UNIX and Shell Programming (10CS44) Unit 1 www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

What is an Operating System (OS)? Functions of an OS Agenda What is an Operating System (OS)? Functions of an OS UNIX Operating System UNIX Architecture www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

What is an Operating System? A program that acts as an intermediary between a user of a computer and the computer hardware. Operating system goals: Execute user programs and make solving user problems easier. Make the computer system convenient to use. Use the computer hardware in an efficient manner. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Computer System Components 1. Hardware – provides basic computing resources (CPU, memory, I/O devices). 2. Operating system – controls and coordinates the use of the hardware among the various application programs for the various users. 3. Applications programs – define the ways in which the system resources are used to solve the computing problems of the users (compilers, database systems, video games, business programs). 4. Users (people, machines, other computers). www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Abstract View of System Components www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Operating System Definitions Resource allocator – manages and allocates resources. Control program – controls the execution of user programs and operations of I/O devices . Kernel – the one program running at all times (all else being application programs). www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Common Services of an OS Process Management Main Memory Management File Management Secondary Storage Management I/O Subsystem Management www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Process Management A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task. The operating system is responsible for the following activities in connection with process management. Process creation and deletion. process suspension and resumption. Provision of mechanisms for: process synchronization process communication www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Main-Memory Management Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices. Main memory is a volatile storage device. It loses its contents in the case of system failure. The operating system is responsible for the following activities in connections with memory management: Keep track of which parts of memory are currently being used and by whom. Decide which processes to load when memory space becomes available. Allocate and deallocate memory space as needed. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

File Management A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. The operating system is responsible for the following activities in connections with file management: File creation and deletion. Directory creation and deletion. Support of primitives for manipulating files and directories. Mapping files onto secondary storage. www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Secondary-Storage Management Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory. Most modern computer systems use disks as the principle on-line storage medium, for both programs and data. The operating system is responsible for the following activities in connection with disk management: Free space management Storage allocation www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

I/O Subsystem Management Keeping track of status of the I/O devices Deciding who gets the device, for how long and when Allocating a device to a process and deallocation www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

The UNIX Operating System Simple and yet powerful A multiuser, multitasking, portable operating system Interaction with the system via a command interpreter – shell On the lighter side, UNIX is simple. But, you need to be a genius to understand its simplicity! www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

UNIX Architecture Shell Kernel Hardware System Calls www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

Division of Labor Kernel Shell in C Core of the OS – a collection of routines/system calls written in C Loaded into memory when the system is booted Communicates with the hardware directly Shell Interface between the user and the kernel Acts as the command interpreter Forms a simpler version of the command line and communicates with the kernel to see that command is executed www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS

End of session www.bookspar.com | Website for Students | VTU NOTES | QUESTION PAPERS