Dec 18, 2017. This is the recommended way by Apple to test your memory using their diagnostic tool. If you have an installation disc, insert the disc, restart your Mac, press and hold the C key. Select the language for the Apple Hardware Test and click the Test button to start testing.

Most Mac users will experience years of using a Mac without any problems. But every so often, a hardware issue could surface that could significantly impact how your Mac performs.

Identifying the cause of problems — hardware or software — is the first step to fixing them. It could make a trip to an Apple Store or certified reseller easier knowing you've done all you can to identify and whenever possible, fix the problem yourself — saving you downtime and a potentially costly repair.

Built into every Mac is a way to run an Apple Hardware Test, also known as an Apple Diagnostics.

Hardware Tests are an effective way to identify the cause of a Mac performance problem, which could be CPU or GPU issue, a failing disk drive, an overloaded memory, a fan overheating, or any number of other potential faults. If you suspect it’s a hardware problem, Hardware Tests are the way to troubleshoot on Macs built before 2013. In newer models, those built after 2013, those same tests are labelled Apple Diagnostics.

How to Run Apple Diagnostics on any Mac

In some cases, a hardware problem is so severe that you won’t be able to switch your Mac back on. Thankfully, if you can run an Apple Diagnostics or Hardware Test, Apple Support suggests this is a way you can restart your Mac, even if it refuses to switch back on through other means.

Whether you are running an Apple diagnostics (on newer hardware and OS X devices) or a Mac hardware test (on older devices), Apple recommends printing their support instructions on how to run these tests. Once you’ve got the instructions in front of you, Apple recommends going through the following process to diagnose a hardware problem:

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  1. For those with iMacs or any desktop-based device: Disconnect all external drives and hardware devices, except for the keyboard, mouse, display, and speakers.
  2. Select Apple Menu > Restart.
  3. Press and hold the D key when the Mac is restarting.
  4. Apple Diagnostics will run automatically. When it is complete, it will present a list of the problems encountered.

Common Mac Hardware Issues

At this point, you can either follow on-screen instructions or contact Apple Support — arranging a Genius Bar appointment — or go to an Apple Authorized Service Provider to make repairs, to fix the problems. Make a note of any reference codes.

Some of the most common hardware error codes indicate problems with:

  • Wi-Fi — a failure of the AirPort wireless card (4AIR);
  • Hard disk and SSD (4HDD)
  • Logic board (4IRP)
  • Memory — RAM (4MEM)
  • External disk (4MHD)
  • Fans (4MOT)
  • Processor (4PRC)
  • Video/graphics card (4YDC)

Most Mac error codes suggest a failure of the component they reference, or a related component that is causing a problem with the hardware. In most cases, an Apple specialist or technician may be needed to resolve this issue.

However, before you send your poor, unhealthy Mac off to the shop, there are several fixes you could try at home, such as resetting the PRAM or SMC. This can fix some of the most common errors, including problems with the logic board and fan.

Disk Utility (built-into every OS X) is useful for fixing memory (RAM), hard disk and external drive problems, as are several third-party apps.

For those with older Macs, when you are running an OS X Hardware Test, an alert message will appear once complete with a list of the problems encountered. Again, you have the option of following on-screen instructions to restore the Mac, or re-booting the device using a startup disk, or taking the Mac to a store or Authorized Service Provider.

In any scenario involving hardware, you need to be aware that you are at risk of losing any items on your Mac that haven't been backed-up to the cloud. We recommend storing as much as you can with a cloud provider, such as Dropbox, or Apple iCloud.

Another way to improve Mac performance

What happens if you run a Mac diagnostics and it comes back with nothing? Does this mean you need to buy a new Mac? Or give up using Mac altogether, switching to another device and operating system?

An Apple Diagnostics or Hardware Test that reports a lack of problems indicates it could be a software issue. Another alternative worth exploring, especially if your Mac is overheating or slowing down, is that your storage is too full of junk, clutter, applications, and duplicate files and photos.

On average, Mac users have 62GB of data, files, apps, and images they do not need. Too many files slow down and overheat computers, making them difficult to use and causing them to crash more often.

CleanMyMac X is designed to clear up junk, clutter and get your Mac back to peak performance. With over 4 million downloads and hundreds of positive reviews, we know that CleanMyMac X has carefully removed over 11 million unnecessary apps and over 2.5 billion gigabytes of data clogging up Macs all over the world.

With two click removals, you can quickly clean loads of data, making your Mac easier to use and freeing up space for new documents, downloads and images. Once you've run a Hardware Test or Apple Diagnostics, use CleanMyMac X (it's free to try) to identify and fix any other issues that are causing your Mac to run slowly or overheat.

We hope this article was helpful and you found the answers to all your questions here. Stay tuned!

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Mac can be conveniently purchased from the Apple store and most of configuration allows you to upgrade the memory so that you don’t need to open the case and take the risk in using an incompatible memory which would cause system lockups. The only thing is the upgrade from Apple store cost a lot more money if compared to the one that it purchased from a computer store. For example, an additional 2GB of memory cost $50 at Apple Store while it only cost less than $10 if you search in Pricewatch. If you’re willing to take the risk in adding extra memory in your Mac either to save money or perhaps you have a few lying around, it is best to run a memory test to make sure that the RAM is fully compatible and won’t make your Mac unstable.

Here we suggest 3 different methods to easily run a memory test on your Mac OS X including the latest Mountain Lion 10.8.

1. Rember

Rember is actually a GUI for the popular command line memory testing tool called Memtest OS X. Instead of typing commands in terminal, you can run the test by clicking a button. You are able to test a selected amount or all of the memory, specify the number of times the tests should run and also viewing of the log. Rember includes Memtest OS X in the package so there is no need to manually download and install the memtest. Running Rember will show a table displaying the detected memory on your Mac. Select the amount of memory to test, number of loops and click the Test button to start checking the memory. When the tests is finished, Rember will show the test results.

Rember runs in Mac OS X which means that not all of the ram can be tested due to a portion of RAM being reserved for housekeeping.

Download Rember

2. Memtest86+

If your Mac has a SuperDrive, you can burn the pre-compiled bootable ISO image of the Memtest86+ and boot up the Mac with the disc. Just press and hold the C key when starting up Mac to boot from the disc. The good thing about Memtest86+ is it runs by itself without relying on the operating system, giving you a more accurate memory test result.


Download Memtest86+

3. Apple Hardware Test

This is the recommended way by Apple to test your memory using their diagnostic tool. If you have an installation disc, insert the disc, restart your Mac, press and hold the C key. Select the language for the Apple Hardware Test and click the Test button to start testing. You can also tick the “Perform extended testing” option which would perform a more thorough test that takes considerably more time to complete. On the latest Mac OS X Mountain Lion, the Apple Hardware Test is already pre-installed and it doesn’t come with an installation disc. Simply boot up, press and hold the D key to start the Apple Hardware Test.

You can also see the amount of memory installed on your Mac at the Hardware Profile tab to confirm that the memory is correctly installed and detected. There are some Apple Hardware Test images that can be downloaded for older models. Do note that the Apple Hardware Test images are machine specific meaning that you cannot use the iBook version on a Mac Mini.

Download Apple Hardware Test

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Night2 months ago

‘Closing all apps’ is an option which can be set or disabled in the Rember preferences.


I’m trying to test DRAM one bank at a time in mid-2010 Mac mini with 2 banks of 4GB Kingston DRAM each.

Mac Os Hardware Test

Rember run overnight on max cycles (255) showed when both banks were full (8GB total), there was a DRAM failure. But run overnight on max cycles (255), Rember is so slow it’s completed less than 30 cycles. I tried this twice.

Is it not possible to check one 4GB stick at a time? (Mid-2010 Mac mini standard RAM is 1GB module in each bank for total 2GB.)

Charlzm9 months ago

I have several DDR3 DIMMs I want to install, but the memory timing is not printed on them. Is there an app for Macs that can tell you what the timing is on installed DIMMs?


Rember doesn’t shut down existing programs… you do that yerself


Mac Hardware Test Cd Download Software

Rakiki1 year ago

Rember is an amazing app! In regards to the comment above:

it closes all windows because to free-up whole RAM memory for tests.
It’s understandable that you must save your work before you open any diagnostic app.

Works great on latest 2019 iMac where Memtest failed and Apple Diagnostic Tool is a JOKE



I ran this app and it closed all open windows and running apps without asking or warning me. That is bad software. Who knows what data I lost as a result, let alone time in reopening what I can remember was running. memtest does not do this.

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Ron Helgerson5 years ago

Hope this works well, thanks!


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