Motherboards & Form Factors

CompTIA A+ Core 1 (220-1101) • Domain 3.0 Hardware

Key Concepts: ATX/mATX/ITX Chipsets Expansion Slots Connectors BIOS/UEFI

What is a Motherboard?

The motherboard (also called mainboard or system board) is the primary circuit board that connects all computer components together. It provides power distribution, data pathways, and manages communication between CPU, RAM, storage, and peripherals.

A+ Exam Tip: Know the different form factors and their dimensions. The motherboard form factor determines which cases and power supplies are compatible!

Form Factors

ATX

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12" × 9.6"

Full-size desktop

Micro-ATX

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9.6" × 9.6"

Compact desktop

Mini-ITX

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6.7" × 6.7"

Small form factor

E-ATX

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12" × 13"

Workstation/Server

Form Factor	Dimensions	Expansion Slots	Use Case
ATX	12" × 9.6"	7 slots	Standard desktops, gaming PCs
Micro-ATX (mATX)	9.6" × 9.6"	4 slots	Budget builds, office PCs
Mini-ITX	6.7" × 6.7"	1 slot	HTPCs, compact builds
E-ATX	12" × 13"	7+ slots	Workstations, servers, enthusiast

Expansion Slots

Slot Type	Bandwidth	Common Uses
PCIe x16	Up to 64 GB/s (PCIe 4.0)	Graphics cards, high-speed NVMe
PCIe x8	Up to 32 GB/s (PCIe 4.0)	RAID cards, some GPUs
PCIe x4	Up to 8 GB/s (PCIe 4.0)	NVMe SSDs, network cards
PCIe x1	Up to 2 GB/s (PCIe 4.0)	Sound cards, USB expansion
M.2	Varies by key	NVMe/SATA SSDs, WiFi cards

PCIe Generations: PCIe 3.0 = 1GB/s per lane, PCIe 4.0 = 2GB/s per lane, PCIe 5.0 = 4GB/s per lane

Common Motherboard Connectors

Power Connectors

⬛⬛⬛⬛⬛⬛

24-pin ATX Main Power

⬛⬛

8-pin CPU (EPS12V)

⬛

4-pin CPU (ATX12V)

Internal Connectors

          SATA Data

          7-pin connector

          HDDs, SSDs, optical

          Front Panel

          Power/Reset/LED

          Case buttons & LEDs

          USB Headers

          USB 2.0/3.0/Type-C

          Front panel USB ports

Fan Headers

          3-pin Fan

          Voltage-controlled speed

          Basic fans

          4-pin PWM Fan

          Pulse-width modulation

          CPU coolers, smart fans

Chipsets

The chipset controls data flow between the CPU, memory, storage, and peripherals. It determines which features the motherboard supports.

Intel Chipsets (Example)

Chipset	Target
Z790	Enthusiast (overclocking)
B760	Mainstream
H770	Business/Office

AMD Chipsets (Example)

Chipset	Target
X670E	Enthusiast (overclocking)
B650	Mainstream
A620	Budget

BIOS vs UEFI

Legacy BIOS

Basic Input/Output System
16-bit, text-based interface
MBR partition scheme
2.2 TB max boot drive
Keyboard-only navigation

UEFI

Unified Extensible Firmware Interface
32/64-bit, graphical interface
GPT partition scheme
9.4 ZB max boot drive
Mouse support, Secure Boot

UEFI Features: Secure Boot prevents unauthorized OS loading, Fast Boot speeds startup, and network boot (PXE) is enhanced.

CMOS & BIOS Battery

The CMOS (Complementary Metal-Oxide Semiconductor) stores BIOS/UEFI settings. A CR2032 battery maintains these settings when the PC is unpowered.

Symptoms of Dead CMOS Battery:

Date/time resets on every boot
BIOS settings reset to defaults
"CMOS Checksum Error" message

Rear I/O Panel Connectors

          USB Ports

          USB 2.0, 3.0, 3.1, Type-C

          Peripherals, storage

          Video Outputs

          HDMI, DisplayPort, VGA

          Integrated graphics

          Network

          RJ-45 (Ethernet), WiFi antenna

          LAN connectivity

          Audio

          3.5mm jacks, S/PDIF

          Speakers, mic

          PS/2

          Purple (KB), Green (Mouse)

          Legacy peripherals

          Thunderbolt

          USB-C form factor

          High-speed, daisy-chain

Knowledge Check

Q1: What are the dimensions of a standard ATX motherboard?

Q2: Which expansion slot provides the highest bandwidth for graphics cards?

Q3: What type of battery maintains CMOS settings?

Q4: How many expansion slots does a typical Mini-ITX motherboard have?