How to install build-essential without the CD/DVD?

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http://askubuntu.com – I am trying to install the build-essential package per the instructions located here: https://help.ubuntu.com/community/InstallingCompilers I get this error when I use the command apt-get install build-essential: Media change: please insert the disc labeled 'Ubuntu 12.04.1 LTS _Precise Pangolin_ - Release i386 (20120817.3)' in the drive '/cdrom/' and press enter When attempting to install the package through the Ubuntu Software Center, I get the following error: http://i.stack.imgur.com/rMIx5.png Is there any way to install the package online only? (HowTos)