USB 3 vs Thunderbolt

Posted on by Larry

I’ve gotten a lot of questions recently on USB 3 vs. Thunderbolt, so I wanted to share what I’ve learned.  (By the way, I updated this to provide clarity on USB 3 speeds.)

Thunderbolt and USB 3 are both protocols for transferring data from one place to another. The easiest way to imagine that these are “pipes” that carry water. USB 3 is a big pipe. Thunderbolt is an even bigger pipe. The bigger the pipe, the more data it can transfer at one time.

Thunderbolt Is A Really Big Pipe

USB 3 has a top speed of 5 Gbps, which equals about 600 MB/second.  Thunderbolt has a top speed of 10 Gbps, which converts to 1.1 GB per second; which is about two times faster.

NOTE: Data speeds are often measured in bits per second (bps – note the lower case “b”). Hard disk speeds are generally measured in Bytes per second (Bps, note the UPPER case “B”).  To convert bps to Bps, divide bps by eight.  bps/8 – Bps.  I use Bps for all the speed measurements in this article.

Now, in order to hit those maximum speeds, you need to have a RAID containing at least five drives for USB 3 and ten drives for Thunderbolt. If your storage has fewer drives, it will still go fast, but it won’t “fill the pipe.”

NOTE: A quick way to estimate the speed of your device is to multiply the number of hard disks it contains by 100 MB/second.

USB 3 Can Have Problems

Fred offered a comment on my blog about “Configuring an iMac for Video Editing”:

I’ve been using USB 3 on the PC side for some time and the issues that Apple is having with it are not new and not Apple-exclusive. USB 3 is notoriously dicey. If you try to use a hub with it, it will become completely unreliable. Some early interface chipsets in the drives are very fussy with speeds ranging all over the map. I’ve had good luck lately with the newer stuff. The small Buffalo drive I got with both USB 3 and Thunderbolt seems to perform pretty well both ways on my Mac Mini. But my thinking is that Apple won’t have answers on the USB 3 issues for you because they aren’t specifically Apple’s issues.

Which to Pick?

Both Apple and Intel are aggressively reviewing all Thunderbolt devices – as part of their Thunderbolt Certification program – to make sure all new Thunderbolt devices meet the spec and play nicely with others. This is one of the reasons Thunderbolt storage is taking so long to come to market.

Architecturally, Thunderbolt is built for higher speeds than USB 3.0. My recommendation is use Thunderbolt for the best performance and reliability. If you need PC compatibility, use USB 3. Thunderbolt for Windows is coming soon and, when it arrives, is the best choice for maximum performance.

NOTE: As a side note, you can’t attach a Thunderbolt hard disk to a computer that doesn’t have Thunderbolt using a FireWire cable. I know because I tried, then learned from tech support that it doesn’t work that way.

As always, let me know what you think.


23 Responses to USB 3 vs Thunderbolt

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  1. Jeff Kirkland says:

    An excellent and well timed article. I unpacked my 27″ iMac on Monday and have been trying to make sense of my storage options ever since.

    The one thing I’ve found out about USB3 drives this week is that they can vary in speed, even across the same make and model. I had three Seagate GoFlex desktop drives from another project, all purchased at the same time. They range in speed from 80MB/s to 140MB/s across the three using the same interface and cable.

    I’m coming to the conclusion that the best way forward is to buy an enclosure and add my own drives so that I know exactly what’s in the box.

  2. Jason Lavish says:

    So let’s get this straight… If I have just a single drive enclosure on either USB 3.0 or Thunderbolt, my actual transfer speed will only top out at 100MB/sec? And if that is so, then what am I getting right now with my single 3G HDD enclosures running on eSATA or Firewire 800?

    • Larry says:


      Using today’s technology, the speed with which a single drive can transfer data ranges between 100 MB/second and 150 MB/second. If you are using protocols like FireWire. USB2, or iSCSI your transfer speed will be slower than that because the protocol can’t keep up with the drive. If you are using USB 3, eSATA, or Thunderbolt the protocol is fast enough to keep up with the drive.

      For example, FireWire 800 tops out around 85 MB/second, regardless of how fast your drive is going, due to limits in the FireWire protocol.


  3. Jason Lavish says:

    Okay, I think I’m getting it. LOL! So until HDDs that transfer at 500 MB/sec or 1GB/sec. are designed, we won’t be hitting that top transfer speed potential with a single drive alone, just with RAID systems.

  4. Moz says:

    Further to Jason and others comments;
    I use Crucial SSD’s for HD recording media which are promoted to run at 6G and seem to test at around 500 MB/sec in my current system without RAID.
    It seems to me were already hitting the point where I am topping out my USB 3 ports and with out a major platform change I will be backing the wrong horse for a fair while to come (as versus T’Bolt).
    With the prevelance of High def and high speed video the crunch is here already and yet the technologists seem to have discarded the parralel technologies, it all seems to be convenience driven, plug and play is winning over performance already.

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