I just updated Android SDK to version 21 and trying to start emulator. I am using Nexus 4 with CPU Intel atom (x86) 768 RAM and 524 internal storage. Emulator starts fine but it
Go to AVD manager on your android studio.
click on the pencil icon of the virtual device.
on the pop up window click on advanced settings at the bottom.
scroll down to memory and storage and alter the default definitions of MB/GB etc.