Emulation

Apple computers can run Microsoft Windows ".exe" files (executable files) intended for Intel computers even though these machines have different architectures. This is done by running a program on the Apple that emulates (imitates) an Intel processor.

A processor's architecture is a logical description of its components and its basic operations. This says nothing about how the architecture is implemented.

The operations need not be done in electronics. They can be done with software. A program that implements a processor's architecture is the logical equivalent of an implementation in silicon. Such a program is called an emulator. Any computer can run an emulator of any kind of computer. Of course, somebody has to write the emulator, and that is difficult.

You could do a long division problem with paper and pencil. Or the same operations could be done by an electronic calculator. The steps in doing the problem are the same (mostly), but the implementation is different.

The basic flow chart of an emulator program is the machine cycle of the emulated processor. But now the steps are implemented in software, not in silicon. The emulated machine cycle involves perhaps thousands of program statements. When the emulator is running, each simulated machine cycle requires the execution of many instructions on the host processor. So emulators run much slower than the processor they are emulating.

This course uses an emulator for the MIPS architecture. Using an emulator has many advantages over using the actual hardware. The biggest advantage is that the architecture described in these notes will exactly match the architecture implemented by the emulator. You can download exactly what you need to use to follow these notes. The emulator runs on most common desktop computers; PC, Mac, or even ... MIPS.