The applet at the bottom of this page -- assuming that you have a Java-enabled browser -- simulates the CPU and memory of a model computer called "xComputer." The applet lets you write assembly language programs for this computer and see how the computer executes them. The applet was written by David Eck for use with his introductory computer science textbook The Most Complex Machine. However, it can also be used on its own.
The applet below is set up to load some sample programs. These programs contain some basic instructions for using the applet. Select a program from the pop-up menu at the top of the screen. Read the comments in the program. Then click on the "Translate" button to translate the program into machine language and load it into the computer's memory. You will then be able to run the program or to step through it one step at a time. The sample programs are also available as plain text files: [1], [2], [3], [4].
This is a rather technical applet, and you will probably need to read the documentation to understand it. Documentation is available on the xComputer Info page.
For a list of other applets and for lab worksheets that use the applets, see the index page.