At the time of writing, the Unity engine itself uses up around 60 MB of memory (often referred to as its memory footprint) on an iOS device. On an iPad 3 with its 1 GB of RAM, this is no problem, but on an iPhone 3G, that’s nearly half of your memory budget eaten up. This leaves you with just 68 MB for music, sound, 3D models, textures, and other game assets. If you are aiming to support older iOS devices such as the iPhone 3G or iPod Touch third generation, you are more than likely going to have to compress things-from audio to textures.