altogether: a Xerox Alto simulator

Altogether is a microcode-level simulator for the Xerox Alto personal workstation.


Altogether currently simulates the Alto CPU and video display, though the display is not quite correct. The disk code is incomplete. See the related work section below for more details.


Altogether is made available under the terms of the Free Software Foundation's General Public License, Version 2.

Source code to a very preliminary release is available for download.

Altogether development uses the Subversion revision control system. Instructions for access to the Subversion repository for Altogether are found at, and there is a web interface to browse the repository at

mailing lists

There are two mailing lists for Altogether:

There is also a mailing list for general Alto discussion:

related work

Juergen Buchmueller has been doing a lot of work on Alto simulation recently, based in part on Altogether. He has uncovered undocumented aspects of how the display and disk controllers work, and written his own simulator Salto, which now can almost boot from disk. He's documented his work at

additional resources

Last updated June 21, 2007

Copyright 2003, 2007 Eric Smith

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