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Samsung 990 EVO vs. WD Black SN850X: Which PCIe 4.0 SSD Should You Buy?
Choosing between the Samsung 990 EVO (and EVO Plus) and the WD_BLACK SN850X comes down to a fundamental architectural decision: dedicated DRAM cache versus power-efficient DRAM-less HMB. We compare real-world transfer speeds, PS5 gaming suitability, laptop thermals, and live pricing across Amazon, Best Buy, and Newegg to determine which SSD belongs in your system.
Tech Deal Compass editorial · NVMe SSD Head-to-Head Battle · 8 min read
Prices refreshed every morning at 6:00 AM EST (Updated October 19, 2026)
AT A GLANCE · THE VERDICTWD_BLACK SN850X Wins for Gaming & Heavy Writes; Samsung 990 EVO Wins for Laptops & Thermals
When comparing similarly priced 1TB, 2TB, or 4TB drives, the WD_BLACK SN850X is the superior performance drive. Its dedicated DDR4 DRAM cache, faster 7,300 MB/s sequential speeds, and consistent sustained write rates make it the clear winner for PlayStation 5 consoles, primary PC boot drives, and video editing workflows.
However, the Samsung 990 EVO (and 990 EVO Plus) is the smarter choice for laptops and portable systems. By eliminating onboard DRAM and using an ultra-efficient controller, it draws nearly 40% less peak power, runs dramatically cooler, and features a unique hybrid PCIe 5.0 x2 mode that conserves PCIe lanes on modern motherboards.
Live Price Face-Off: Today’s Verified Retailer Deals
Our pricing engine compares real-time inventory and pricing for both SSDs across Amazon, Best Buy, and Newegg every morning. Below are today's lowest verified prices:
Contender A · SamsungBest for Laptops & Thermals
High-efficiency DRAM-less SSD utilizing Host Memory Buffer (HMB). Features innovative hybrid PCIe 4.0 x4 and PCIe 5.0 x2 compatibility, running exceptionally cool under sustained daily workloads.
- Max Speed: Up to 5,000 MB/s (990 EVO) / 7,250 MB/s (990 EVO Plus)
- DRAM: DRAM-less (64MB Host Memory Buffer)
- Interface: PCIe 4.0 x4 / PCIe 5.0 x2 Hybrid
- Peak Power: ~4.5W (Excellent battery life)
Contender B · Western DigitalOverall Performance Winner
Flagship PCIe 4.0 gaming drive equipped with dedicated DDR4 DRAM cache, blazing 7,300 MB/s sequential speed, and sustained multi-queue-depth random throughput.
- Max Speed: Up to 7,300 MB/s read / 6,600 MB/s write
- DRAM: Dedicated DDR4 Cache (1GB per 1TB)
- Interface: PCIe 4.0 x4
- Peak Power: ~8.5W (Requires heatsink under load)
Direct Specification Comparison
| Technical Metric | Samsung 990 EVO | Samsung 990 EVO Plus | WD_BLACK SN850X | Round Winner |
|---|
| DRAM Cache | DRAM-less (HMB) | DRAM-less (HMB) | Dedicated DDR4 DRAM (1GB/TB) | WD SN850X |
| Max Sequential Read | 5,000 MB/s | 7,250 MB/s | 7,300 MB/s | WD SN850X |
| Max Sequential Write | 4,200 MB/s | 6,300 MB/s | 6,600 MB/s | WD SN850X |
| Random 4K IOPS (Read/Write) | 700K / 800K | 1,000K / 1,350K | 1,200K / 1,100K | Tie / WD SN850X |
| PCIe Interface Modes | Gen 4x4 or Gen 5x2 | Gen 4x4 or Gen 5x2 | Gen 4x4 only | Samsung 990 EVO |
| PS5 Compatibility | Below Sony 5,500 MB/s Spec | Passes (7,250 MB/s) | Exceeds (~6,500 MB/s in PS5) | WD SN850X (Officially Licensed) |
| Peak Power Consumption | ~4.5W (Ultra-efficient) | ~4.9W | ~8.5W (Runs hot) | Samsung 990 EVO |
| Heatsink Requirement | Optional (Bare drive is fine) | Optional | Mandatory under heavy load | Samsung 990 EVO |
| Endurance (TBW per TB) | 600 TBW | 600 TBW | 600 TBW | Tie (600 TBW / 1TB) |
Deep Architectural Analysis: The 5 Deciding Factors
1. The DRAM Cache Difference (Why It Matters)
The most consequential architectural difference between these two drives is the memory cache. An SSD uses a Flash Translation Layer (FTL) table to map logical block addresses from your operating system to physical locations on the NAND flash chips.
The WD_BLACK SN850X carries a physical DDR4 DRAM chip soldered onto the PCB (1GB of DRAM per 1TB of storage). This gives the controller immediate, nanosecond access to the entire mapping table. Under heavy random reads and writes (such as operating system boots, database operations, or uncompressing massive game archives), the drive maintains consistent low latency.
In contrast, the Samsung 990 EVO is a DRAM-less SSD. To keep costs down and power consumption minimal, it uses NVMe Host Memory Buffer (HMB) technology, borrowing up to 64MB of your system’s main RAM over the PCIe bus. While HMB performs admirably for quick burst transfers and daily web browsing, sustained random multi-tasking or heavy write loads can cause minor latency spikes once the SLC cache fills up.
2. PlayStation 5 Gaming Benchmark
If you are expanding storage for a PlayStation 5 console, this comparison is decisive:
- WD_BLACK SN850X: Universally recognized as one of the best PS5 expansion SSDs. It routinely formats at roughly 6,500 MB/s inside the PS5 benchmark, well above Sony's 5,500 MB/s recommended speed. WD also sells the drive with an integrated low-profile heatsink (and an officially licensed PS5 edition, the SN850P) that slips straight into the PS5 expansion slot without modification.
- Samsung 990 EVO: Formats at approximately 5,000 MB/s inside the PS5, which technically falls below Sony’s recommended 5,500 MB/s threshold. While games will install and play, you will see a Sony warning message upon formatting, and future titles heavily utilizing DirectStorage and high-bandwidth asset streaming may experience micro-stuttering. (Note: The newer 990 EVO Plus meets the speed threshold at ~6,500 MB/s in PS5, but still lacks dedicated DRAM).
3. Thermals, Power Draw & Laptop Battery Life
The table flips completely when considering laptop upgrades:
The WD_BLACK SN850X is a high-power desktop beast. Under continuous write activity, it consumes up to 8.5W of power and generates significant heat. In a thin-and-light laptop without room for a heatsink, the SN850X will quickly reach its 80°C thermal throttle threshold, severely reducing transfer speeds and draining laptop battery life.
The Samsung 990 EVO is an efficiency marvel. Its streamlined controller and DRAM-less design pull less than 4.5W at full throttle, and drop into micro-watt deep sleep states when idle. It runs cool enough to operate comfortably under thin copper foil heatspreaders found in ultrabooks and portable consoles like the ASUS ROG Ally or Steam Deck (with an M.2 2280 adapter).
4. Sustained Write Speeds & SLC Cache Exhaustion
Both drives utilize pseudo-SLC caching to accelerate incoming writes. However, how they behave once that fast buffer is filled during a massive 150GB+ transfer is very different:
- WD SN850X: Features a massive dynamic SLC cache. Even when writing beyond the cache, its BiCS5 TLC NAND paired with onboard DRAM maintains sustained write speeds between 1,600 MB/s and 1,800 MB/s.
- Samsung 990 EVO: Uses Samsung’s Intelligent TurboWrite 2.0. Burst speeds are snappy, but once the SLC buffer is exhausted on continuous writes, speeds drop to roughly 1,000 MB/s while it simultaneously clears the buffer and writes to TLC blocks.
5. The PCIe 5.0 x2 Hybrid Innovation
Samsung included an ingenious feature on the 990 EVO: hybrid PCIe 4.0 x4 and PCIe 5.0 x2 lane switching.
Most modern motherboard chipsets and CPUs have limited PCIe 5.0 lanes. On motherboards supporting Gen 5 x2 slots, the 990 EVO can achieve its full 5,000 MB/s speed using only two physical PCIe lanes instead of four. This frees up two PCIe lanes for secondary expansion cards, high-speed networking adapters, or capture cards without reducing the drive’s bandwidth. The SN850X is strictly a PCIe 4.0 x4 drive.
Which One Should You Buy?
🏆 Buy the WD_BLACK SN850X if:
- You are upgrading storage on a PlayStation 5.
- You need a primary boot drive (C: drive) for heavy Windows multi-tasking.
- You edit 4K/8K video, compile large software projects, or move 100GB+ files frequently.
- Your desktop motherboard has a built-in metal M.2 heatsink to manage thermals.
- Both drives are within $10 to $15 of each other in price.
🔋 Buy the Samsung 990 EVO if:
- You are upgrading a laptop or ultrabook and prioritize battery life and cool thermals.
- You need a secondary game-library drive (D: drive) where games are read rather than heavily written.
- You have a modern motherboard and want to utilize a PCIe 5.0 x2 slot to conserve lane bandwidth.
- You find the 990 EVO on sale at a $25+ discount compared to the SN850X.
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