Shell Scripting : How to store output of a command to a variable in shell script?

To store the output of a command to a variable in shell script(also called as command substitution),  there are two methods possible

1) Using backquotes ``
2) Using $( )

Let us see how

# arch=`uname -m`
# echo $arch
x86_64

# arch=$(uname -m)
# echo $arch
x86_64