It&#x27;s how very early version of Unix effectively did stuff, they exceed a program, and when it exited they exceed the shel again.<p>When they introduced something like the fork&#x2F;exec model we now have they discovered cd didn&#x27;t work any more and had to write it as a built in.<p>Now, for bonus points, work out how goto worked when it wasn&#x27;t a built in.