I am currently rendering a animation and it will take a long time but before I let it run for hrs I want to know if every frame of the animation is stored in RAM because my PC only has 2 GB and I don't want blender to stop half way through and have to start again. If this is a issue is there a way to render part of a animation and do the rest later?
No, they're not stored in RAM. For image sequence output, each frame rendered will be immediately written to the disk. Even video output using FFMPEG directly writes to the disk by chunks.
I've tried rendering CG animation directly to video (not recommended) for hours, and there's no sign of increasing memory usage over time.