I recently purchased an iMac Retina 5K, 27-inch display, with 1TB Fusion Drive, which came with 8 GB memory as standard.
http://www.apple.com/uk/shop/buy-mac/imac?product=MK472B/A&step=config#
However, I found it would slow down considerably a few minutes after booting / rebooting, I thought the Fusion Drive would compensate somewhat for the 8GB memory.
After performing several tests, it came down to Google Chrome hogging memory, and not really releasing memory when closed, even though Activity Monitor showed it had.
Chrome is my secondary Browser, Firefox being my main Browser, but this was also affected, including many other programmes !
I had used Migration Assistant, to transfer data from my other main iMac, a slightly older model.
..... So a version of Chrome with attendant slowness !!
Both OSX El Capitan 10.11.6
This had also started to slow, and I had added extra memory, which cured this.
Anyway, after a bit of web searching, I came across the solution.
This basically involved deleting the Chrome Default settings, Chrome then added new settings upon next booting up.
I also quite drastically pruned several Extensions, not all enabled, but presumably loading anyway !
When I pressed the Space Bar to scroll Page Down, the first time I did this after Chrome had opened, the iMac(s) would seize up, Spinning Ball.... for perhaps 10 seconds, very annoying.
The 27" now zooms along, with no memory conflicts nor slowing down at all, usually reporting 5GB memory available most of the time.
Space Bar page down is now also immediate.
So, if your iMac is showing the same symptoms, try this....
This is what I did:
Step 1
Click "Go" on the main menu bar at the top of your Mac desktop.
Step 2
Select "Go To Folder" from the drop-down menu, then double-click the "Library" folder in the new window.
Step 3
Double-click the "Application Support" folder, then double-click the "Chrome" folder. The Default folder is one of the folders in the Chrome folder.
Step 4
Click on the name of the Default folder, then press the "Enter/Return" key and rename the folder "Backup Default." Don't close the window.
Step 5
Launch Google Chrome. After you start surfing the Internet, a new "Default" folder is created automatically in the Chrome folder.
Step 6
Double-click on the newly named "Backup Default" folder in the Chrome folder window to open it, then select the "Bookmarks.bak" file.
Step 7
Click "Edit" on the menu bar at the top of the desktop, then select "Copy" from the drop-down menu. Double-click the new "Default" folder to open it.
Step 8
Click "Edit" again from the menu bar, then select "Paste" from the drop-down menu. The "Bookmarks.bak" is transferred to your new Chrome user profile so your old Chrome bookmarks appear on the browser. Surf the Internet as usual.
The only thing I seem to have lost is the History, and my start-up pages, though all bookmarks have been retained.
All startup pages now bookmarked as a whole, just in case I need to perform this again...
I am also duplicating the Chrome Folder within Application Support on a regular basis, plus the default folder contained within, should I need to revert back to a speedy, working setup.
(This does work I've tried it)
