So, you are one of the many people who have freshly installed Ubuntu 9.10 on your system, yet not completely fallen in love with it as at some corner of the hard disk, you have still windows installed. Now you have a dual boot menu, GRUB and wondering how to change the default OS to windows.(Whenever a new version of Ubuntu is installed, the bootloader will always point to Ubuntu itself.
You switch on the computer and come across with number of weird options in GRUB starting with Ubuntu, memtest, something else and last option is reserved for windows..(Is it a race or something?)
Here is how you can change the default OS to windows:
1. Login to Ubuntu
2. open the terminal => Alt+F2 => type gnome-terminal
3. at the prompt,type
sudo gedit /etc/default/grub
4. The system will ask for an admin password as you are trying to make changes to one of the important files
5. in the editor, search for the parameter GRUB_DEFAULT, It will be set to 0(for Ubuntu) by default
6. change the value to 2,3,4 (wherever the option of windows is indexed at in the GRUB). Typically, it is 4 in a dual boot.
7. save the file
8. you will return back to the terminal

9. type in
sudo update-grub
This will regenerate the file /boot/grub/grub.cfg

You are done. The next time you see the GRUB, the default pointer will be at windows OS.

1. Performance: Usage of single-quotes is more performance friendly than using double quotes (will be more clear in the following points)

2. Expression intrapolation: It simply means if you want to process any of the expression or want to print a value of the variable, the double quotes should be used. Single quotes never parses any expression enclosed in them. You can even insert a full fledged code in double quotes. The interpreter will simply process the code in double quotes first and print the resultant

In Single quotes:

name = “Some String”
puts ‘#{if name==”Some String”
puts “Hello, Some String”
else
puts “Hello, Specific String”
end
}’        # will print the code as it is without any processing

In Double Quotes

name = “Some String”
puts “#{if name==“Some String”
puts “Hello, Some String”
else
puts “Hello, Specific String”
end
}”                       # will print “Hello, Some String”

3. Variable Substitution: If any value needs to be printed using puts and you must use a double quote

name = “Some String”
puts “#{name}“ # will print Some String as a result
puts ‘#{name}’ # will print #{name} as a result

4. Escape Sequence: The scope of usage of escape sequences broadens when you use double quotes. There are many options with double quotes to include escape sequences as compared to the ones in single quotes.