OPERATING SYSTEMS DO YOU REQUIRE AN OPERATING SYSTEM IN YOUR SYSTEM?

Need for an OS Adding two numbers Since we have an already written library, namely the OS To add two numbers we simply write the following line to our program: c = a + b ;

In a system where there is no OS installed, we should consider some hardware work as: (Assuming an MC 6800 computer hardware) LDAA $80  Loading the number at memory location 80 LDAB $81  Loading the number at memory location 81 ADDB  Adding these two numbers STAA $55  Storing the sum to memory location 55 We considered memory locations and used our hardware knowledge of the system. Need for an OS

In an OS installed machine, since we have an intermediate layer, our programs obtain some advantage of mobility by not dealing with hardware. For example, the above program segment would not work for an 8086 machine, where as the “c = a + b ;” syntax will be suitable for both. Need for an OS

Operating Systems A simple program segment with no hardware consideration A more sophisticated program segment with hardware consideration Hardware response OS Machine Language

Operating Systems In a more simplistic approach, in fact, OS itself is a program. But it has a priority which application programs don’t have. OS uses the kernel mode of the microprocessor, whereas other programs use the user mode. The difference between two is that; - all hardware instructions are valid in kernel mode, where some of them cannot be used in the user mode.

What is an Operating System? A modern computer consists of: One or more processors Main memory Disks Printers Various input/output devices. Managing all these varied components requires a layer of software – the Operating System (OS).

A good OS should be easily usable by everyone

What’s in an OS? Machine Dependent Services Interrupts, Cache, Physical Memory, TLB, Hardware Devices Generic I/O File System Memory Management Process Management Virtual Memory Networking NamingAccess Control Windowing & graphics Windowing & Gfx Machine Independent Services SYSTEM CALL API MD API Device Drivers ShellsSystem Utils QuakeSql Server Logical OS Structure

provides supports for other programs. It is responsible for loading other programs into memory for execution. However, the operating system itself is a program that needs to be loaded into the memory and be run. How is this dilemma solved? Operating Systems

Bootstrap process The solution is a two-stage process. A very small section of memory is made of ROM and holds a small program called the bootstrap program. When the computer is turned on, the CPU counter is set to the first instruction of this bootstrap program and executes the instructions in this program. When loading is done, the program counter is set to the first instruction of the operating system in RAM.

What is an Operating System? An operating system (OS) is: –a software layer to abstract away and manage details of hardware resources –a set of utilities to simplify application development –“all the code you didn’t write” in order to implement your application Applications OS Hardware

OS-Making the Computer Work for You Operating Systems –A collection of programs that manage and control all operations and coordinate all hardware components of the computer. –Some functions include: Controlling the mouse pointer. Sending data to the printer and screen. Managing files. Formatting disks. –Popular Operating Systems include Windows, Unix, MacOS, VMS, Linux, OS/2.

Operating System A program that controls the execution of application programs An interface between applications and hardware

Operating System Objectives Convenience Efficiency Ability to evolve

Layers and Views

OS-Making the Computer Work for You Utilities –Help to keep the computer running properly by: Making adjustments in efficiency. –Faster operation. –More efficient memory and hard disk use. –Better communication connections. Making repairs to damaged disks and files. Identifying and eliminating viruses.

20 Operating System Views Resource allocation to allocate resources (software and hardware) of the computer system and manage them efficiently. Control program Controls execution of user programs and operation of I/O devices. Kernel The program that executes forever (everything else is an application with respect to the kernel).

21 Abstract View of System System and Application Programs Operating System Computer Hardware Computer Hardware User 1 User 1 User 2 User 2 User 3 User 3 User n User n compilerassembler Text editor Database system...

OPERATING SYSTEM OVERVIEW The Layers Of A System Program Interface Humans User Programs O.S. Interface O.S. Hardware Interface/ Privileged Instructions Disk/Tape/Memory

Software layers ROM Hardware Operating System User Interface Software Files CPU, RAM, HD, DVD Word, scripts, mail, web browser… Data (.doc,.mp3) BIOS Linux CLI, X-Windows Windows MacOSX Firmware Quartz