iPhone 7 storage tests show higher-end models are significantly faster than the 32GB version

If the advent of SSDs over the past eight years has taught us anything, it’s that storage performance matters. One of the best ways to breathe new life into an old rig is to drop an SSD in it. This truism holds true for phones as well, and we’ve seen multiple vendors make strides over the last few years to improve read and write speeds. New data on Apple’s iPhone 7 suggests that Apple cut some corners in this department.

I haven’t seen this covered before, and a quick check of various sites suggests why — the vast majority of iPhone reviews have been conducted on models with 128-256GB of storage, not the 32GB variant. Now, it’s a well-known fact that larger SSDs tend to also be faster SSDs, but we haven’t seen this tested much in smartphones. According to Unbox Therapy’s Lew Hilsenteger, there’s an up to 8x speed difference between the 32GB and 256GB Apple iPhone 7 in speed tests.

Now, this is a fairly ugly showing for the iPhone 7 32GB, but dedicated storage tests aren’t always the best way to check how fast a device really is. Much like RAM bandwidth tests, storage benchmarks don’t necessarily cleanly correspond to how fast a device is in the real world — a large difference in sequential read/write speeds might only translate to a small impact on boot time or even application load times. Desktop applications tend to be more latency sensitive than bandwidth sensitive in any case. That’s what makes Hilsenteger’s follow-up test interesting (the full video is embedded below, jump to 2:38 for the relevant portion).

Both iPhones appear to be hooked to the same USB port and Hilsenteger performs the same action on each — he syncs a 4.2GB copy of Star Wars: A New Hope to both iPhones and measures how long it took to do it. The iPhone 7 256GB finishes the copy in 2 minutes, 34 seconds. The iPhone 7 32GB needs 3 minutes, 40 seconds for the same job. That means it takes the iPhone 7 32GB about 1.43x as long to copy a 4.2GB file as the iPhone 7 256GB — and that’s not a trivial difference.

GSMArena actually hit this topic in early October, but the report doesn’t seem to have made much of a splash. According to their results, read speeds between the 32GB and 128GB models of iPhone 7 are nearly identical, but the write performance was similarly low. Their file copy tests also showed a much larger gap between the iPhone 7 128GB and the iPhone 7 32GB, though I’m not sure why (in their tests, the iPhone 7 32GB was nearly 3x slower, though the copy only took 52 seconds).

Why larger SSDs are faster SSDs

We can hazard a pretty good guess as to why Apple’s iPhone 7 32GB is so much slower than the other variants, though its not one 32GB owners will like very much. Here’s a generic SSD block diagram to explain the problem:

Note that each pair of NAND chips is connected to a channel. These channels are accessed in parallel — the more channels a device supports, the more parallel it is, and the more parallel it is (broadly speaking), the faster it is. But — and this is key — the more NAND chips you have inside a device, the more expensive it is. Imagine, for a moment, that Apple only sold a 32GB and a 256GB iPhone 7, and that both devices followed the pattern in the image above.

If Apple wanted its 32GB and 256GB devices to have identical performance, it would use an array of 16x2GB chips for the 32GB iPhone and 16x16GB chips for the 256GB iPhone. Since it has to pay for each and every chip, however, that’s not an appealing solution. Alternatively, Apple could buy 2x16GB chips for the iPhone 7 32GB and 16x16GB chips for the iPhone 7 256GB. Since the lower-end phone only has 1-2 channels, its storage will be much slower than the 256GB chip with all eight channels populated — but it’ll also save Apple more money than buying the smaller ICs.

There’s probably a practical aspect to this as well. Apple is betting it can get away with slower transfer times on the less expensive hardware because owners with just 32GB of space aren’t going to spend very much time copying data back and forth anyway. And given that file copy times still seem to be on-par with the iPhone 6s (according to GSMArena), the company probably thought most people wouldn’t notice. Still, it’s a bit shady of Apple to sabotage write performance just to pocket a few extra dollars. The company may have finally moved off its 16GB capacity, but it’s still going to gouge you if you want decent write performance.