CPU Sim

An Interactive Java-based CPU Simulator for use in Introductory Computer Organization Classes

Written and maintained by Dale Skrien
Department of Computer Science
Colby College
Waterville ME 04901
Email: djskrien@colby.edu
Author's home page: http://www.cs.colby.edu/djskrien/

Summary

CPU Sim is a Java application that I wrote that allows users to design simple computer CPU's at the microcode level and to run machine-language or assembly-language programs on those CPU's through simulation. It can be used to simulate a variety of architectures, including accumulator-based, RISC-like, or stack-based (such as the JVM) architectures. It is a useful tool for instructors who want their students to get hands-on exposure to a variety of architectures and to get a chance to design and implement their own architectures and write programs in machine language and assembly language for their architectures.

CPU Sim was written using the Swing package. It should run on any platform that has the Java runtime environment, JRE version 1.5 or later, installed on it. I have tested it on Windows, Linux, and Macintosh (OS X) platforms.

Features

• Tools for designing a CPU at the register-transfer level:
  • Dialogs for specifying the number and width of registers, register arrays, and RAMs.
  • Dialogs for specifying the microinstructions (e.g., bit transfers between registers) that are used to implement the machine instructions
  • A dialog for specifying the machine instructions, including:
    • the number of bits in each instruction
    • the opcode value and the number of bits the opcode occupies
    • the number of the operands and the number of bits in each operand
    • the semantics of each instruction (specified by a sequence of microinstructions)
• A text editor for writing assembly language programs
• An assembler for converting assembly programs into machine code for the user's CPU.
• A debugger for stepping forward and backward through the execution of such programs, inspecting and optionally changing the machine state after each step.

To get a better feeling for the user interface of CPU Sim, I have made available some pictures of the dialog boxes, windows, and menus.

Newest Version

The latest stable version of CPU Sim is 3.8.1. It runs under Java 1.5 or later.

Downloads

CPU Sim is freeware. You can download a 5 MB zip file containing version 3.8.1 of the CPU Sim package. Here is what is new in version 3.8.1. The installation instructions explain what is in the zip file and how to install and start up the package. If you wish, you can view or download just the User's Manual (in PDF). NOTE: The User's Manual has not yet been updated to reflect the changes added since version 3.4.1, but the online help in CPU Sim has been updated.

An earlier version, CPU Sim 3.6.9 is still available here (including the installation instructions).

An instructor's manual including sample programming projects and their solutions is also available. Please contact me at djskrien@colby.edu if you are interested in these supplementary materials.

Previous Versions

I wrote versions 1 and 2 of CPU Sim in the early 1990's using Macintosh Common Lisp and, as a result, they ran only on the Macintosh platform. Version 2.2 of this software won the 1993 EDUCOM Higher Education Software and Curriculum Innovation Award for Best Engineering Software (Computer Science). It was one of only 10 winners out of over 140 entries. A Macintosh Common Lisp-based version (2.6.5) is still available in both MC680x0-native and PowerPC-native forms. These are the only versions of CPU Sim that run on MacOS 9 and earlier.

Please contact me at djskrien@colby.edu if you are interested in these earlier versions.

Articles about CPU Sim and its precursor

KERRIDGE, J., AND WILLIS, N. 1980. A Simulator for Teaching Computer Architecture. SIGCSE Bulletin, 12(2), 65-71.
This simulator is the precursor to CPU Sim.

SKRIEN, D., AND HOSACK, J. 1991. A multilevel simulator at the register transfer level for use in an introductory machine organization class. SIGCSE Bulletin (Papers of the 22nd ACM/SIGCSE Technical Symposium on Computer Science Education), 23(1), 347-351.
This article describes version 1.0.13 of CPU Sim.

SKRIEN, D. 1994. CPU Sim: A Computer Simulator for Use in an Introductory Computer Organization Class. Journal of Computing in Higher Education, 6(1), 3-13.
This article describes version 2.2 of CPU Sim.

SKRIEN, D. 2001. CPU Sim 3.1: A tool for simulating computer architectures for computer organization classes. ACM Journal of Educational Resources in Computing (JERIC) 1(4), 46-59. This issue of JERIC is a special one devoted to computer architecture simulators.

I also presented a faculty poster at SIGCSE 2002 about CPU Sim 3.1.

This page was last updated on December 6, 2012.