If you want to find patterns, you have to look at lots of systems. We need to preserve old systems so that we can look in them for patterns. So, this is a list of pages that describe old computer systems. Please add any you find.
Collections of software
Computer History Simulation Project simh.trailing-edge.com 
Emulators for 19 older machines, all of which run on a Mac. www.bannister.org
Historic Software collection (to be..) home.arcor.de
Borland's Antique Software Museum (yes, Turbo Pascal 3.02 will run on windows XP!) bdn.borland.com
Museums
Obsolete Computer Museum www.obsoletecomputermuseum.org
Computer collection at Goettingen, Germany www.c-c-g.de
Emphasis on sociological impact in this collection at Padua, Italy www.fwtunesco.org
Computer Museum History Center www.computerhistory.org
Online Virtual Computer History Museum:
video.dlib.vt.edu
Iain Fleming's Historic Computers www.galactic.co.uk
The Gentry Collection of Mature Computers:
world.std.com
Vintage Computer Festival:
www.vintage.org
History of microprocessors bwrc.eecs.berkeley.edu
Jay Jaeger's Computer Collection:
webpages.charter.net
Focused on one line of hardware or software
CP/M www.cpm.z80.de
Xerox workstations www.spies.com
ICL/ 3 Rivers Perq workstations (1st 3 M machine) www.access.digex.net
The Online Symbolics Museum smbx.org (see also www.sts.tu-harburg.de )
Multics www.multicians.org
Doug Engelbart's system at Doug Engelbart Symposium
Butler Lampson's personal history www.research.microsoft.com
The Museum of HP Calculators www.hpmuseum.org - Includes may links to other Old Computer sites.
EDSAC simulator:
www.dcs.warwick.ac.uk
Old DEC computers:
www.pdp8.com
PDP-11 Links and Resources:
www.pdp11.org
VAX Archive:
hardware info, resources, etc: www.vaxarchive.org
IBM 1130 History, Emulator, Software and Resources:
www.ibm1130.org
Jef Raskin's Canon Cat:
usemod.com
Other computer history
Computers at Columbia www.columbia.edu
Also see Computer Industrial Archaeology, Really Old Iron.
See original on c2.com