The Visible Virtual Machine (VVM) is a decimal based digital computer.  It reminds me of the Fiasco Computer I saw years ago as a student.  It serves to illustrate the fundamental operations of all digital computers without causing us to get lost in too many details. 

Professor Stu Westin of the University of Rhode island developed and maintains this program. I should warn you that he appreciates feedback on this package. However, he is unable to answer specific programming questions about the VVM. So, please don't E-Mail him asking for a solution to a homework assignment. He won't give it to you.

The internet home page for the Visible Virtual Machine is http://www.cba.uri.edu/Faculty/vvm/

Accessing VVM From Home or the Office

I strongly encourage you to download this software, install it on your PC and try it.  Before downloading the VVM zip file, I encourage you to create a new folder to contain all the VVM files.

You can download the Visible Virtual Machine by clicking here.   vvm502archive.exe is a self-extracting archive. You must execute this program before you can do anything else. You can do this using Run from the Task bar or by double clicking the program from Windows Explorer®. Executing vvm502archive.exe will extract the following 2 files to the directory that you specify.

Setup.Lst
Setup.exe

You must now execute the program setup.exe to actually install the VVM on your computer.

Once VVM is installed, if you followed my advice and extracted the files in vvm502archive.exe to a newly created folder, this folder can now be safely deleted.

You will find the Visible Virtual Machine under Start Programs Visible Virtual Machine.  You can, if you wish, create a shortcut to the VVM progam on your Desktop. Right Click the Desktop. Choose New and then Shortcut. Browse to the program VVM.exe. It should be in the folder C:\Program Files\Visible Virtual Machine. Follw the dialog instructions to finish installing this shortcut.

The first time you execute the Visible Virtual Machine you will be prompted to enter a key. This key is 662-475. This is the only time that you will need this key. However, if you don't have it, you will not be able to use the Visible Virtual Machine.

Accessing VVM From the College of Business Computer Lab

Go to any network machine in A224 or A226. There should be a shortcut on the desktop labelled Visible Virtual Machine. Double click this icon to start the machine. Using VVM When it is executed, your first screen will be.

Click the OK button to proceed to the editor screen.

At this point, you can write your own program by entering code into the window, retrieve previously written files from disk using the File Open menu commands, Validate (check for syntax errors) the current program, or get Help on using the Visible Virtual Machine.  So, Let's retrieve a program.  It's called sample.vvm and can be found in the folder Programs.  You need to use File Open to retrieve this program. After loading it this program, your screen should resemble.

Program lines beginning with the characters // are comments intended for the person reading the code.  A VVM instruction consists of a KeyWord followed, in most cases, by the memory address of the operand.  For example, the second command sto 99 says to copy the value of the accumulator to memory location 99.  Anything appearing after the operand is ignored by the VVM.  Go ahead and Validate the program and then Load it.  The resulting screen is.

The program can executed by clicking on either the Run or Step button.  (We'll try both in class.)  Give it a whirl.  What happens when you input the value 5?  Can you see how the program executes a section of code in memory 5 times to square the original input 5?  Bear in mind, this computer cannot multiply.  It does so by adding, which is much more time consuming than having a multiply instruction.

The VVM has the 5 basic components/capabilities of all digital computers.  These are Input device(s), output device(s), primary memory, secondary storage and a Central Processing Unit (CPU).  While it may seem like a very simple machine when compared to your PC, your PC has the same five components.  And, they work in much the same way as those of the VVM.

I encourage you to look at the other sample programs provided with the Visible Virtual Machine.  Indeed, you might even try your hand at writing your own VVM program.  Here are some suggestions:

• The program named Sample, provided with the VVM, calculates and prints the square of any integer number between 1 and 31. You can load this program by clicking File Open. Select the folder Programs. And finally, select the program Sample As written, this program terminates with a run-time execution error if your initial input is outside this range. Modify the program so it halts whenever it is asked to square a value that is less than 1 or greater than 31.

• Write a program that accepts as input a positive integer value.  The program then computes and sends to the output unit a value indicating the largest multiple of 10 that is less then the original input.  For example, if you input 67, the result should be 6 because 6 * 10 is the largest multiple of 10 that is less than 67.
• Or, write a program that accepts a positive integer input.  It then proceeds into a loop where you are prompted for that many values.  These values are added.  And, the sum is sent to the output device.  For example, if you originally input 4, then the program would prompt you for 4 numbers and print the sum of the 4 numbers you provided.
• Write a program that accepts as input a positive numeric value that is less than or equal to 20. The program should then input this many numbers and print them in the reverse of the order in which they were input.

• Write a program that accepts a positive number between 2 and 20. The program should then read this many numbers, sort them into increasing order and then print them out in increasing order.

Where do you go from here? To start learning to use this machine, I strongly suggest you use the built-in help provided with VVM. It is quite good and covers the basics. And, we will be spending time discussing VVM and writing sample programs for it in class.