How does vim read files?

  question, vim

It is found that notepad++ is very stuck when reading large files, but gvim can be handled smoothly.
Vim is a line editor like ed, which processes files line by line or partially?

No, vim is all loaded into memory. vim has been used to look at several g of log files and directly eat up the server memory before. Therefore, less is generally recommended to look at large files on the server side.