gistfile1

100.times do
  100.times do 
    th = Thread.fork do
      File.open("/tmp/thread/#{Thread.current.object_id}", "w") do |io|
        io.puts("a" * 10000)
      end
    end
    th.join
  end
end

100.times do
  100.times do
    Process.fork do
      File.open("/tmp/fork/#{Process.pid}", "w") do |io|
        io.puts("a" * 10000)
      end
    end
  end
  Process.waitall
end

# result
# $ time ruby fork.rb
# ruby fork.rb  17.97s user 32.23s system 110% cpu 45.501 total
# $ time ruby thread.rb
# ruby thread.rb  2.65s user 2.65s system 44% cpu 11.801 total