A+ Core 1 3.5: Motherboard Form Factors — Class Notes

2026-09-27 · class-notes, a-plus, comptia, messer, hardware, motherboard, form-factors, atx, micro-atx, mini-itx

Full class notes for A+ Core 1 3.5: choosing between ATX, micro-ATX and Mini-ITX by size, slots, power and mounting.

Class notes · Professor Messer A+ Core 1 (220-1201) · Section 3, lesson 5

Quick reference: the short version of this lesson lives in the A+ Core 1 Section 3 resource sheets. This lesson shares objective 3.5 ("Given a scenario, install and configure motherboards, CPUs, and add-on cards") with the Motherboard expansion slots lesson — that one covered the add-on cards; this one covers the board itself.

Learning objectives

By the end of these notes you should be able to:

1. Explain why a motherboard's form factor matters — size, component layout, power and cooling.
2. Name the three form factors the A+ expects you to know and rank them by size.
3. Describe ATX: what the name stands for, roughly when it appeared, and how its main power connector changed.
4. Describe micro-ATX and how it relates to ATX (mounting points, power, slot count).
5. Describe Mini-ITX and why its mounting compatibility lets it fit an ATX case.
6. Choose an appropriate form factor for a given scenario.

1. Why form factor matters

Whether you are buying a machine or building one, you face a lot of choices, and one of the first is the form factor of the motherboard — its standardised size and layout. Very different computers can hold the same kinds of parts. A big desktop tower and a small box sitting next to a television both contain a CPU, memory, storage, a network connection and so on. What separates them is their footprint: the tower is large, the media box is small, and the boards inside them cannot be the same shape.

Four things drive the differences between one motherboard and another:

• Physical size. The most obvious difference, and the one the form-factor name captures.
• Component layout. Larger boards have room for more components and more flexibility in how they are arranged; smaller boards force compromises.
• Power. Most boards use a standard main power connector, but not every board uses exactly the same one, so it is worth checking.
• Airflow and cooling. Every board generates heat, and the cooling system has to keep up with it — a consideration that gets harder as boards and cases shrink.

There are, per Wikipedia, more than forty motherboard types in existence. The good news is that for the A+ you only need three of them.

Exam tip: objective 3.5 is written "Given a scenario". You will not be asked to recite dimensions so much as to choose: which of these three boards suits a media centre, and which suits a video-editing desktop? Match the board to the job.

2. The three you need

For the exam, focus on ATX, micro-ATX and Mini-ITX. In size order, ATX is the largest, micro-ATX sits in the middle, and Mini-ITX is the smallest of the three. They are closely related — micro-ATX and Mini-ITX both descend from the ATX standard and deliberately keep parts of it — which is what makes them easy to compare.

Note (beyond this lesson): the transcript compares the three only in relative terms. For reference, the usual maximum sizes are ATX ~305 x 244 mm, micro-ATX ~244 x 244 mm, and Mini-ITX ~170 x 170 mm. The exam leans on the relative ordering rather than the exact millimetres.

Shared mounting points, drawn nested:

+-------------------------------+
|  o                         o  |
|     +---------------------+   |
|     |  o             o    |   |
|     |    +-----------+    |   |
|     |    | o       o |    |   |
|     |    |           |    |   |
|     |    | o       o |    |   |
|     |    +-----------+    |   |
|     |  o             o    |   |
|     +---------------------+   |
|  o                         o  |
+-------------------------------+

Outer board = ATX, middle = micro-ATX, inner = Mini-ITX; each o is a mounting screw point. Because the smaller boards reuse ATX screw positions, a smaller board bolts into a case built for a larger one. (Schematic, not to scale.)

3. ATX — Advanced Technology Extended

ATX stands for Advanced Technology Extended. It is a long-lived standard that has been around since 1995, and although it has seen many revisions over the years, the current version remains very similar to the original.

The part that has changed most is the main power connector. Early ATX boards used a 20-pin connector for main system-board power; more modern boards use a 24-pin connector. (You will meet the 24-pin main connector again in the Computer power lesson, 3.6.)

An ATX board is physically large, and that size buys capacity: room for a generous number of expansion slots and, in the example Messer shows (a Gigabyte GA-P67A board), four memory slots, with the CPU socket in the middle. It is worth fixing the relative sizes of the CPU socket, the memory slots and the expansion slots in your mind on the full-size board, because those same components look proportionally different once you move to a smaller form factor.

In the real world: "more slots" is a tendency of the larger board, not a fixed rule of the standard. Two ATX boards can differ in how many slots the manufacturer fits — but the extra area is what makes more slots possible.

4. micro-ATX

micro-ATX is very similar in layout to ATX, just slightly smaller. Two similarities matter most:

• Mounting points. micro-ATX places its mounting holes at the same positions as a full-size ATX board (a subset of them), so it fits the same cases and standoffs.
• Power connectors. It uses the same power connectors as full-size ATX.

That close compatibility is exactly why micro-ATX is popular: it follows the ATX standards yet fits a much smaller board.

The trade-off is capacity. Shrinking the board means deciding which components survive the cut. The micro-ATX board Messer shows (an MSI H81M-P33) has a single expansion slot and just two memory slots, against the larger board's four memory slots and multiple expansion slots. When you go smaller, you give up expansion room.

5. Mini-ITX

If you need something genuinely small, look at an ITX board — specifically Mini-ITX, one of the smallest members of the ITX family.

Despite being a small board, Mini-ITX keeps the same mounting screw points as a traditional ATX motherboard. The practical consequence is neat: you can take a case designed for an ATX board and install a Mini-ITX board inside it, because the screw holes line up.

Its very small size makes it ideal wherever space is tight or the machine has one job to do: a streaming media device beside a television, a small-office box, or any single-task computer. Fewer slots is the price, but for an appliance-style build that is rarely a problem.

5.1 Worked example — picking a board for the scenario

Two builds land on your bench on the same day.

1. A 4K video-editing desktop. This needs a powerful graphics card (a long PCIe x16 card), plenty of RAM across several memory slots, and maybe a capture card and extra storage controllers. Capacity is everything, so choose ATX — the most expansion and memory slots, the most room for cooling.
2. A streaming box for the living room. This runs one application beside the TV and must be small and quiet. It needs almost no expansion. Choose Mini-ITX — smallest footprint, fits neatly into a tight space, and still bolts into standard mounts if you reuse a case.
3. A general small-office PC that should stay cheap and compact but keep a little room to grow (one add-in card, a RAM upgrade later)? micro-ATX is the middle ground — ATX-compatible, smaller, a slot or two to spare.

The reasoning is always the same: start from what the machine must do, work out how much expansion and cooling that implies, then pick the smallest form factor that still meets it.

6. Security perspective

This is a hardware-selection lesson, so its security relevance is indirect — but two points are worth keeping:

• A standard footprint cuts both ways. Shared mounting points and layouts are convenient for you and for an attacker: a tampered board of the same form factor drops into the same chassis and looks right, which is the physical side of a supply-chain or "evil maid" swap. Physical asset checks — does this machine have the board, slot count and populated headers you expect? — are how you catch that, so knowing the normal layout is a defender's baseline.
• Small single-purpose boxes are still endpoints. Mini-ITX appliances beside a TV, at a reception desk or in a comms cupboard are physically exposed, often run unattended and unpatched, and are easy to overlook in an inventory. Treat them as untrusted devices on the network, patch and segment them, and don't let "it's just the media box" leave one unmanaged on the corporate LAN.

Slot count also has a quiet security dimension: a board with fewer expansion slots simply offers fewer internal card-based attack points, but also less room for defensive hardware (an extra monitored NIC, add-in security modules) — a trade-off, not a win either way.

Summary

• Form factor is a motherboard's standardised size and layout; it is driven by size, component layout, power and cooling.
• The A+ wants three: ATX (largest), micro-ATX (middle), Mini-ITX (smallest).
• ATX = Advanced Technology Extended, from 1995; main power went from 20-pin to 24-pin; largest, most slots.
• micro-ATX shares ATX's mounting points and power connectors but is smaller with fewer slots.
• Mini-ITX is the smallest common ITX board and keeps ATX-compatible mounting, so it fits an ATX case; ideal for small, single-task machines.
• Objective 3.5 is scenario-based: choose the smallest board that still gives the expansion and cooling the job needs.

Glossary

Review questions

1. In one sentence, what does "form factor" mean for a motherboard?
2. List the four practical factors that differentiate one motherboard from another.
3. Name the three form factors the A+ expects, in size order.
4. What does ATX stand for, and roughly when did it appear?
5. How did the ATX main power connector change over time?
6. Give two things micro-ATX keeps the same as full-size ATX.
7. What does micro-ATX give up compared with ATX, and why?
8. Why can a Mini-ITX board be installed in a case built for ATX?
9. Scenario: a customer wants a tiny, quiet machine to stream video next to their TV. Which form factor, and why?
10. Scenario: a customer wants a workstation for 4K video editing with a big GPU and lots of RAM. Which form factor, and why?
11. True or false: a larger form factor guarantees more expansion slots. Explain.
12. Objective 3.5 begins "Given a scenario". What does that tell you about how this material is tested?

Answer key

1. Its standardised physical size and component layout. The form factor sets what fits and where.
2. Physical size, component layout, power, and airflow/cooling. These drive the choice between boards.
3. ATX (largest), micro-ATX (middle), Mini-ITX (smallest). Three of forty-plus real types.
4. Advanced Technology Extended; 1995. Long-lived, little changed since.
5. From a 20-pin main connector on early boards to a 24-pin on modern ones. The rest of ATX stayed largely the same.
6. The mounting points and the power connectors. That compatibility is why micro-ATX is popular.
7. Expansion and memory slots (fewer of each), because the smaller board has less room. Shrinking forces trade-offs.
8. It uses ATX-compatible mounting screw points, so the holes line up with an ATX case. Same standoffs, smaller board.
9. Mini-ITX — smallest footprint, fits a tight space beside the TV, needs almost no expansion. Right tool for a single-task box.
10. ATX — the most expansion and memory slots and the most room for cooling. Capacity is the priority.
11. False — it makes more slots possible, but the manufacturer decides how many to fit. Size is an enabler, not a guarantee.
12. It is tested by choosing the right board for a situation, not by reciting specs. Match the board to the job.