What is the maximum ram for MacBook Pro retina?

16GB memory last I saw.

 

16GB, which is shown on Apple's site.

No, you can't put a HDD in the rMBP, which uses Flash storage, not traditional HDD or SSD enclosures.

You can find specs on all Apple products, including maximum RAM:

• By visiting EveryMac.com: Actual Maximum RAM
• By selecting your model on the Crucial Memory Advisor™ Tool to find RAM information
• By using Mactracker
• By entering your serial number here to find specs for your model. (Be aware that some models can use more RAM than Apple shows. Check EveryMac to verify actual usable RAM.)

 

Well, you could get a "hi-res" MacBook Pro, but that won't be as high as a laptop with a full 1080p display, which is about as good as you're going to get over in Windows land. You're not going to find anything in the laptop market currently that competes with the Retina display.

 

There have been some ultrabooks announced very recently with similar high res screens (Asus Zenbook Infinity is one example).

Most of those will probably have at least partially soldered memory, and usually an msata style SSD that cannot be replaced with a normal HDD.

Edit: The Fujitsu Lifebook UH90 has a 500GB hybrid HDD/SSD, but so far only has a release date in Japan.

http://www.engadget.com/2013/06/05/fujitsu-intros-lifebook-uh90-ultrabook/

 

You don't need to put a hard drive in a retina MacBook Pro. Just use an external drive if the internal storage is not sufficient.