What is the difference between internal and external memory in computer?

It is often difficult to puzzle out what people are talking about. A lot of people think the monitor is the computer and the computer (the whole box) is the hard drive. Such a person knows that memory is important but has no idea what it is. I would guess that what you mean by "external memory" is a hard drive with USB interface. Internal means inside the box, where there is a hard drive and integrated circuits that are actually called memory. One memory IC is called BIOS and it contains the program that loads the operating system. The other memory IC is called RAM and that is the part that runs a program.