How to install Ubuntu alongside Windows 7/8 [duplicate]

I have a pre-installed Windows 7/8 and I want to install Ubuntu alongside that. When I try to install I do not have an Install ubuntu alongside windows 7/8 option during the installation (it's missing). How can I have or get back this option?

After installing Windows 7 or 8, you need to have a logical partition to install Ubuntu alongside it. If you don't have a logical partition then the option Install Ubuntu alongside Windows is missing.

To get it back, do the following.

1. Install EASEUS Partition Master Professional Edition (NB: Quite Expensive) or free trial download here

2. Run EASEUS Partition Master then click Go to main screen option.

3. Here, select the partition which you want to install Ubuntu in, and right-click on it and select Delete Partition. Now it's unallocated (Free space).

4. If you don't have this partition you can shrink another one other partition. Just right-click on other partition and select Resize/Move Partition (20GB is enough). Don't format the free space.

5. Now right-click on * unallocated and select Create Partition. Under the Create as drop down, select Logical and click OK.

6. Click the Apply button at the top of EASEUS window (under view menu) then click Yes. This operation needs to restart your computer to completing

7. Finish

If you insert the Ubuntu installation media (USB/DVD) you will see Install Ubuntu alongside Windows 7/8.