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The M5 Simulator System
A modular platform for computer system architecture research


  • M5 is a modular platform for computer system architecture research, encompassing system-level architecture as well as processor microarchitecture.


  • M5 is slowly moving away from SourceForge to our own server at: which you're using right now. This machine will host the M5 website, Mailing Lists, bug tracking, and source repository in the near future.


  • The current public release of M5 is available on our Download page. Please look at the sidebar for links to file bugs and for mailing list subscription information.

Key features

  • Pervasive object orientation. Major simulation structures (CPUs, busses, caches, etc.) are represented as objects, both externally and internally. M5's configuration language allows flexible composition of these objects to describe complex simulation targets, e.g., multi-system networks where each system comprises multiple CPUs and a hierarchy of caches. M5's internal object orientation (using C++) provides in addition to the usual software engineering advantages.
  • Multiple interchangeable CPU models. M5 currently provides three interchangeable CPU objects: a simple, functional, one-CPI CPU; a detailed model of an out-of-order SMT-capable CPU; and a random memory-system tester. The first two models are use a common high-level ISA description.
  • Event-driven memory system. M5 features a detailed, event-driven memory system including non-blocking caches and split-transaction busses. These components can be arranged flexibly, e.g., to model complex multi-level cache hierarchies. The caches support a separable coherence policy module; M5 currently includes a simple snooping cache coherence protocol.
  • Full-system capability. M5 models a DEC Tsunami system in sufficient detail to boot unmodified Linux 2.4/2.6, FreeBSD, or L4Ka::Pistachio. We have also booted HP/Compaq's Tru64 5.1 operating system in the past, though we no longer actively maintain that capability.
  • Multiprocessor / multi-system capability. Thanks to M5's object orientation, instantiation of multiple CPU objects within a system is trivial. Combined with the snooping bus-based coherence protocol supported by the caches, M5 can model symmetric multiprocessor systems. Because a complete system is just a collection of objects (CPUs, caches, memory, etc.), multiple systems can be instantiated within a single simulation process. In conjunction with full-system modeling, this feature allows simulation of entire client-server networks.

Additional details

  • Application-only support. In application-only (non-full-system) mode, M5 can execute Alpha Linux or Tru64 binaries with OS emulation or SimpleScalar EIO trace files.
  • Platforms. M5 runs on Intel x86-compatible systems running Linux, OpenBSD, or Cygwin, and should be readily portable to other little-endian hosts and other Unix-like operating systems. Alpha binaries to run on M5 (including the full Linux kernel) can be built on x86 systems using gcc-based cross-compilation tools, so no Alpha hardware is needed to make full use of M5.
  • Provenance. Portions of M5 (EIO trace support and parts of our old detailed CPU model) were derived from SimpleScalar. These portions are being released under the SimpleScalar license. We have a new detailed CPU model that will eliminate this dependency, though this new model currently does not support full-system simulation or SMT. We are also grateful to the SimOS and SimOS/Alpha developers, as SimOS/Alpha was an invaluable reference platform during our development of full-system mode.
  • Licensing. M5 is being released under a Berkeley-style open source license. Roughly speaking, you are free to use our code however you wish, as long as you leave our copyright on it. For more details, see the LICENSE file included in the source download. Note that the portions of M5 derived from other sources are also subject to the licensing restrictions of the original sources (notably SimpleScalar).


  • Overview and specific documentation about M5 is available on the Documentation page. Additionally, the M5 code is commented with doxygen comments. You can browse the doxygen-generated documentation here.
  • The slides and handouts from our ISCA-33 tutorial held June 18, 2006 in Boston are available for downloading. (The slides and handouts are the same except for formatting; the handouts are two slides per page.) This tutorial covers the 2.0 release. Slides and handouts from our ISCA-32 tutorial held June 5, 2005 in Madison are also available; these are dated as they describe M5 v1.X rather than v2.
  • A more detailed discussion of M5 can be found in our article The M5 Simulator: Modeling Networked Systems from the July/Aug 2006 issue of IEEE Micro. If you use M5 in your research, we would apreciate a citation to this paper in any publications you produce.


A list of publications using the M5 simulator is also available. Please append to the list if you publish a paper using M5.


The M5 simulator is being developed with generous support from several sources, including the National Science Foundation, Hewlett-Packard, Intel, IBM, MIPS, and Sun. Individuals working on M5 have also been supported by an Intel Fellowship (Nate Binkert), a Lucent Fellowship (Lisa Hsu), and a Sloan Research Fellowship (Steve Reinhardt).

This material is based upon work supported by the National Science Foundation under Grant Nos. CCR-0105503 and CCR-0219640. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

Why is it called M5?