how does 1 tb storage on a 2017 imac compare with 512GB SSD storage

Welcome!

21.5 or 27-inch? That makes a massive difference in your upgrade options. RAM is easy to upgrade in the 27-inch but terribly difficult in the 21.5-inch, so much so I cannot recommend upgrading RAM in any 21.5-inch iMac made after 2011.

Much of what we can recommend requires our knowing what storage option you now have:

• The 27-inch 2017 iMac base model had a 1TB Fusion (hybrid) drive system (fast).
• The 21.5-inch 2017 base model had a 1TB mechanical hard drive (slow).

Larger Fusion systems and solid-state drives were factory options for both.

Also do About this Mac..' and look for your sub-model. Example:

If yours is a 21.5-inch sub-model and DOES NOT include "4K" in the sub-model, you have the crippled educational/institutional model with a slow laptop processor and I cannot recommend any upgrade outside of an external USB3 SSD.

While "About" is open, click the "Storage" tab and tell us what kind of drive that shows:

So please tell us more so we can give you a much more specific reply.

Thanks!

An ssd gives better performance. The storage remains the same, so 512 on a ssd is 512, its nothing more then that and a terabyte is more storage. But a spinning harddrive has lesser performance due to speed. If you want to have 1tb I strongly recommend to go with a SSD with 1 TB storage

8Gb memory in total? 16 is better and meets more modern standards then 8