Opening a large file very fast

[tbscope]

When I load a large textfile into a richtextbox, this is very fast.
ex. richtextbox.filename = "something"

Trying to open the file with a get instruction is very slow.

I would like to know how I can open a file as fast as the richtextbox?

ps: I don't care if you explain it with c++ code.

Any help would be appreciated.
Thanks.