I’ve been using the iPhone 15 Pro for the past 1 year and only recently it got to my attention that, I gotta give the ‘revolutionary’ innovation that Apple shipped with this Pro phone, USB 3.2 Gen 2.

All started when I tuned into LTT Wan Show when Linus talking about getting the normal iPhone 16 because he don’t give a damn about the higher speed the Pro has to offer. Reason? When is the last time you really do file transfer from iPhone to PC/Mac? And if you talking about the Pros doing ProRes video, usually it’s recorded straight from iPhone to fast external SSD. And then they will just attach the storage to their workstation. It’s very normal process, and only a handful of people do connect the phone directly to PC, just to do a full backup because they ran out of storage in iCloud or just for convenience pusposes, backup and restore locally.

I came across a reddit post by Time-Explorer2000 - Backup 15 Pro via USB cable still running at USB 2.0 speed, painfully slow : r/iphone (reddit.com) and I decided to run the test myself and wrap my head around this, trying to find a reasonable explanation.

Here is my so called professional testing with no screenshot evidence. But give it some read

4 cables (3 3rd-party, 1 Apple provided cable)

  1. Thunderbolt 4 - 40Gbps
  2. USB 4.0 - 40Gbps
  3. USB 3.2 - 10Gbps
  4. iPad USB-C Cable USB 2.0 - 480Mbps

Transfer speed control

  1. Windows PC file transfer between external SSD (SSD rated at 550MB/s | 4.4Gb/s)
  2. 5x 6GB .ISO files as transfer subject, 30GB in total. Reason: avoiding small chunks. Total 5 pass.
  3. Differentiation between MB/s, Mb/s and Gb/s
  4. Verify each negated link in USBTreeView, to make sure it’s at least on USB 3.0, USB SS & Above.

Actual test

  1. External SSD -> PC
    • Cable 1-3: 400MB/s | 3.2Gb/s +- (expected, 25% fluctuation)
    • Cable 4: 48MB/s | 390Mb/s +- (expected, USB 2.0 spec)
  2. iPhone 15 Pro -> External SSD
    • Cable 1-3: 300MB/s | 2.4Gb/s +- (expected)
    • Cable 4: 40MB/s | 320Mb/s +- (expected, USB 2.0 spec)
  3. iPhone 15 Pro -> PC
    • Cable 1-3: 100MB/s | 800Mb/s +- (above USB 2.0 spec, but way lower than USB 3.2 Gen 2)
    • Cable 4: 22MB/s | 176Mb/s +- (expected, iPhone 7, iPhone 11 around the same speed)
  4. iPhone 15 Pro -> iPad Air 9th Gen
    • Couldn’t determine accurately, but cable 1-3 are fast. Faster than from iPhone to PC
    • Cable 4, expected to be slow and it’s.

My verdict

The iPhone have capable interface, but the media transfer protocol (MTP) is technologically limited. Well at least, for what I’m about to say below.

I believe, when transferring directly from a compute device to external storage, we are referring to USB Attached SCSI Protocol (UASP), this usually is fast since there’s no overhead to be taken care of in a sense, host can read the filesystem and directly transfer. But when it comes to MTP, there’s a lot more to it (pseudo-fs), but the gist of it, maximize compatibility so any device can read. The downside, it’s going to be slower since you are accessing virtual filesystem through pseudo-fs.

Think of it as, if your device is Windows, and the NVME on iPhone 15 Pro is an APFS container, definitely your Windows can’t read directly, unless you go through MTP->pseudo-fs->APFS. They just went ahead keep it the same protocol even when you connected it to a MacBook. It just works, dont break it. This also applies when you do Wireless file transfer using iTunes/Apple Devices/iMazing/etc.

But when you do transfer from iPhone to external storage, it’s USB Mass Storage and it’s, like I mentioned above, UASP. It’s pretty much direct, and it’s fast, given that your external storage is compatible (e.g exFAT) and if the storage itself is fast enough.

End user like can’t really do anything except building a hardware interface to bridge iPhone-> UASP -> External SSD -> UASP -> PC, just to get it slightly faster by buffering the transfer from iPhone to SSD and then from SSD to PC.

Or learn C++ and introduce a new protocol 🤣

I’m no expert in this USB stuff, but this is what I understand, and how this unfold into a reasonable conclusion.

Now, I just need to find modern Android to do the same thing. USB Mass Storage becoming less common in Android since around 10 years ago, but you can still enable it. And do the comparison between MTP vs USB Mass Storage option.