At sequential read speeds, moving 100GB takes 23.8 seconds on UFS 4.0, 23.3 seconds on UFS 4.1, and 9.3 seconds on UFS 5.0. Stepping from 4.0 to 4.1 saves half a second; stepping from 4.1 to 5.0 saves fourteen. The decimal digit and the integer digit in the generation label carry wildly different weight.
Smartphone storage labels tell you almost nothing beyond the fact that a bigger number is faster. Working only from what the manufacturers have published, here are the sequential speeds, transfer times, and package volumes of the three generations, calculated out.
UFS 4.0, 4.1 and 5.0 on published specs
Samsung announced UFS 4.0 in May 2022 with sequential read of 4,200MB/s, sequential write of 2,800MB/s, and a stated data bandwidth of 23.2Gbps. Power efficiency was given as 6.0MB/s of sequential read per milliamp, more than 45% better than UFS 3.1, with capacity up to 1TB and a package measuring 11mm × 13mm × 1.0mm.
UFS 4.1 came from SK hynix in May 2025, built on 321-layer NAND. Sequential read tops out at 4,300MB/s; random read and random write improved 15% and 40% respectively over the prior generation; thickness came down about 15% from the 238-layer product to 0.85mm; power efficiency improved 7%. It ships in 512GB and 1TB.
Samsung announced UFS 5.0 in June 2026. Per ZDNet Korea, it delivers 10.8GB/s sequential read and 9.5GB/s sequential write, more than 40% better power efficiency than UFS 4.1, a 7.5 × 13 × 0.9mm package, up to 1TB, with mass production in the fourth quarter.
| Standard | Sequential read | Sequential write | Power efficiency | Announced |
|---|---|---|---|---|
| UFS 4.0 (Samsung) | 4,200MB/s | 2,800MB/s | 45%↑ vs UFS 3.1 | May 2022 |
| UFS 4.1 (SK hynix) | 4,300MB/s | not disclosed | 7%↑ vs prior gen | May 2025 |
| UFS 5.0 (Samsung) | 10,800MB/s | 9,500MB/s | 40%↑ vs UFS 4.1 | June 2026 |
Every value here is as published by the manufacturer. UFS 4.1's sequential write is left blank because it was not disclosed, and since the vendors differ, the baseline for each power-efficiency claim differs by row.
How many seconds to move 100GB
Sequential speed is quoted in megabytes per second, so transfer time is simply capacity ÷ speed. Treating 100GB as 100,000MB gives the table below. A 20GB write, roughly one 4K film onto a phone, is included alongside.
| Standard | 100GB read (sec) | 100GB write (sec) | 20GB write (sec) |
|---|---|---|---|
| UFS 4.0 | 23.8 | 35.7 | 7.1 |
| UFS 4.1 | 23.3 | not disclosed | not disclosed |
| UFS 5.0 | 9.3 | 10.5 | 2.1 |
From UFS 4.0 to UFS 5.0, read time falls from 23.8 to 9.3 seconds, a 61% cut; write time falls from 35.7 to 10.5 seconds, a 71% cut. Write improved more because it started from further behind. UFS 4.0's write speed was 67% of its read speed; UFS 5.0's reaches 88%. The read-write asymmetry narrows as the generations advance.
These are theoretical figures. Real transfers are bound by the controller's SLC cache size, file fragmentation, thermal throttling, and the speed of whatever sits on the other end. Push large files continuously and speed drops off a step once the cache is exhausted. If you are moving files to a PC over a cable, the bottleneck usually lands on the interface rather than the storage — which is exactly where the fact that a USB-C cable's power rating and data speed are separate things starts to bite.
The bandwidth figure does not divide cleanly either. Divide UFS 4.0's 23.2Gbps by eight and you get 2.9GB/s, yet the published sequential read is 4.2GB/s. Read the figure as per-lane and, given UFS bonds two lanes, the total becomes 46.4Gbps or roughly 5.8GB/s — and 4.2GB/s lands at 72% of that, which fits. Interface bandwidth and real sequential speed are not the same number; protocol overhead and NAND-side limits fill the gap.
Why 4.0 to 4.1 buys only 2.4%
On sequential read alone, 4,200MB/s to 4,300MB/s is a 2.4% gain. That looks thin for a generation bump, but sequential is not where UFS 4.1 spent its effort. The real gains are 15% on random read and 40% on random write, with 0.85mm thickness and 7% power efficiency making up the rest.
Sequential and random split along how you actually use the device. Sequential speed is the number you see moving one large file wholesale. Launching an app, scrolling a photo library, or loading an on-device AI model into memory means reading small blocks from scattered locations, and there random performance decides. Few people move 100GB in a day, but apps launch dozens of times a day — so for perceived responsiveness, 40% on random matters far more than 2.4% on sequential.
Thickness of 0.85mm reads as trivial too, until you get to foldables. In a folding device the panel, hinge, and battery all draw from the same thickness budget, so 0.15mm off one component becomes design headroom. As this comparison of two foldables separated by 14% of screen and 14 grams shows, foldable spec differences generally come out of exactly this kind of millimetre-level allocation.
Convert to package volume and the generational gap gets clearer. UFS 4.0 at 11 × 13 × 1.0mm is 143.0mm³; UFS 5.0 at 7.5 × 13 × 0.9mm is 87.8mm³. That works out to 38.6% smaller. The same 1TB now occupies under two-thirds the volume, and the freed space goes back to battery capacity or thermal structure. Storage generation changes are not only a matter of the speed table.
What to check on the spec sheet
- Whether the product page states a UFS version at all — within one model, capacity options can differ.
- Do not compare sequential speed alone. Where random read and write figures are published, those track perceived speed more closely.
- If you expect heavy on-device AI use, look at random read performance and free storage headroom together.
- UFS 5.0 enters mass production in the fourth quarter of 2026. Nothing on sale today contains it.
If you are choosing between UFS 4.0 and 4.1, the 2.4% sequential gap is not much of a basis for a decision. The substantive difference is random performance and thickness, and neither tends to appear on a finished product's spec sheet. Waiting for a device with UFS 5.0, on the other hand, has a clear rationale — 2.5× sequential speed and 40%-plus power efficiency is the kind of margin an integer-digit generation bump should deliver. But mass production starts in the fourth quarter, and shipping devices come later still. If you need a device now, the cost of waiting is the larger one.
In a UFS generation label, the decimal digit changes random performance and thickness; the integer digit changes sequential speed.