Boot Camp & Partitions

I have a iMac with OS X Yosemite. It has a 1 TB hard Drive and I've successfully installed Boot Camp to run Windows 8.1 as I need software I use for work to run on there. It works perfectly with no issues. Now then, I have a question regarding partitions.

It's currently portioned (Drive D) 900GB for Mac OS and (Drive C) 100GB for Boot Camp/Windows.

Now then, is it possible to create a third partition in the Mac volume (200GB) to be used for Data Storage which will be accessible to read/write by BOTH the Mac & Windows volumes?

It's possible, however, the danger is that it may destroy the Window 8.1 boot sector in the process or may interfere with booting Yosemite. When setting up Boot Camp, it has to be remembered that it only supports one partition other than the normal Yosemite and recovery partitions.

It's probably best to buy an external hard drive, format it to exFAT or even FAT-32 and use it as a common drive for both Yosemite and Windows 8.1.

Thanks chscag... I think that's the safest way forward