On a 64-bit machine (Ubuntu Karmic):

$ ruby -v
ruby 1.8.7 (2009-06-12 patchlevel 174) [x86_64-linux]

>> Object.constants.map { |c| [c,Object.const_get(c)] }.each { |c,v| p [c,v] if c=~/RUBY/ || v =~ /86/}; nil
["RUBY_DESCRIPTION", "ruby 1.8.7 (2009-06-12 patchlevel 174) 
[x86_64-linux]"]
["RUBY_PLATFORM", "x86_64-linux"]
["RUBY_VERSION", "1.8.7"]
["RUBY_COPYRIGHT", "ruby - Copyright (C) 1993-2009 Yukihiro Matsumoto"]
["RUBY_PATCHLEVEL", 174]
["PLATFORM", "x86_64-linux"]
["RUBY_RELEASE_DATE", "2009-06-12"]
-- 
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