Q: Fusion drive

You can install OS X and Windows on a Fusion Drive, but Windows won't work as fast as OS X. This is caused because OS X is saved in the SSD part of Fusion Drive and Windows is installer in the HDD part of Fusion Drive.

First, check if you need Windows on Boot Camp or a virtual machine > https://discussions.apple.com/docs/DOC-3321 I recommend you to use a virtual machine with applications like Parallels, VMware Fusion or VirtualBox, because it's easier to install Windows.

If you need Boot Camp, follow Apple steps carefully to install Windows on Fusion Drive > http://manuals.info.apple.com/MANUALS/1000/MA1636/en_US/boot_camp_install-setup_ 10.8.pdf

The Intel Iris Pro graphic card has got 1 GB of memory in both 21'5-inch iMacs and 15-inch MacBooks Pro with Retina display

Intel Iris Pro Graphics

Apple computers using Intel Iris Pro Graphics as the primary GPU dynamically allocates up to 1 GB of system memory.

Products with Intel Iris Pro Graphics:

• iMac (21.5-inch, Late 2013)
• MacBook Pro (Retina, 15-inch, Late 2013)

About integrated video on Intel-based Macs

You are welcome