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I'd like to be able to test memory thoroughly in Macs (2015 and later, for older Macs I use Apple ASD tests). I tried Memtest but it won't boot from a thumbdrive for some reason.

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    Its silly this question is closed as its one of the top hits on google when searching for "test memory on mac". I could not get Passmark's MemTest86 to boot so what did work was Memtest86+ and download the "Linux ISO w/ Grub (64bits)", unzip the ISO file then use Etcher to burn the ISO file onto your USB thumb drive, reboot and hold down OPTION, choose "EFI Boot" entry. See this link. The Linux Grub boot loader was the key to making it work on the Mac Dec 15, 2022 at 1:40
  • Your instructions worked great for me, thanks! Agree on not understandable why this question is closed.
    – blitter
    Apr 1, 2023 at 14:49

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Use Apple Diagnostics. Its an Apple-approved method of checking your memory and other hardware parts of your Mac. You can restart your Mac, then hold down D as soon as it restarts. If you did it correctly, your computer will either boot into Apple Diagnostics or Apple Hardware Test, depending on the age of your machine. Then just follow the prompts.

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    HI jmhj, thanks for your answer. As I said I'm looking to a thorough test (which usually take more than 1 hour). Apple diagnostics just does a quick 2-3 minute test if I'm right. Oct 3, 2019 at 3:30
  • that's fine. If you test drive it, let me know how long it takes.
    – Natsfan
    Oct 3, 2019 at 3:34
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You probably didn't set up Memtest properly. Here is how:

Check Your Memory Using MemTest86

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If you want to learn more about any problems Apple’s diagnostics detected, or you want to run another test for peace of mind, MemTest86 is one of the best tools for the job. There are a few memory testing tools that use similar names, but MemTest86 is still regularly maintained and updated.

To test your machine, you’re going to need to make a bootable USB drive from which to run the test. The first step is to find a suitable USB drive and make sure there are no important files on there since the whole drive will be erased. Insert the USB drive into a free port.

Now download the free drive creation tool Etcher, mount the DMG, and install it to your Applications folder. Head to the MemTest86 Downloads page and grab the Image for creating bootable USB Drive under Linux/Mac Downloads.

Once MemTest86 has downloaded, extract the archive and launch Etcher. Click Select image, navigate to the extracted archive you previously downloaded, and choose the memtest-usb.img file. Now click Select drive and choose the USB drive you want to use. When you’re ready, click Flash! and wait for the process to complete.

Create Bootable USB with Etcher

Next, shut down the Mac you want to test and insert the USB drive you just created. Press and hold the Option key and power on your Mac. When prompted, select the external drive you created (it may show up as EFI Boot) by clicking the arrow to boot into MemTest. Don’t select Macintosh HD, since this is your internal drive.

Wait for MemTest86 to initialize. Testing should begin after a short pause, but if it doesn’t, select Config then Start Test. Allow time for the test to complete; it took around 40 minutes on our test machine. In the end, you’ll be given a summary, and an option to save a report to the USB drive in HTML format.

MemTest86 Running on a MacBook Air

Save the report if you find anything unusual and use it to seek help from an Apple technician or Apple Support.

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    Thanks for that, I'll try it asap. I guess you need to burn the USB stick in a Mac and not in Windows, right? I'd be a bit easier for me to do it in Windows. Oct 3, 2019 at 3:34
  • Correct, Mac uses different formats for bootables Oct 4, 2019 at 12:25
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    Fantastic, important clarification. Oct 5, 2019 at 16:31
  • See this link where I wrote up the proper instructions using a different tool Memtest86+. The Linux Grub boot loader was the key to making it work on the Mac Dec 15, 2022 at 1:41
  • Worth adding that MemTest86 and Memtest86+ are two totally different programs by different vendors. Memtest86+ is open source and free, while MemTest86 seems to be a commercial effort. Nothing wrong with that, just clearing up potential confusion.
    – blitter
    Apr 1, 2023 at 14:53

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