PC Hardware and Components

Week of 2026-09-22 · Download .docx

Objectives

Identify the function of each major PC component: CPU, RAM, HDD/SSD, PSU, motherboard, and chipset.
Explain why RAM is volatile and contrast it with non-volatile storage technologies.
Compare HDD and SSD storage technologies and identify the correct expansion slot for each device type.
Select the correct thermal interface material and explain its role in CPU cooling.
Describe the role of BIOS/UEFI firmware during the system boot sequence.

Key terms

CPU: Central Processing Unit — the processor that fetches, decodes, and executes all program instructions; performance measured in GHz and core count.
Volatile memory: Memory that loses all stored data when power is removed. RAM is the primary example in modern computers.
Non-volatile memory: Memory that retains stored data without power. Examples: ROM, SSD (NAND flash), HDD (magnetic platters).
RAM: Random Access Memory — high-speed volatile storage that holds active programs and data while the computer is running.
SSD: Solid-State Drive — a storage device using NAND flash memory chips; no moving parts; faster and more durable than HDDs.
HDD: Hard Disk Drive — a storage device using spinning magnetic platters and a motorized read/write actuator arm.
PSU: Power Supply Unit — converts AC mains voltage from the wall outlet to regulated DC voltages (+12V, +5V, +3.3V) used by PC components.
Motherboard: The main printed circuit board that physically connects and coordinates all system components via buses, slots, and connectors.
Chipset: A set of integrated circuits on the motherboard (the PCH on modern platforms) that manages data routing between the CPU, RAM, storage, and I/O peripherals.
PCIe x16: Peripheral Component Interconnect Express — the high-bandwidth expansion slot standard used for discrete graphics cards and NVMe SSDs.
BIOS/UEFI: Firmware stored in flash memory on the motherboard; initializes hardware components and runs POST before handing control to the OS boot loader.
Thermal paste: A thermally conductive compound applied between the CPU heat spreader and heatsink to eliminate air gaps and improve heat transfer.
NVMe: Non-Volatile Memory Express — a storage protocol that connects NAND flash drives directly to the PCIe bus via an M.2 slot, reaching 3,500–7,000+ MB/s.

The concept

Every personal computer, regardless of manufacturer or form factor, is built from a small set of standardized components that each perform a specific role. Understanding what each component does — and how they interact — is the foundation of the CompTIA A+ certification.

**The CPU: Execution Engine**

The CPU (Central Processing Unit) is responsible for executing every software instruction that runs on the machine. It operates by repeating the fetch-decode-execute cycle: it fetches an instruction from RAM, decodes what operation is required, and executes it. This cycle happens billions of times per second on each core. Modern CPUs have multiple cores so they can execute several instruction streams in parallel. Performance is measured by clock speed (GHz — billions of cycles per second), core count, and the amount and speed of on-chip cache memory.

**Memory: Volatile vs. Non-Volatile**

RAM (Random Access Memory) is volatile: DRAM cells store data as electrical charge that dissipates without continuous power. Every byte in RAM is erased the instant the computer loses power. This is why saving your work to disk matters — the document in RAM disappears on power loss while the saved copy on the SSD remains intact.

In contrast, storage devices are non-volatile. HDDs use spinning magnetic platters where data is encoded as magnetic north/south orientations that persist indefinitely without power. SSDs use NAND flash memory — billions of transistors that trap electrons in a floating gate to represent bits — which also retains data without power. SSDs have no moving parts, making them faster, quieter, and more shock-resistant than HDDs.

**The Motherboard and Power Delivery**

The motherboard is the backbone of every PC. It physically connects and electrically interfaces the CPU, RAM, storage devices, expansion cards, and all I/O ports. The chipset on the motherboard manages the routing of data between these subsystems, controlling which component can use which bus at which time.

The PSU (Power Supply Unit) converts the 120V or 240V AC power from the wall into the DC voltages components require: +12V for the CPU, GPU, and storage drive motors; +5V for USB ports and legacy logic; and +3.3V for memory controllers and some I/O circuits. These three rails are the standard ATX voltage specification.

**Cooling and BIOS/UEFI**

The CPU generates significant heat during operation. A heatsink mounted directly on the CPU pulls that heat away by conduction, and a fan then dissipates it into the case airflow. Thermal paste fills the microscopic imperfections between the CPU heat spreader and the heatsink contact plate — replacing trapped air (a poor thermal conductor) with a metal-oxide compound that conducts heat far more effectively.

Before the operating system loads, the motherboard's BIOS or UEFI firmware runs the POST (Power-On Self-Test) to verify that the CPU, RAM, video output, and storage controllers are functional. If POST succeeds, the firmware locates the OS boot loader on the selected storage device and transfers control to it.

Worked examples

Example 1: Diagnosing a storage decision: A student asks whether to use an HDD or SSD for their A+ practice machine. The choice depends on the use case. HDD: large capacity (4 TB) at low cost, ~150 MB/s read, has moving parts — good for archiving files not actively used. SSD: higher cost per GB, 500–7,000 MB/s read depending on SATA vs. NVMe, no moving parts — the correct choice for the OS and active applications. Recommendation: install the OS on an NVMe or SATA SSD for fast boot and app launch; add an HDD only if bulk storage is needed. For a certification lab machine, a single SSD is sufficient.

Example 2: Identifying the correct slot: A technician is adding a new graphics card to a desktop PC. Step 1 — locate the longest PCIe slots on the motherboard; these are the x16 slots. Step 2 — confirm the slot is x16 by counting 16 contacts or reading the motherboard manual. Step 3 — seat the card in the top PCIe x16 slot (closest to the CPU) for maximum bandwidth and proper power delivery from the 6- or 8-pin PCIe connectors from the PSU. Step 4 — connect the power connectors before closing the case and verify with a POST boot that the card is detected in BIOS/UEFI.

Common mistakes

Assuming any M.2 slot is NVMe. M.2 is a physical slot form factor that supports both SATA and NVMe protocols. An M.2 SATA SSD is still limited to 600 MB/s. Check the drive label for 'PCIe NVMe' or look for the M-key notch only (vs. B+M-key on SATA).
Thinking RAM and storage are interchangeable. RAM is volatile and holds currently running data; storage is non-volatile and holds saved data. They serve different purposes at different speeds and cannot substitute for each other.
Skipping thermal paste on CPU reinstallation. Removing a heatsink breaks the old paste bond. Reinstalling without fresh paste traps air gaps, raises CPU temperatures, and causes thermal throttling or long-term damage.
Plugging a GPU into a PCIe x1 slot. A modern GPU requires a PCIe x16 slot for full bandwidth. A PCIe x1 slot is too short to seat most graphics cards and would severely bottleneck performance even on cards that physically fit.
Confusing the PSU's 24-pin motherboard connector with the CPU's 8-pin EPS connector. Both must be connected for the system to boot. Missing the 8-pin CPU connector causes the system to fail POST even though power is present.

Self-check

Try each question before reading the answer. Answers at the bottom of this page.

1. Which component retains data after the computer is powered off?

RAM
CPU cache
SSD
Video RAM

2. Which DC voltage rail from an ATX PSU is primarily used to power the CPU and GPU?

+3.3V
+5V
+12V
+24V

3. A technician reinstalls a CPU heatsink without applying thermal paste. What is the most likely result?

The system will not POST
CPU temperatures will rise and thermal throttling will occur
The CPU will immediately burn out
RAM will fail to initialize

4. Which firmware program runs POST and initializes hardware before the OS loads?

GRUB
MBR
BIOS/UEFI
POST

5. What distinguishes NVMe SSDs from SATA SSDs in terms of connection and speed?

NVMe uses the SATA controller and reaches 600 MB/s
NVMe connects via USB and reaches 2 GB/s
NVMe connects via PCIe lanes and reaches 3,500–7,000+ MB/s
NVMe uses spinning platters and reaches 150 MB/s

Self-check answers

1. C — SSD uses non-volatile NAND flash memory that retains data without power. RAM and CPU cache are volatile and lose data on power loss.
2. C — +12V is the primary rail for power-hungry components including the CPU (via the EPS connector) and GPU (via PCIe power connectors).
3. B — Without thermal paste, air gaps between the CPU and heatsink insulate heat, causing CPU temperatures to rise. The CPU will throttle (reduce clock speed) to protect itself from overheating.
4. C — BIOS/UEFI firmware stored on the motherboard runs POST and initializes all hardware components before locating and launching the OS boot loader.
5. C — NVMe SSDs bypass the SATA controller by connecting directly to PCIe lanes via an M.2 slot, allowing sequential reads of 3,500–7,000+ MB/s — more than 10× SATA's 600 MB/s ceiling.

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