The iPhone 18 Pro Max is the rare phone where paying more for storage can cost you speed. Independent testing indicates that the 1TB and 2TB configurations of the iPhone 18 Pro and iPhone 18 Pro Max use QLC flash memory. The cheaper 256GB and 512GB models use TLC flash, which is the faster of the two.
The difference comes down to how much data each memory cell holds. TLC stores three bits per cell. QLC stores four, which makes capacity cheaper to build but slower to write and less durable over time. The iPhone 17 Pro generation used TLC across every tier, including 1TB and 2TB. That is the part buyers should note: this is a step down from last year at the top of the range.
What the iPhone 18 Pro Max storage testing found
The numbers come from a tester called Homolab, who posted a comparison on Bilibili. Tom’s Hardware and GSMArena relayed the results in English. The test pitted a 512GB iPhone 18 Pro Max against a 1TB unit in sustained write runs.
With the drive close to empty, both behave well at first. Writes start in an SLC cache at up to roughly 3,000MB/s. On the QLC unit that drops to a TLC cache tier at 578MB/s, then falls again to 79.4MB/s once it is writing to bulk QLC storage. The slowest dips measured 25.6MB/s.
The gap widens sharply as the phone fills up. At around 60% storage used, the SLC cache on the tested unit shrank from 250GB to 58GB. In that state, sustained writes measured 396MB/s on the TLC model and 1.1MB/s on the QLC model. Random access showed a smaller but real penalty. The 1TB unit was 38% slower in 4K random reads at low queue depths, narrowing to a 12% gap under heavier load.
Two caveats matter. Only the 1TB Pro Max was put through these benchmarks. The QLC designation for the 2TB tier and for the smaller Pro is reported rather than separately measured in this test.
Does this affect how you actually use the phone?
For most people, no. Messaging, browsing, casual photography and gaming never push flash storage hard enough or long enough to drain the cache. The slowdown is a sustained-workload problem, and it surfaces in a narrower set of situations:
- Long 4K or ProRes video recording — continuous high-bitrate writes are exactly the workload that exhausts the SLC cache.
- Large file transfers — moving tens of gigabytes on or off the phone in one go.
- Full backup restores — setting up a new device from a large iCloud or computer backup.
- A phone that stays mostly full — the less free space, the smaller the cache, the sooner you hit the slow tier.
Those are also, awkwardly, the reasons someone buys a 1TB or 2TB phone in the first place. A videographer paying the largest storage premium Apple charges is the buyer most likely to run into the component that was traded down.
Apple does not list flash memory type on its spec sheets, so there is no way to tell TLC from QLC at the point of purchase. As of September 24, no Apple comment on the testing has surfaced. If your use is ordinary, the larger tiers are still fine. If you shoot long-form video for a living, the 512GB model may genuinely serve you better under load than the tier above it.
Sources: Homolab (Bilibili), via Tom’s Hardware, GSMArena
