Computer Software

• Software is the set of instructions that tell computers what to do
• Operating systems are required by virtually all computer systems and interact with the hardware, manage resources, and usually present a user interface to the user.
• The user sees one that looks interesting and tries to open it, but their user account is not granted access to open this file.
• The kernel facilitates multi-tasking by performing context switching, where the state of a process and any pertinent data are stored so that execution can switch to a different process.
• A modern OS contains software that simplifies the process of networking, for example, a smart phone connecting to a data service via WiFi.
• A user is logged in to Windows and launches File Explorer, which shows files on the system.
• The CPU disables interrupts and calls the appropriate function when an interrupt occurs.
• The kernel operates in two different modes, User mode and Kernel mode.
• The kernel keeps track of this, and informs the CPU when an attempt is made to access memory locations outside of that space.
• Some applications run in kernel mode, such as device drivers.
• Every application that runs in user mode will have its own, unshared memory.
• A multi-user operating system allows multiple users to access the resources of a single system simultaneously.