RAM Types & Storage Devices
Key Takeaways
- DDR4 and DDR5 are the current RAM standards — DDR4 uses 288-pin DIMMs with a single notch, while DDR5 also uses 288 pins but with a different notch position, making them physically incompatible.
- DDR5 offers higher base speeds (starting at 4800 MT/s vs DDR4 at 2133 MT/s), on-die ECC, and improved power efficiency (1.1V vs 1.2V for DDR4).
- SSDs (Solid State Drives) have no moving parts, are faster, more durable, and silent compared to HDDs, but cost more per gigabyte; NVMe SSDs are the fastest storage option.
- RAID 0 (striping) improves performance but offers no redundancy, RAID 1 (mirroring) provides redundancy with 50% usable capacity, RAID 5 requires minimum 3 drives with one drive worth of parity, and RAID 10 combines mirroring and striping.
- ECC (Error-Correcting Code) RAM detects and corrects single-bit errors automatically and is required in servers and workstations for data integrity — it is NOT used in standard consumer desktops.
Last updated: March 2026
RAM Types & Storage Devices
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 |
| Capacity (per module) | Up to 16 GB | Up to 64 GB | Up to 128 GB |
| Channels | Dual | Dual/Quad | Dual (per module) |
| On-Die ECC | No | No | Yes |
Critical Exam Point: DDR generations are NOT interchangeable. Each generation has a different notch position on the module to physically prevent installation in the wrong slot. DDR4 will NOT fit in a DDR5 slot and vice versa.
RAM Types
| Type | Description | Use Case |
|---|---|---|
| DIMM | Full-size desktop module | Desktop PCs, servers |
| SODIMM | Small outline (laptop) module | Laptops, mini PCs |
| ECC | Error-Correcting Code | Servers, workstations (detects and corrects errors) |
| Non-ECC | Standard RAM without error correction | Consumer desktops and laptops |
| Registered (RDIMM) | Buffered for stability | Servers with many RAM modules |
| Unbuffered (UDIMM) | Standard without buffer | Consumer desktops |
RAM Installation Best Practices
- Match specifications — Install RAM that matches the motherboard's supported type, speed, and capacity
- Install in pairs — For dual-channel operation, install matching pairs in the correct color-coded slots
- Avoid mixing — Do not mix different speeds, sizes, or brands if possible (system will run at the slowest module's speed)
- Handle properly — Hold by edges, avoid touching gold contacts, use ESD protection
- Check BIOS — Verify RAM is recognized at the correct speed after installation
Storage Devices
HDD (Hard Disk Drive)
| Specification | 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 |
| Best For | Bulk storage, backups | Legacy laptops |
SSD (Solid State Drive)
| Form Factor | Interface | Max Speed | Connector |
|---|---|---|---|
| 2.5-inch SATA | SATA III | 600 MB/s | SATA data + power |
| M.2 SATA | SATA III | 600 MB/s | M.2 slot (B+M key) |
| M.2 NVMe (Gen 3) | PCIe Gen 3 x4 | ~3,500 MB/s | M.2 slot (M key) |
| M.2 NVMe (Gen 4) | PCIe Gen 4 x4 | ~7,000 MB/s | M.2 slot (M key) |
| M.2 NVMe (Gen 5) | PCIe Gen 5 x4 | ~12,000 MB/s | M.2 slot (M key) |
| U.2 | PCIe/NVMe | Varies | U.2 connector (enterprise) |
Exam Tip: An M.2 slot can support either SATA or NVMe drives depending on the keying. M key supports NVMe, B key supports SATA, and B+M key supports both. Check the motherboard specifications.
SSD vs. HDD Comparison
| Feature | SSD | HDD |
|---|---|---|
| Speed | Much faster (up to 12,000 MB/s NVMe) | Slower (100-200 MB/s) |
| Durability | No moving parts — shock resistant | Moving parts — fragile |
| Noise | Silent | Audible spinning and clicking |
| Power | Lower power consumption | Higher power consumption |
| Heat | Less heat (NVMe can run warm) | Moderate heat |
| Cost/GB | Higher | Lower |
| Capacity | Up to 8 TB (consumer) | Up to 20+ TB |
| Lifespan | Limited write cycles (TBW rating) | Mechanical wear over time |
RAID (Redundant Array of Independent Disks)
| RAID Level | Description | Min. Drives | Usable Capacity | Read Speed | Write Speed | Fault Tolerance |
|---|---|---|---|---|---|---|
| RAID 0 | Striping | 2 | 100% | Fast | Fast | None — 1 drive failure = total data loss |
| RAID 1 | Mirroring | 2 | 50% | Fast | Normal | 1 drive can fail |
| RAID 5 | Striping + Distributed Parity | 3 | (n-1) drives | Fast | Slower (parity calc) | 1 drive can fail |
| RAID 6 | Striping + Double Parity | 4 | (n-2) drives | Fast | Slowest (double parity) | 2 drives can fail |
| RAID 10 | Mirroring + Striping (1+0) | 4 | 50% | Fastest | Fast | 1 drive per mirror can fail |
RAID Summary for the Exam
- RAID 0: Maximum performance, zero fault tolerance — NEVER use for critical data
- RAID 1: Simple redundancy, easy to understand, 50% capacity overhead
- RAID 5: Most popular for servers — good balance of performance, capacity, and protection
- RAID 10: Best performance with redundancy — requires most drives (expensive)
Test Your Knowledge
What is the standard voltage for DDR5 RAM?
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B
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D
Test Your Knowledge
Which RAID level provides striping for performance but offers NO fault tolerance?
A
B
C
D
Test Your Knowledge
A client needs high-speed storage for video editing. Which interface provides the fastest possible consumer SSD speeds?
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B
C
D
Test Your Knowledge
Which RAID level requires a minimum of 3 drives and uses distributed parity for fault tolerance?
A
B
C
D