Halt and poweroff options for shutdown command

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http://unix.stackexchange.com – I have googled for a while, but I still haven't found a clear answer to the differences between halt and poweroff options for shutdown. So I would like to ask this question here. If it helps, my computer is Lenovo T400 and OS is Ubuntu 12.04 Note: I am talking about two options to the command shutdown. Is command halt the same as shutdown -H, and command poweroff the same as shutdown -P? Thanks! (HowTos)