Difference between two commands.

*To*: mathgroup at smc.vnet.net*Subject*: [mg90474] Difference between two commands.*From*: Budaoy <yaomengliang at gmail.com>*Date*: Thu, 10 Jul 2008 06:36:45 -0400 (EDT)

What's the difference between these two commands: << and Needs? Sometimes we use <<Graphics` and sometimes we use Needs["ComputerArithmetic`"]. Where do they distinguish from each other?