Windows Phone 8 device manufacturers are obligated to produce phones that have at least 512MB of RAM.
Although many phones have more than 512MB of RAM, be mindful of the minimum specification and aim to support the lowest common denominator. Do not assume your app will be running on a device with more than 512MB of RAM. Regardless of how much memory the device has, your app’s memory is capped at either 150MB for lower memory phones or 300MB for higher memory phones. The ID_FUNCCAP_EXTEND_MEM capability can be added to your WMAppManifest.xml file to grant more memory to your app. See http://bit.ly/13o7Pmu for details.
To determine how much memory your app has to work with, use the