Yes, you've got it exactly. When running in real mode, if an interrupt arrived the processor would switch to protected mode, handle the interrupt, and return t

Yes, you've got it exactly. When running in real mode, if an interrupt arrived the processor would switch to protected mode, handle the interrupt, and return to real mode. This real->protected->real switching process was so slow on the computers of the day that it was possible to lose data, so it was necessary to write both real and protected mode interrupt handlers to grab data off the serial port. You can imagine how much fun this type of code would be to write without any debugging tools or an Internet filled with code-samples.