Help me memory problem

OS: Windows7 32bit
main memory : 4GB
ruby -v : ruby 1.8.6 (2008-08-11 patchlevel 287) [i386-mswin32]

# big.mkv file size : 1.45GB

ex1.rb

···

--------------------------------------------
puts $$

File.open("D:/test/big.mkv", "rb") do |f|
  while buff = f.read(4096)
  end
end
--------------------------------------------

ex1.rb is OK!! memory usages is about 19,756 KB.

But...

ex2.rb
--------------------------------------------
puts $$

th1 = Thread.new do
  loop do
    sleep 1
  end
end

File.open("D:/test/big.mkv", "rb") do |f|
  while buff = f.read(4096)
  end
end

th1.join
--------------------------------------------

ex2.rb
memory usages is increased continually... after all 1,937,948 KB

I have to use Thread..
Please.. Help Me!!

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