RAM Types & Storage Devices

CompTIA A+ 220-1201 & 220-1202

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1 Introduction & Exam Overview

About the CompTIA A+ Certification Exam Domains & Study Strategy

2 Core 1 Domain 1: Mobile Devices (13%)

Laptop Hardware & Components Laptop Features & Display Types Mobile Device Connectivity & Accessories Mobile Operating System Features Mobile Device Synchronization & Data Transfer

3 Core 1 Domain 2: Networking (23%)

TCP/IP Fundamentals & the OSI Model Common Ports & Protocols Wireless Networking Standards Network Hardware & Devices Network Configuration & Internet Connections Network Types & Topologies

4 Core 1 Domain 3: Hardware (25%)

Cables & Connectors RAM Types & Storage Devices Motherboards, CPUs & Power Supplies Printers & Multifunction Devices Peripheral Devices & Expansion Cards Network Cable Tools & Testing

5 Core 1 Domain 4: Virtualization & Cloud Computing (11%)

Virtualization Concepts Cloud Computing Models & Services Client-Side Virtualization in Practice

6 Core 1 Domain 5: Hardware & Network Troubleshooting (28%)

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7 Core 2 Domain 1: Operating Systems (28%)

Windows Editions & Features Windows Administrative Tools & Utilities Windows Command Line & PowerShell macOS & Linux Basics Windows Networking & File Sharing Windows Installation & Upgrade Methods

8 Core 2 Domain 2: Security (28%)

Physical & Logical Security Measures Malware Types & Threat Mitigation Wireless & Network Security Encryption & Data Protection

9 Core 2 Domain 3: Software Troubleshooting (23%)

Windows OS Troubleshooting Mobile OS & Application Troubleshooting Browser & Application Troubleshooting

10 Core 2 Domain 4: Operational Procedures (21%)

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RAM Types & Storage Devices

Key Takeaways Explain This Topic AI

DDR4 and DDR5 both use 288-pin DIMMs but have notches in different positions, making them physically incompatible — you cannot mix generations in one board.

DDR5 starts at 4800 MT/s, runs at 1.1V, and adds on-die ECC, versus DDR4 at 2133 MT/s base and 1.2V.

SSDs have no moving parts and are faster, quieter, and shock-resistant; NVMe (PCIe) drives are far faster than SATA SSDs, which cap near 600 MB/s.

RAID 0 = striping (no redundancy), RAID 1 = mirroring (50% usable), RAID 5 = striping with one parity drive (min 3), RAID 10 = mirror + stripe (min 4).

ECC RAM detects and corrects single-bit errors automatically and is used in servers/workstations — not standard consumer desktops.

Last updated: June 2026

RAM (Random Access Memory)
DDR (Double Data Rate) Generations

Specification DDR3 DDR4 DDR5
Pin Count (DIMM) 240 288 288
Pin Count (SODIMM) 204 260 262
Voltage 1.5V 1.2V 1.1V
Base Speed 800 MT/s 2133 MT/s 4800 MT/s
Max Speed 2133 MT/s 3200+ MT/s 8400+ MT/s
Per-Module Capacity up to 16 GB up to 64 GB up to 128 GB+
On-Die ECC No No Yes

Critical Exam Point: DDR generations are NOT interchangeable . DDR4 and DDR5 are both 288-pin, but the notch (key) is in a different position , so DDR5 will not seat in a DDR4 slot. The exam loves the trap that identical pin count implies compatibility — it does not. On-die ECC in DDR5 is internal error correction and is NOT the same as full side-band ECC found on server modules.

RAM Types

Type Description Use Case
DIMM Full-size desktop module Desktops, servers
SODIMM Small-outline laptop module Laptops, mini PCs, NUCs
ECC Error-Correcting Code Servers, workstations
Registered (RDIMM) Buffered for stability Servers with many modules
Unbuffered (UDIMM) No buffer Consumer desktops
RAM Channels & Installation

Populating matched pairs in the correctly color-coded slots enables dual-channel (or quad-channel on HEDT boards), which roughly doubles memory bandwidth. A single stick or a mismatched pair forces single-channel mode and lower performance.

Match specs — type, speed, and voltage to the motherboard QVL
Install in matched pairs in the labeled A2/B2 slots (consult the manual)
Avoid mixing speeds/sizes — the system runs at the slowest module's timings
Handle by the edges , use ESD protection, never touch gold contacts
Enable XMP/EXPO in UEFI so RAM runs at its rated speed, not the JEDEC base
Storage Devices
HDD (Hard Disk Drive)

Spec 3.5-inch (Desktop) 2.5-inch (Laptop)
Technology Spinning magnetic platters Spinning magnetic platters
RPM 5400 / 7200 / 10000 / 15000 5400 / 7200
Interface SATA III (6 Gbps) SATA III (6 Gbps)
Capacity up to 20+ TB up to 5 TB
Sequential Read 100–200 MB/s 80–160 MB/s

Higher RPM means faster access but more heat and noise; 15000 RPM drives are enterprise-only. HDDs win on cost-per-gigabyte for bulk storage and backups.

SSD (Solid State Drive)

Form Factor Interface Max Speed Keying / Connector
2.5-inch SATA SATA III ~550 MB/s SATA data + power
M.2 SATA SATA III ~550 MB/s B+M key
M.2 NVMe (Gen 3) PCIe 3.0 x4 ~3,500 MB/s M key
M.2 NVMe (Gen 4) PCIe 4.0 x4 ~7,000 MB/s M key
M.2 NVMe (Gen 5) PCIe 5.0 x4 ~12,000 MB/s M key
mSATA SATA III ~550 MB/s mSATA edge

Exam Tip: M.2 keying decides what a slot accepts. B key = SATA, M key = NVMe (PCIe x4), B+M key = the drive fits both kinds of slot. A SATA M.2 drive will physically seat in an M-key NVMe slot only if the slot is wired for SATA — always check the board manual. M.2 length codes like 2280 mean 22 mm wide x 80 mm long.

SSD vs. HDD

Feature SSD HDD
Speed Up to ~12,000 MB/s (NVMe Gen 5) 100–200 MB/s
Moving parts None — shock resistant Platters/heads — fragile
Noise Silent Audible spin/click
Cost/GB Higher Lower
Wear metric TBW (terabytes written) Mechanical MTBF

Never defragment an SSD — it adds wear with no benefit. Use TRIM instead, which the OS issues automatically to maintain write performance.

RAID (Redundant Array of Independent Disks)

Level Description Min. Drives Usable Capacity Fault Tolerance
RAID 0 Striping 2 100% None — any failure loses all data
RAID 1 Mirroring 2 50% 1 drive can fail
RAID 5 Stripe + distributed parity 3 (n−1) drives 1 drive can fail
RAID 6 Stripe + double parity 4 (n−2) drives 2 drives can fail
RAID 10 Mirror + stripe (1+0) 4 50% 1 per mirror set
RAID exam shortcuts

RAID 0 — max speed/capacity, zero protection. Never for critical data.

RAID 1 — simple mirror, survives one failure, 50% overhead.

RAID 5 — most popular server choice; good capacity efficiency with single-drive protection. Write penalty from parity calculation.

RAID 10 — best blend of speed and redundancy, but you only get half your raw capacity and need at least four drives.

Scenario: A small business wants maximum usable space with single-disk fault tolerance across four 4 TB drives. RAID 5 yields ~12 TB usable (n−1); RAID 10 would yield only ~8 TB.