Is there a way to reduce the CPU usage and reduce the amount of RAM used?

Thank you. I will try that. I honestly haven’t wrapped my brain completely around what spacing means in this program. I’m coming from Fiji and Amira where I had serially sectioned epoxy embedded animals at 1um thick sections, photographed each section and registered them in a stack. So spacing to me means the distance between slices (1um in my case) and to have the 3D slicer “spacing” in three dimensions makes me think I’m not understanding this.

Here is my hardware:
|Model Name:|iMac|
| Model Identifier:|iMac18,3|
| Processor Name:|Intel Core i7|
| Processor Speed:|4.2 GHz|
| Number of Processors:|1|
| Total Number of Cores:|4|
| L2 Cache (per Core):|256 KB|
| L3 Cache:|8 MB|
| Memory:|64 GB|