How to improve performance on aging iMac (21.5 mid 2010)

Hello!

Based on your stated use of the iMac:

I have a very basic configuration, nothing out of the ordinary. I use mostly my computer for web browsing, office work, photos storage and editing.

An external SSD, even on your older iMac, WILL improve performance!

As Allan Jones said, your iMac only has USB 2.0 ports, and while an external SSD connected through these ports will still dramatically help performance due to the low seek and latency time of an SSD, you can have even better performance by using a FireWire 800 external SSD. Data transfer rates will be approximately the same as your internal disk, but as I mentioned earlier, you'll substantially improve the performance of app launch and load times due to the low seek and latency time of an SSD, which USB 2 can support for basic tasks. This means app launch, opening documents, and browsing files will all happen quicker. I run an iMac (27-inch, Late 2009) with an external USB SSD, and it makes a HUGE difference when compared to the internal hard disk, which is still reported as being healthy. System apps launch in just a "bounce" or two on the dock, and navigating within macOS is snappy.

If you choose to go the FireWire route, since FireWire 800 is an older technology, your only choice for a drive now is the OWC Mercury On-The-Go Pro SSD - OWC. You'll also need an OWC Power Adapter for Mercury On-The-Go - OWC.

However, the selection of FireWire SSDs can be pricey for the older technology. If you do not often transfer large amounts of data (5GB+) to your startup disk, and simply use your iMac for light tasks (web-browsing, office work, and light photo work), a USB SSD will work just fine. My old 2009 iMac is simply used for web-browsing, and a USB SSD is perfect for this application. Plus, you can get larger capacities for less in a USB SSD. For example, a Crucial X8 1TB Portable SSD - Crucial would be more than capable for your older iMac. You may also benefit from the upgrade of 500 GB to 1 TB since you stated you only have 30 GB free.

Regardless, if you go this route, below are the external SSD setup steps for your older model.

Connect & Erase

To start, connect your external SSD to a USB port on your Mac. Next, you need to erase and reformat your external SSD. Open Disk Utility (located in Applications > Utilities), and within Disk Utility, select View > Show All Devices. Select the external SSD entry at the top of the list (its name will also end in "Media").

Click Erase, and make sure the name, format, and scheme are as follows:

• Name: Macintosh HD
• Format: Mac OS Extended (Journaled)
• Scheme: GUID Partition Map

Click erase. After a few moments, you should see a new Macintosh HD volume on your external SSD. 

Install macOS

After erasing, you can install macOS on your external SSD. Make sure to download the latest compatible version of macOS for your Mac, macOS High Sierra: How to download macOS - Apple Support.

When the installer opens and you're asked to choose where to install, click Show All Disks, then select the new external SSD before continuing the install.

When your Mac restarts to the external SSD, follow the prompts in Setup Assistant. When asked how you want to transfer your information, select the option to transfer from a Mac, Time Machine backup, or startup disk. Then click Continue. Select your Time Machine backup or internal hard disk, then click Continue. Continue to follow the steps to restore. Large transfers might need several hours to complete.  

After Migration

After Migration, change your startup disk to set the external SSD as the default startup disk.

1. On your Mac, choose Apple menu > System Preferences, then click Startup Disk.
2. If the lock at the bottom left is locked, click it to unlock the preference pane.
3. Click the icon of the disk you want to use, then click Restart.

Additionally, after Migration, you may need to configure certain settings again, such as Time Machine.

About the internal disk

After a successful setup and Migration to the external SSD, you can erase* the internal disk. Open Disk Utility (located in Applications > Utilities), and within Disk Utility, select View > Show All Devices. Select the top-entry, click Erase, and make sure the format and scheme are as follows:

• Format: Mac OS Extended (Journaled)
• Scheme: GUID Partition Map

Click Erase. After a few moments, you should see a new, empty volume on your internal disk. 

*- If you plan to leave the internal disk as-is with macOS on it, exclude the internal disk from Spotlight indexing: Change Spotlight preferences on Mac - Apple Support. Additionally, rename the internal disk to a name other than Macintosh HD.

Jack

you could go to OWC’s website and look into swapping out the HDD in favour of an SSD. just have a look for the HDD self install videos to see if that is something you can accomplish. you could farm it out, but it may not be worth the investment for such an old iMac.

so if you feel that is out of your skill set, the other option is that you could buy an external SSD and use that to run macOS from. and from a cost standpoint, it is much more cost effective than having an iMac's internal drive replaced. please see this informative user tip: Use an external SSD as your startup disk with your iMac or Mac mini - User Tip

⚠️ The external USB SSD boot volume is not a viable option for any iMac older than 2012.

The problem is your iMac has only USB-2 ports. USB can do no faster than 480MB/sec transfer rates. Your current internal drive is up to 6x faster, so an external boot drive would drop your performance from "glacial" to "still life."

USB 3 ports began in 2012. Older USB 3 iMacs with aging mech hard drives can benefit greatly from the external boot SSD. Not yours.

You can do an internal SSD but the drive is hard or access, requires significant disassembly, and is best left to a pro who will charge you far more in labor alone than the computer is worth today.

At this point, the best action—outside of buying newer—is to see if we can make what you have today work better.

As it is highly likely your old, tired internal drive is the root issue, adding RAM would do nothing. 30GB of 500 free is a bit on the tight side; try to get its load to under 90 percent (under ~450GB).

Chrome is a huge issue with geriatric, less-capable Macs. It is a massive resource hog and your have few resources to spare.

Are you running any anti-virus software? Any so-called "cleaning" apps? Any VPN's? All will slow and destabilize your computer.

If you wish a more targeted and detailed analysis in this setting where we cannot see, touch , not remotely access your computer, please post a system config snapshot. Fortunately there is a safe, secure way to do that without our playing a protracted game of "20 Questions" that could go on for days.

We can quickly and within the confines of these forums help you determine what issues are at play if you use EtreCheck Pro, available here:

https://etrecheck.com/index

The free version will do nicely for this purpose, although the app is worthy of our financial support.

We can see hard data about drive performance, software issues, and RAM usage. Etrecheck is the development of a long-serving and trusted contributor here expressly for displaying information in these forums to help us help you. It will not reveal any personal or secure information.

Posting the report is the hardest part. Please see this excellent User Tip for instructions of posting a long report into a reply to your own thread:

How to use the Add Text Feature When Post… - Apple Community

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Download and run Etrecheck.  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 use the Additional Text button to paste the report in your reply.

Then we can evaluate the report to see if we can determine the cause of the problem.

Henry74 wrote:

I prefer using Safari but sometime it's really slow and buggy where Chrome and Firefox work much better, why?

Because Safari for High Sierra hasn't been updated but Chrome and Firefox have.

Have you considered replacing it with a more current iMac, the new machines all come with SSD's and have the ability to run current versions of Mac OS. You may also be able to find an Apple refurbished machine on Apple's web site which can save hundreds of $ and are virtually identical to a new Mac. IMHO, rather than spending money on a 13 year old computer invest in newer technology.

It can be recycled, Apple will do that for you for free. Also, did you know Apple will finance your computer purchase interest free for 1 year?