Unresolved iMac performance issue after multiple attempts with Apple support

That base model 2019 21.5" iMac came with a really slow inferior HDD instead of an SSD.

I see two options in your future:

1) Run that 2019 21.5" iMac from an external SSD.

Use an external SSD as your startup disk … - Apple Community

2) Replace that 2019 21.5" iMac with a new iMac or new Mac mini and external display.

Mac - Which Mac is best for me? - Apple

Your iMac was the slowest iMac that Apple offered at the time of purchase: 8 GB RAM, 5400 rpm drive, i3 CPU.

However, it appears that your drive is failing based on its read and write speed:

Write speed: 16 MB/s

Read speed: 20 MB/s

It would be prohibitive costly to replace the failing drive with a modern solid state drive. However, you can get an external SSD from OWC (MacSales.com), clone your internal drive to it and boot and run from it.

You could increase your read and write speed by 10X depending on the external SSD you purchase.

I recommend that you contact OWC's Customer Support and see which of their several offerings would best fit your iMac model, work requirements and budget.

Then when you replace your iMac with a new Mac you can take the external with you for external storage.

If you decide to go either the recommendations of den.thed and get a new Mac consider this: a 10 Core Mac Mini M4 with 16 GB RAM and 1 TB SSD ($999 + tax) with a 27" LG 4k monitor ($250 + tax from Amazon.com)  is $1249 + tax which is $560 less than a similarly configured new 24" iMac ($1799 + tax)  re 07/2025.   

Your tag line says that you have a 21.5" iMac that is running macOS 14.7 (Sonoma). MacTracker indicates that the only 21.5" iMac that is capable of running Sonoma is the 2019 one.

The most likely causes of bad performance for those late-era Macs:

• Slow startup drives
• Having a bunch of software installed that is dragging down the Mac
• Hardware failure

Most of the 21.5" iMacs from that year shipped with

• Slow 1 TB 5400rpm mechanical hard drives, or
• Slow 1 TB Fusion Drives that combined a slow mechanical drive with an inadequate amount of SSD space.

If this is the only issue, it might be possible to remedy it by getting an external SSD, and using the external SSD as your startup drive.

Please download and run Etrecheck.  The free version is sufficient.

Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and after clicking on the Reply button use the Additional Text button to paste the report in your reply.

Check Etrecheck's Privacy settings and make sure the checkbox for full disk access before running:

Then we can examine the report and see if we can determine what might be the cause of the problem. No guarantees.

Emmett_1944 wrote:

If I can just ask a question to anyone. When I was researching into buying an M4 iMac some people suggested that because Apple SSD is so expensive to upgrade it was better to get the least amount of internal SSD and then buy an external SSD which was much cheaper. But then I watched this video where the person explained that you have to consider not just how much storage an external SSD can hold but also how fast it can communicate with your computer. For example a 2TB Sandisk external SSD was only $146 but the maximum speed it ran at was 1050 MB per second and in real life it would often be slower.

The interface does affect the maximum transfer speed. E.g.,

USB 3.0 runs at up to 5 Gbps (625 MB/s). You'd normally use a USB 3.0 enclosure for a SATA SSD and one of the faster enclosures for a NVMe one.

USB 3.1 Gen 2 runs at up to 10 Gbps (1250 MB/s).

USB 3.2 Gen 2x2 runs at up to 20 Gbps (2500 MB/s). Macs don't support it.

Thunderbolt 3 runs at up to 40 Gbps (5000 MB/s).

These are maximum transfer rates BEFORE overhead.

On the other hand, a mechanical hard drive will have a transfer rate of 100 – 150 MB/s, tops. And the transfer rate isn't everything. When the computer is jumping around rapidly from one place to another on the drive, something that happens a LOT during startup and during application launches, a SSD will incur MUCH shorter penalties than a mechanical hard drive that has to physically move read/write heads and wait for data to spin into place.

He said Mac's internal SSD ran at 3000 - 6000 MB per second. So if romano548 ran his entire computer from an external SSD won't that make his computer very slow, which is the problem he is trying to fix?

The point is that he has a slow mechanical hard drive now – and even worse, one that is failing. Once mechanical hard drives start to fail, trying to run off of them quickly becomes excruciatingly slow, as the computer gets hung up on the bad spots frequently, and at seemingly random times.

If he had an internal SSD now, and it was in working order, then "wouldn't an external SSD be slower?" would be a relevant question. But he doesn't.

My question would be whether he can run off an external SSD without interference from the failing internal HDD – or if he is going to be forced to have a repair shop replace that internal HDD no matter what.

Servant of Cats summed it up perfectly.

A hard disk drive that is operating in a state of failure, as that one appears to be, can be difficult to conclusively diagnose. One characteristic of that failure is poor performance. You can certainly buy an external drive (preferably, an external solid state drive) and use it as the Mac's boot device. That would be the least expensive solution toward keeping that Mac in service. If and when you decide to retire that Mac you could still use that external drive repurposed as a Time Machine backup, or for general storage. So, it wouldn't be a waste of money, and you could defer purchasing a new Mac as a replacement for some time.

In either case let us know how you would like to proceed.

+1 on the EtreCheck report. We have no idea what is going on with your computer without it. A Hard Drive issue will be confirmed, processor hangs will be identified, and processes that are running on startup that may be causing a conflict. All will cause poor performance.

Post the etrecheck report as requested above by Old Toad.

That will give us actual information we can use to make informed suggestions to try and solve your problem.

Emmett_1944 wrote:

If I can just ask a question to anyone. When I was researching into buying an M4 iMac some people suggested that because Apple SSD is so expensive to upgrade it was better to get the least amount of internal SSD and then buy an external SSD which was much cheaper. But then I watched this video where the person explained that you have to consider not just how much storage an external SSD can hold but also how fast it can communicate with your computer. For example a 2TB Sandisk external SSD was only $146 but the maximum speed it ran at was 1050 MB per second and in real life it would often be slower. He said Mac's internal SSD ran at 3000 - 6000 MB per second. So if romano548 ran his entire computer from an external SSD won't that make his computer very slow, which is the problem he is trying to fix? Also don't you have to consider the speed of the cable and ports that are being used?

We are only suggesting to run the 21.5" 2019 iMac from the external SSD.

Not a newer Silicon Mac that has a blazing fast internal SSD.

If you have a later Silicon Mac with a smaller SSD, that is starting to run low on free space..?

It would be best to continue running that Silicone Mac from the blazing fast internal SSD.

Then move your larger Photos, Music or Movie Library to an external SSD to make room.

Move your Photos library to save space on your Mac - Apple Support

Change where your music files are stored on Mac - Apple Support

Move your iMovie for Mac library - Apple Support

Emmett_1944 wrote:

I don't actually have this issue. I am just trying to learn how my computer works.

I will endeavor to be brief because I don't want to disrespect the author's original concerns, nor do I want to intrude upon any of the helpful responses others provided.

The hard disk is worn out, that much is certain, but we are discussing a Mac that was very much a low end, basic model minimally configured to perform the most basic tasks. There was no cheaper option at the time. It is my opinion that Mac has served that purpose, and has reached the end of its expected economic life.

Even adding a Microsoft product such as Word or Excel will impose processing demands such a modestly configured Mac will have difficulty with, resulting in its limitations becoming revealed.

As I wrote earlier... you get what you pay for.

Regarding that comment: It's easy to spend other people's money, but in this particular case I would invest in a fast external SSD from a reputable manufacturer (meaning, OWC) that will obviate the effects of the internal drive failures. When the OP wishes to replace that Mac, the SSD will continue to have value in its replacement's Time Machine backup, or for general purpose external storage. His or her existing modestly configured iMac will continue to function as well as it ever did (better, in fact) while the SSD remains a useful investment.

That's a 2019 iMac. I wouldn't sink any money into it. It's time for a new Mac.

Emmett_1944 wrote:

I heard about virtual RAM where if your computer's RAM is over burdened and you have extra room on your SSD/hard drive your computer will use the extra space as sort of "extra" RAM. Would romano548s computer not do this because it is from 2019?

Macs have had support for virtual memory since the days of System 7.

Mac OS X 10.0 (which ran on PowerPC-based Macs) introduced Unix-style memory management where each process runs in a separate address space, so that a misbehaving application cannot take down the system.

However, when you use virtual memory, it makes your computer run slower. RAM is much, much faster than a mechanical hard drive or a SSD. On romano548's computer, when it gets overloaded and uses virtual memory, that would involve swapping things out to "compressed RAM" or to the slow, failing mechanical hard drive. Any time the Mac has to deal with a failing hard drive, whether for virtual memory purposes or not, would be another chance for failures to cause huge, unexpected delays.

I can answer that question, which can be broadly summed up as "you get what you pay for."

An external SSD can certainly operate at a speed indistinguishable from the Mac's internal storage, but you're simply not going to find one of them for $146. It's going to cost at least twice that much.

If you don't know where to start, start here: https://eshop.macsales.com/shop/external-storage/ssd

It would try to access things on the startup drive -which could be an external drive. However, a failing hard drive, even one that had been “ejected” - might generate hardware interrupts related to its failure. (Or so it seems to me based on what I saw on my own Late 2009 iMac). The processing of those interrupts could interfere with what the computer was trying to do, even if it was running off an external drive.

Hi romano548. Some people have suggested you get a new computer. I am no computer expert but I purchased an M4 iMac with 1TB of storage and 32 GB of memory. Since the iMac has wifi 6E, I got a 6E router and upgraded our internet service to 1 Gigabit per second. I have only had it about 3 months but am very satisfied. The only problem I ran into was one day the trackpad wirelessly disconnected from the computer and I had no idea what to do because I couldn't control the computer without the trackpad. I called AppleCare and in 1/2 hour it was up and running again. Otherwise no problems. I highly recommend AppleCare if you are not computer savvy.

I have also owned a G3 iMac and a G4 iMac. On the G4 the hard drive conked out after about 3 months. I called AppleCare, brought it back to the store, and they installed a new hard drive. The computer then functioned for another 12 years without a hiccup. I can't speak for everyone but that is my experience.