This write-up is based on a  research paper  by Jeffrey S. Chase et al, University of Washington. The above-mentioned research paper takes into consideration the sharing and protection in Opal Operating system. Opal is a single-address-space operating system intended to support complex applications on wide-address architectures. Opal provides a single global virtual address space that is shared by all procedures and data.  The Wide-address architectures facilitate the single-address approach by eliminating the need to reuse addresses, which is required in a 32-bit architecture. Looking a little into private space approach, the major advantage of private spaces are: The amount of address space available to all programs increases. Hard protection boundaries are provided.  Easy cleanup when a program exits.         The disadvantages of this approach are: Isolating programs within private virtual address spaces presents obstacles to efficient cooper