Understanding the Real Differences Behind Two Fast Gen4 NVMe SSDs
On paper, the WD Blue SN5100 and Samsung 990 EVO Plus look very similar. Both are PCIe Gen4 NVMe SSDs with read speeds around 7,000 MB/s and strong overall performance. But the real story is inside the drives. Their memory design, controller strategy, and NAND type create meaningful differences in how they behave under different workloads.
This comparison explains what actually separates them and which type of user each drive fits best.
1. Interface and Physical Design
| Feature | WD Blue SN5100 | Samsung 990 EVO Plus |
|---|---|---|
| Form Factor | M.2 2280 | M.2 2280 |
| Interface | PCIe Gen4 x4 | PCIe Gen4 x4 |
| NVMe Version | NVMe 1.4 | NVMe 1.4 |
Both drives use the same physical size and interface. Compatibility with modern desktops, laptops, and gaming systems is essentially identical. The difference comes from the internal architecture.
2. NAND Flash Technology: QLC vs TLC
This is the most important difference.
WD Blue SN5100: QLC NAND
The SN5100 uses QLC (Quad Level Cell) NAND, which stores 4 bits of data per cell.
Characteristics of QLC NAND:
- Higher storage density
- Lower manufacturing cost per gigabyte
- Lower endurance than TLC
- Slower native write speed
To compensate, the SN5100 uses a large SLC cache. Part of the QLC memory temporarily operates in faster SLC mode. This allows the drive to show very high burst write speeds.
What this means in real use:
- Excellent short burst performance
- Very good for gaming, OS use, and everyday tasks
- During very long writes, once the SLC cache fills, speeds drop to native QLC levels
This design favors capacity and value, not long-duration heavy write workloads.
Samsung 990 EVO Plus: TLC NAND
The 990 EVO Plus uses TLC (Triple Level Cell) NAND, storing 3 bits per cell.
Characteristics of TLC NAND:
- Faster native write performance than QLC
- Higher endurance
- More stable under sustained workloads
- Slightly higher cost per gigabyte
Samsung combines TLC NAND with an advanced controller and DRAM cache to maintain performance consistency.
What this means in real use:
- High peak speeds similar to SN5100
- Better sustained performance during long file transfers
- More consistent behavior under heavy workloads
TLC NAND is considered the balanced performance and durability standard in performance SSDs.
3. Controller and Cache Strategy
SN5100 Design
- Controller optimized for QLC
- Large dynamic SLC write cache
- May use DRAM or Host Memory Buffer depending on model
This architecture delivers strong burst numbers but relies heavily on caching behavior. Performance can vary depending on how full the drive is and how long a write workload continues.
990 EVO Plus Design
- Samsung in-house performance controller
- Dedicated DRAM
- TLC NAND reduces reliance on short-term caching
Because TLC is inherently faster, the drive maintains high performance even after the SLC-style cache region is exceeded.
4. Sequential Performance
Both drives operate near the limits of PCIe Gen4.
| Metric | SN5100 | 990 EVO Plus |
|---|---|---|
| Sequential Read | Around 7,000 MB/s class | Around 7,000 MB/s class |
| Sequential Write | Very high burst speeds | Very high and more sustained |
In short tests, performance looks nearly identical. The difference shows during long continuous writes.
5. Random Performance and System Responsiveness
Random I/O affects boot times, application loading, and general system feel.
- SN5100 delivers strong random performance for mainstream use.
- TLC NAND in the 990 EVO Plus helps maintain more consistent random performance during heavier multitasking or sustained workloads.
Both feel fast, but the Samsung drive tends to be more stable under stress.
6. Sustained Workload Behavior
This is where the NAND type matters most.
| Scenario | SN5100 (QLC) | 990 EVO Plus (TLC) |
|---|---|---|
| Short file transfers | Excellent | Excellent |
| Game loading | Excellent | Excellent |
| Large single transfers | Starts fast, may slow later | Stays fast longer |
| Heavy continuous writes | Noticeable speed drop after cache | More consistent speed |
QLC drives are optimized for peak performance bursts. TLC drives are optimized for longer performance consistency.
7. Endurance and Lifespan
Because QLC stores more bits per cell, each cell wears out faster.
- SN5100 has lower total write endurance than TLC drives.
- 990 EVO Plus has higher endurance and is better suited for write-heavy environments.
For typical users, both drives can last many years. Professionals writing large volumes of data daily benefit more from TLC.
8. Thermal and Power Behavior
Under heavy sustained load:
- TLC-based drives generally maintain more stable performance and thermals.
- QLC drives can show more fluctuation once the cache system is stressed.
Proper airflow or a heatsink is recommended for either drive in high-performance systems.
Final Verdict
Both are fast Gen4 SSDs, but they serve slightly different priorities.
Choose WD Blue SN5100 if:
- You want strong speed at a lower cost per GB
- Your usage is gaming, OS, and general productivity
- Most workloads are short or mixed
Choose Samsung 990 EVO Plus if:
- You move large files often
- You run heavier workloads like video editing or data work
- Long-term endurance and sustained performance matter
In simple terms:
SN5100 focuses on value and high burst speed using QLC with caching.
990 EVO Plus focuses on consistency and durability using TLC NAND.