What are over lays?
If a large process enters which is huge than the available memory we are able to use overlays. In this we can divide process into pieces .which is recognized as overlays. Overlay 0 will implement first. After the implementation of 0, it will call another overlay to implement. A few overlay systems were highly complex, permitting multiple overlays in memory at once. The idea of overlay is to remain in memory only those instructions are needed at any given time.