I wasn't going to get a new external drive until I tried to boot El Capitan from the same OWC drive that I used to boot Snow Leopard. It's prohibitively slow, taking about five minutes just to load, and then very sluggish in the Finder and partially functional.

Much reading on the internet has informed me that USB 3 is where it's at now. Unfortunately, I just bought a refurb 2011 iMac that doesn't have USB 3. It has USB 2, Firewire 800, and Thunderbolt 1. It does have an optical drive.

An external drive turns out be quite important. I clone the drive with SuperDuper, then do incremental backups. Much troubleshooting required me to boot from an external drive, which worked okay on my old Dual Core imac and 10.6, okay enough to get the job done.

So now I'm puzzled about which ports I should pay attention to, what drive to get, and why my current OWC drive can't cut the mustard. I assume this is a Firewire 800 port on my drive which at one time I must have considered fast. I'm not sure what the smaller port is. Nor do I recall when I bought it. It's an OWC drive with clear plastic. It says WD Scorpio Blue, 250 GB.

I don't need a large drive, but I need something with more speed.

Thunderbolt is the fastest connection of those that you have. As to the WD drive, do you know its rotational speed? You'll want 7200 rpm. If it's 5400, that will noticeably slow data transfer. Why not phone OWC and ask their advice?

You can read about the differences between versions of Thunderbolt here, Note that Thunderbolt 1, although the slowest of them, is still way faster than FW 800.

Thunderbolt drives are expensive.

True, but you get what you pay for. As for me, I find them worth the price of admission. And, of course, I'm fine with spending your money.

You indicated your priority is speed and speed is directly proportional to cost. Ie. the faster it is the more it costs and vice- versa.

Personally I was going to suggest an OWC Envoy Pro EX with an Apple Thunderbolt 3 (USB C) to Thunderbolt adaptor which should be close to rivaling the speed of your internal drive.

I talked to a guy at OWC last night. He said I could use a Thunderbolt (1 or 2) to USB 3 adapter on a Mercury on the Go portable drive. But I found only one by Kantek with mixed reviews at best. That kind of connection never caught on. I'm not sure it works.

OWC has some big price drops on Thunderbolt drives: Buffalo, LaCie, G-technology 1TB from $137 to $179. I've read negative reviews about them and have never used those brands. Could be a back to school sale or it could be they're no good. Or I could get another Mercury Firewire drive for about the same price. Or I could put a bare drive in Thunderbolt enclosure.

According to Aja System Test Lite, I'm getting 172 MB/s on my current OWC Firewire drive. Seems a lot slower than that.

The external connection you have you will always be limited by the slowest element in the system.

• Firewire 800 is , of course rated at 800 Mb/s (0.1 GB/s)
• According to design standards USB 3.0 can theoretically deliver 625 MB/s (0.63 GB/s) but you will never see that in actual data transfer because of the protocol overhead.
• Thunderbolt 1 clocks in at 10 GB/s (74.5 Gb/s)
• SATA (the drive in the enclosure uses a SATA connection is typically rated at 3.0 or 6 Gb/s (0.4 to 0.61 GB/s) According to OWC the Mercury On The Go enclosure is rated at 219 MB/s (0.22 GB/s).
• A 7200 RPM drive will have significantly less lag time then a 5400 RPM drive and will most definitely feel faster and more responsive which is most noticeable when working with small files but makes little real difference with large files or I/O intensive tasks. An SSD has virtually NO lag time and boot files are numerous but small which is why SSDs boot so much faster.

With your present drive/enclosure the speed limit is not determined by the connection to your computer but by the speed of the SATA interface in the enclosure.

The combination you suggested is interesting, with the Thunderbolt 3 to 2 adapter, if it works. With the drive, that's over $300. I was hoping for something closer to 175 or under.

Just a thought here...

Since you apparently intend to use your external for your clone, blazing speed wouldn't appear to be critical, so you might do well by returning your iMac and getting a newer one that supports USB 3...faster than FireWire 800...slower than Thunderbolt.

In total, a newer iMac plus a USB 3 external may cost no more than what you've got plus what you're contemplating.

The iMacs after 2012 have many disadvantages. I think I'll stick with what I've got. As long as I can find an external drive than can boot El Capitan I'll be satisfied with it. Doesn't have to be huge or super fast.

My long term plan is to build a PC that can be upgraded. I pick the parts. From what I can see, that is the best chance to avoid getting screwed by the tolerant, compassionate, saintly people of Silicon Valley.

Somewhat recently I bought Lacie Rugged thunderbolt2 drives. They came with an attached thunderbolt2 cable, and a USB3-Micro port with USB3 cable.

The USB3 is backward compatible with USB2, though it's noticeably slower. I use thunderbolt where possible. Getting one of these with an SSD is recommended.

One of them I bought cheaply "new open box" on eBay, removed the 1TB HDD, and installed a 512GB SSD I had removed from a prior upgrade. Love that. Big, fast, cheap.

Then I got an Open USB3 enclosure ($32?) to put my then dead 2012 macbook's 1TB SSD in. It came with a Thunderbolt 3 cable as well as a cable to USB3. Again, blazing fast, cheap, and big.

For more speed, first you want SSD all around. Then go with something that will do Thunderbolt3 and USB3 for external.

Here's the Oyen I got: https://www.amazon.com/MiniPro-USB-C-External-Aluminum-Enclosure/dp/B01N52Z26D