Do you ever see circles displayed as lines in Autocad?

Does the mouse freeze in Autocad?

It's just a case of typing the short cut key RE. This will force a regen of what, in programming language, is a display list. ie. A short list of data about objects that appear on screen. 

As you scroll or pan with a mouse, the views you see are created by the faster speed available from the shorter display list. When the list is empty the mouse stops. A regen command will go back to the full data base and top up the display list again.

You might see facted circles (typically octagon shaped instead of circular). CAD can work faster with these faceted circles or arcs. So once again RE for regen will display them correctly.

There is a variable called viewres which can lesson the impact of faceting, though plotting is never affected

The value of viewres in many older drawings you may find was set to 100. Typical today's default value is 1000 but it's highest available value is 20000. Probably not nearly high enough to slow today's computers. Though that does still depend on the size of a CAD drawing.