Author: GuruKPO

Overlays are made when there is a need of running a program of larger size than the memory allocated to it. A program is broken into overlays say overlay1 and overlay2, now overlay1 is loaded into main memory and overlay2 is still in secondary memory. When overlay1 finishes its execution, it gets overwritten by overlay2 and it gets executed without loading whole program at a time. Swapping in a scheme in which pages from main memory to secondary memory are being swapped in(rolled in) and swapped out(rolled out) as desired during execution of a process.

OSI is a seven layered architecture used to establish communication between 2 systems which have nothing in common like they are in different networks, having different hardware and software, having different internal architectures. Those seven layers are: physical , datalink, network, transport, session, presentation and application. Each lower layer provides its functionality to the layer above it.