File Permissions in Unix/Linux

File Permissions Unix & Linux provides Read(r),Write(w) and Execute(x) permissions to any file on the system. If you ls -l every file with its permissions will be shown. The system is divided into three types - User,Group and others. The r,w,x permissions are assigned to each type. This is well explained by the diagram shown below: Owner permissions − The owner’s permissions determine what actions the owner of the file can perform on the file.

How Your Computer Starts

Every computer follows a standard boot sequence when it starts up. BIOS (Basic Input Output System) The CPU runs an instruction in memory for the BIOS. This is a Jump instruction that transfers the Instruction Pointer to the code of the BIOS start-up program. The BIOS runs the Power On Self Test. It is a process performed by firmware or software routines immediately after a computer or any digital device is powered on.

Virtualisation in Operating Systems

Virtualisation is the process of creating a virtual version of a physical object. Virtualisation is of three types primarily: 1. Hardware Virtualisation - Based on simulating real hardware. This can be used to run a complete operating system. This can be further subdivided into full and paravirtualisation. Desktop Virtualisation - It is the concept of separating the logical desktop from the physical machine. Operating system level virtualisation (also called as containerisation) - It is the operating system feature in which the kernel allows the existence of multiple isolated user-space instances.