I was installing ubuntu alongside with win 7, and I devoted a full partition for linux during installation. The problem is it didnt install correctly and the 18 GB space cant be found when logging in to win 7 . Please Help.
One thing you could do is to use your installation device USB/CD to log into a live Ubuntu session. For this boot from your device and choose 'Try out Ubuntu'. There your can view your patitions with 'gparted' and change whatever you like.
You should find your lost partition there.
Under Windows 7 you can go to Computer Management and then to Disk Management.
Building on what @joschi said,
Partitions are a way for operating system sto mark the space on your hard drive into sections that can be used separately, for different things. When you installed linux, it would have created one or more of:
To be able to do that, the installer would have looked at the amount of space that Windows was actually using, and then resized it's partition. With this extra space, (18 gb, it seems) it created the extra partitions.
To regain the lost capacity, and make Windows recognize that it's there, you need to: