Dual Boot

How to remove an operating system after dual booting??

Post back a screenshot of Disk Management - Post a Screen Capture Image
from the OS you want to keep.

No,mr gregrocker,i had not installed dualboot OS,iam with windows 7 ultimate 64 bit.After suggestion,i want to dual boot windows 8 and want to know how to remove it...

The System boot files which were likely previously on that 100mb partition have been moved onto C so that it is booting itself, and it looks correct.

So you can Clean Install - Windows 8 on any of those other partitions and it should configure a Dual Boot with Win7. Always install any OS by booting the installer to avoid problems. Be sure to format the chosen partition after backing up any data from it.

Be aware that you may only have four primary partitions so if you try to create another it may convert your hard disk to Dynamic which you do not want as it will not boot an OS, and is only used to span a partition across multiple drives. If you need more partitions you must first convert one of the data partitions to Logical and then you can add as many adjacent Logical sub-partiitons as you want. A Logical partition can host an OS but not its boot files, however in a Multi-Boot System the System boot files will remain on the first installed OS or its System Reserved partition, which is not being used on this install.

Partition / Extended : Logical Drives - Windows 7 Forums
How to Set Partition as Primary or Logical
Partition Wizard Resize Partition - Video Help.
Partition or Volume - Create New