Search r/buildapc or r/pcmasterrace for “BX500 vs A400” and you’ll find the same thread reposted monthly for years. The top comment is almost always some version of “buy whichever is cheaper.” That’s mostly correct — these are the two cheapest branded SATA SSDs you can buy — but a few real differences decide who should grab which, and when you should skip both.
Spec sheet vs reality
| Crucial BX500 | Kingston A400 | |
|---|---|---|
| Capacities | 120GB–4TB | 120GB–1.92TB |
| Interface | SATA 6Gb/s, 2.5″ 7mm | SATA 6Gb/s, 2.5″ 7mm |
| DRAM cache | None | None |
| Controller / NAND | SMI SM2258XT/2259XT; Micron TLC or QLC depending on capacity and revision | Usually Phison S11; NAND varies wildly between batches |
| Rated sequential | 540/500 MB/s | Up to 500/450 MB/s (120GB writes rated just 320) |
| Warranty / endurance | 3 years; ~80TBW at 240GB, ~120TBW at 480GB | 3 years; ~80TBW at 240GB, ~160TBW at 480GB |
Both saturate the SATA bus on reads in a fresh benchmark, and both feel identical for the things SATA SSDs actually get bought for: booting Windows in ~15 seconds, loading games within a second or two of a premium drive, making a 10-year-old laptop usable again. The differences only appear under sustained load.
The failure mode Reddit actually hits: sustained writes
Neither drive has DRAM, and both rely on an SLC write cache — a slice of the NAND pretending to be faster memory. Once that cache fills, write speeds fall off a cliff. On QLC-based units, sustained writes can drop to 40–80 MB/s — slower than a 7200rpm hard drive.
Where you notice this in practice:
• Cloning your old drive. A 500GB clone that starts at 500 MB/s can slow to a crawl partway through and take an hour-plus. Use a cheap USB-to-SATA adapter, start the clone, walk away.
• Installing large games. A 150GB game downloading while the drive simultaneously decompresses files is exactly the mixed workload DRAM-less drives handle worst.
• Moving big video files or VM images regularly.
Booting, browsing, office work, and game load times? You will never feel the difference between these and a drive costing twice as much.
The component lottery
The deeper Reddit complaint applies to both brands. Kingston is notorious for shipping the A400 with whatever controller and NAND was cheapest that quarter — two A400s bought a year apart can be meaningfully different drives. Crucial does the same thing more quietly; early BX500s were TLC, later revisions and larger capacities shifted toward QLC. This is why review benchmarks from launch year don’t necessarily match what’s on the shelf now, and why one user’s “my A400 is great” and another’s “mine died in a year” can both be true. There’s no solid evidence one model fails more than the other overall — both carry 3-year warranties and no power-loss protection, so keep backups either way.
What Reddit actually recommends
Read enough threads and a clear pattern emerges:
1. If you’re strictly choosing between these two for a game library or a light-use machine, buy whichever is cheaper. Prices on budget 2.5-inch SATA SSDs swing weekly, and the BX500 and A400 trade “cheapest” status constantly.
2. Given a slight preference, more users lean BX500 — marginally higher rated write speeds and somewhat more predictable internals.
3. The most-upvoted answer in most threads: skip both if the price gap is small. When a DRAM-equipped drive like the Crucial MX500 or Samsung 870 EVO sits within $10–15 of the budget drives — which happens often at 1TB — it’s the better buy for a primary drive. You get DRAM, a 5-year warranty instead of 3, and sustained writes that don’t collapse.
Which one for which job
Secondary game drive, media storage, reviving an old laptop or office PC: buy the cheaper one today. The BX500 vs A400 debate genuinely does not matter here — endurance ratings like 120TBW mean writing 40GB every day for eight years, which no game library touches.
Main OS drive for a machine you work on daily: lean BX500 if the two are price-equal, but check the MX500’s price first. At 1TB and up, the gap is frequently small enough that paying it is the obvious move.
Regularly moving large files, video editing scratch disk, anything write-heavy: neither. This is the one workload where these drives genuinely underperform a spinning disk mid-transfer, and no amount of “it’s fine for most people” changes that.
One last detail worth checking at checkout: capacity naming. At the ~1TB tier, the BX500 gives you a full 1TB while the A400 tops out at 960GB — roughly 40GB less usable space, which can erase a few dollars of price advantage on its own.
