iMac keeps freezing every minute

This sounds like a failing HD. Please restart in the Recovery Partition (Command + R on startup) and open Disk Utilities and then run First Aid on the internal drive 2-4 times. If any errors appear that confirms the hunch. If no errors appear then you can try restarting in Safe Mode( Use safe mode to isolate issues with your Mac - Apple Support) and see if that helps, otherwise it will need to have to go to a local Apple Authorized Service Provider to be diagnosed.

If you get a 21" the RAM is only upgradeable by an AASP, even Apple Stores will not do it, the cost of upgrading for labor alone would make it cost prohibiitive as it requires a complete disassembly of the computer.

The advantage of a SSD is it's speed and reliability. SSD's have no moving parts whereas traditional HD have moving parts and will fail earlier on average than SSDs. While SSDs are more expensive the user experience far outweighs the cost. If you get a 21.5" with a hard drive your will be EXTREMELY disapointed as they are downgrades from machines made before 2012.

As suggested:

• • 21.5" get the largest SSD you can afford and 16 GB of RAM or more
  • 27" get the largest SSD you can afford and buy with 8 GB of RAM and then upgrade to 32GB using Crucial.com or Macsales.com RAM.

I also have a 2011 iMac, the same configuration as yours. About 5 years ago I installed a 256GB SSD and have used that as my primary drive. However, now that the computer is almost 10 years old it's time to replace it. My intention is to go with another 27" with a 512GB SSD this time.

If you are going for a 21.5", buy a minimum of 16GB of RAM and the largest SSD you can afford. The RAM on these are NOT upgradeable and the hard drives are very slow 5400 RPM drives, in short if you get a base configuration it would be a dramatic downgrade over your 2011.

First lets define what a Fusion drive is: A fusion drive is a combination of a very small SSD that is fused with software with a traditional spinning hard drive. Fusion drives are faster than just a traditional HD becuase the SSD portion is used for startup and shutdown operations. You cannot define the size of the SSD used!

If you purchase an iMac with just a SSD it is just that, a SSD all by itself. So if you can only afford a 256 GB SSD it will be fast but is limited to only 256 GB of storage. If you need additional storage then your best option is adding external HD's (we recommend the OWC Mercury Elite Pros) .

On my computer I have just a 256 GB SSD but have several large HD's attached for storing large libraries such as my movies (close to 1000), photos, and music. What tends to take up the most space on computer storage are those items. My SSD is only used for keeping Mac OS, my applications and some files I use daily. Everything else is on EHDs and has been that way for years.

Your 2011 is better in most every way than the new 21.5"ers limited to 16 GB of expensive RAM.

Restart normally.