards are mainstream today, the sizes of each standard, and how many parts can be installed for each standard will make it easier to select parts.

This article also explains how to choose a motherboard from the perspective of motherboard standards, part names, performance, and compatibility.

≫ Related article: How to Choose a Motherboard for a Custom PC [Performance / Features / Compatibility]

あわせて読みたい

PC Parts Estimation & Compatibility Check Tool

Automatically checks each component you need when selecting parts for a custom-built PC—perfect for beginners.

What Are Motherboard Standards?

Motherboard standards are criteria that determine the physical size, expandability, and compatibility with PC cases of a motherboard.

The Mainstream Motherboard Standards Today

The physical size of a motherboard is very important when choosing one, as it determines whether it will fit in a computer case.

Each motherboard standard has a set size, and the most common standards today are as follows:

• Extended ATX (E-ATX)
• ATX
• MicroATX
• Mini-ITX

Among these, ATX is the most widely used and has the largest number of products.

It is compatible with many PC cases, and its size and the types and number of parts it can accommodate make it a very user-friendly standard.

The next most used is MicroATX, which is about one size smaller than ATX.

Because it is smaller, the types and number of parts that can be installed are fewer, so expandability is lower. However, it fits in compact PC cases, making it popular among users who want to build a smaller computer.

Specific sizes and features will be explained later.

Expandability Differs by Standard

Motherboard expandability refers to the ability to add extra PC parts to enhance performance and features.

In simple terms, it means how many slots and connectors are available for installing parts.

A motherboard that can accommodate many different parts has high expandability, while one with fewer slots has low expandability.

The CPU slot is usually just one, but the number of memory, M.2, PCI Express slots, SATA connectors, and so on can vary, and this number changes depending on the expandability.

These slots and connectors require physical space, so larger motherboards tend to have more slots and connectors.

On the other hand, smaller motherboards can only have the minimum necessary number of slots.

For example, if building a custom PC for video editing, one might install a 1TB NVMe SSD in the M.2 slot as the main storage.

However, without actually editing videos, it is hard to know how quickly storage will fill up, so 1TB may not be enough.

By considering the possibility of future upgrades, it is possible to choose a motherboard with high expandability, such as one with two or three M.2 slots.

In this way, even if the basic performance meets the intended use, it is important to have a certain level of expandability (enough slots) to handle various situations.

Compatibility with PC Cases Is Necessary

In the end, all parts including the motherboard must fit inside the PC case, so it is necessary to check which motherboard standards the PC case supports.

For PC cases, larger cases generally support multiple standards such as ATX, Micro-ATX, and Mini-ITX.

On the other hand, small PC cases may only support Mini-ITX.

Since motherboard standards have different physical sizes and the number of parts that can be installed changes, some may think that choosing a larger motherboard is always better.

However, since the motherboard must fit in the PC case, this balance must be considered.

For example, if a compact case is desired due to installation space or personal preference, it may be necessary to choose a smaller motherboard standard to match.

Therefore, it is important to consider the size and design of the PC case together with the expandability of the motherboard when deciding which motherboard standard to choose.

Types, Sizes, and Expandability of Motherboard Standards

This section explains the types, sizes, and expandability of motherboard standards.

First, here is a summary list of standards, followed by a look at the features and expandability of the current mainstream motherboard standards.

List of Motherboard Standards

In recent years, ATX, MicroATX, Mini-ITX, and E-ATX have become the mainstream for custom PCs, and other standards are rarely used.

In fact, motherboards of other standards are often no longer sold.

Although many motherboard standards have appeared, many are no longer manufactured due to lack of demand or because they were not widely accepted by users.

Therefore, for custom PC building, it is enough to know the mainstream standards, and the other standards can just be thought of as “Oh, such things exist.”

Proprietary refers to motherboard standards that are uniquely designed and manufactured by specific companies.

These motherboards are usually used only in specific devices or systems and are different from standard formats like ATX or MicroATX.

Therefore, they are often not compatible with general PC cases and usually cannot be installed.

ATX

The ATX standard was established by Intel in 1996 and is currently the most widely used motherboard standard for desktop PCs.

Most mid-tower and full-tower PC cases support it.

ATX motherboards are 244 × 305mm in size and feature many expansion slots and ports, making them highly expandable.

• Memory: 4 slots (sometimes 2 slots, server models may have 8 or 12 slots)
• M.2 SSD: 2–5 slots
• SATA connectors: 4–6 (server models may have 10 or 12)
• PCI Express x16: 2–3 slots
• PCI Express x1: 1–3 slots
• PCI Express x4: sometimes 1 or 2 slots

There are many compatible PC cases, and the standard does not limit the range of choices, and there is enough expandability for future upgrades.

Therefore, for those building a custom PC for the first time, it is easy to choose and assemble, making it a recommended option.

MicroATX

MicroATX was established in 1995 and is a balanced standard that is smaller than standard ATX motherboards but still offers sufficient expandability.

It is often supported by mini-tower and larger (including mid-tower and full-tower) PC cases.

MicroATX motherboards are 244 × 244mm squares. While not as expandable as ATX, they are sufficient for general part configurations.

• Memory: 2–4 slots (server models may have 6 or 8 slots)
• M.2 SSD: 1–3 slots
• SATA connectors: 4–6 (server models may have 8, 10, or 12)
• PCI Express x16: 1–2 slots
• PCI Express x1: 1–2 slots

Like ATX, there are many compatible PC cases, making it easy to include as an option.

It is also ideal for those who want to build a PC in a case that is a bit more compact than a mid-tower.

Mini-ITX

Mini-ITX was established in 2001 by Taiwanese semiconductor manufacturer VIA and is a very compact motherboard standard mainly used for small desktop PCs.

It is popular among users who prefer small PC cases and do not mind sacrificing some expandability for a compact, space-saving PC.

Mini-ITX motherboards are 170 × 170mm squares, making them even smaller than MicroATX.

They are about 5cm smaller than MicroATX, so the number of slots is not sufficient, giving the impression of being the bare minimum.

• Memory: 2 slots (server models may have 4 slots)
• M.2 SSD: 1 or 2 slots
• SATA connectors: 2 or 4 (server models may have 2–12)
• PCI Express x16: 1 slot

If expansion is needed later, expandability is low, so it may be difficult.

Also, not only are the slots and connectors on the motherboard limited, but if a small PC case is used, the number of SATA SSDs and HDDs that can be installed is also limited, making upgrades difficult.

Even in mid-tower PC cases, Mini-ITX is often supported, but the motherboard will be small compared to the case.

When assembling a custom PC, a smaller motherboard is easier to work with, but if the case has a glass panel to show the inside, it may look a bit empty, so be careful.

Extended ATX

Extended ATX (E-ATX) is a motherboard standard based on ATX, expanded to a larger size and is one of the ATX derivative specifications, established by Intel.

It is mainly used for high-performance PCs and servers and is designed for systems that require multiple graphics cards and large amounts of memory.

Like ATX, it is compatible with mid-tower and full-tower PC cases.

Extended ATX motherboards are 330 × 305mm, about 10cm wider than the 244 × 305mm ATX.

• Memory: 4 slots (server models may have 8, 12, 16, 18, or 24 slots)
• M.2 SSD: 3–7 slots
• SATA connectors: 4–8 (server models may have 10 or 14)
• PCI Express x16: 2–5 slots
• PCI Express x1: 0–1 slot

Although the number of products is the smallest among the major motherboard standards, they are not so rare as to be impossible to find.

Depending on the CPU socket, there are products that support consumer CPUs like the Core i series and Ryzen series, but many sockets are for server and workstation CPUs like Xeon and Ryzen Threadripper.

Summary: For First-Time Custom PCs, ATX and MicroATX Are the Best Choices!

This article explained the types of motherboard standards, mainstream standards, sizes, features by standard, and approximate number of slots.

Here is a summary of the key points again.

There are many different standards, but the four that are currently mainstream are ATX, MicroATX, Mini-ITX, and E-ATX.

Therefore, when choosing a motherboard for a custom PC, it is basically enough to understand the features and expandability of these four and select the one that suits the needs.

If a large PC case is acceptable, it may be better to choose a larger motherboard for future expandability.

With the knowledge and skills to customize a custom PC, it is common to want to add more parts after purchase.

On the other hand, if there are restrictions on where the computer can be placed, or if the preferred design happens to be a small case, a smaller motherboard must be chosen, sacrificing expandability.

With a general part configuration, it is possible to assemble a PC even with low expandability, but it is better to assume that future upgrades will not be possible.

In the end, there is no single best choice, so consider the situation and decide which motherboard standard is best.

This article also explains how to choose a motherboard from the perspective of motherboard standards, part names, performance, and compatibility.

≫ Related article: How to Choose a Motherboard for a Custom PC [Performance / Features / Compatibility]

あわせて読みたい

PC Parts Estimation & Compatibility Check Tool

Automatically checks each component you need when selecting parts for a custom-built PC—perfect for beginners.