Sapphire 7770 Vapor X only 703mb memory?

Honestly I wouldnt worry about it.

Why? Is it a known issue on dxdiag?? I just wanna make sure it isn't a defective hardware so I could RMA immediately

my 6850 only shows 734mb in dxdiag. but GPU-Z, which is more reliable, shows the full 1024.
you can download GPU-Z here:
http://www.techpowerup.com/downloads/2157/TechPowerUp_G...

GPU-Z is what I use. It shows all the information about the card, such as the core and the memory bus.

It's probably just showing the RAM that is not allocated.

I downloaded GPU-Z and it says 1024mb memory so I guess it's a dxdiag problem? Hmmm, weird..............

https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-ash4/...

Well, it looks like you have all the memory, so I wouldn't worry about it.