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CSE 2024 Operating System Lecture 1 & 2 Saurabh Mishra, PhD Assistant Professor Dept of CSE Content Introduction to OS Basics of Hardware Basics of Storage Basics of IO Operating System Structure User Interface System Calls  Introduction to Operating System(OS)...

CSE 2024 Operating System Lecture 1 & 2 Saurabh Mishra, PhD Assistant Professor Dept of CSE Content Introduction to OS Basics of Hardware Basics of Storage Basics of IO Operating System Structure User Interface System Calls  Introduction to Operating System(OS) What all are the operating system you have used so far?? Name them The first operating system used for real work was GM-NAA I/O, produced in 1956 by General Motors' Research division for its IBM 704.  Introduction to OS An Operating System(OS) is a program that manages the computer hardware OS also provides a basis for application programs and act as an intermediatory between the computer user and the hardware  Introduction to OS Types of OS Functions of OS Batch Operating System Provide Interface Multi-Programming System Process management Multi-Processing System Resource management Multi-Tasking Operating System Security Time-Sharing Operating System Distributed Operating System Goals of OS Network Operating System Convenience Efficiency Real-Time Operating System  Computer System(Hardware) Basics A modern general purpose computer system consist of one or more CPUs and a number of device controllers connected through a common bus that provide access to shared memory.  Computer System(Hardware) Basics Each device controller is in-charge of a particular device type. The CPU and the device controller can execute concurrently, competing for memory devices To ensure the orderly access to the shared memory, a memory controller is provided whose function is to synchronize access to the memory  Other Basics Bootstrap Process Initial program that runs when the computer is switched on or rebooted It is stored within the computer hardware in read-only memory (ROM) or electrically erasable programmable read-only memory (EEPROM), known by the general term firmware. It must locate and load into memory the OS kernel.  Other Basics Interrupt The occurrence of an event is usually signaled by an interrupt from either the hardware or the software. Hardware may trigger an interrupt at any time by sending a signal to the CPU, through the system bus. System Call(Monitor call) Software may trigger an interrupt by executing a special operation called a system call (also called a monitor call). Other Basics Other Basics When the CPU is interrupted, it stops what it is doing and immediately transfers execution to a fixed location. The fixed location usually contains the starting address where the service routine for the interrupt is located. The interrupt service routine executes. On completion, the CPU resumes the interrupt computation.  Storage Structure Basics The CPU can load instructions only from memory, so any programs to run must be stored there. General-purpose computers run most of their programs from re writable memory, called main memory (also called random- access memory, or RAM). ROM can not be changed, only static programs, such as the bootstrap program are stored there.  Storage Structure Basics All forms of memory provide an array of bytes. Each byte has its own address. Interaction is achieved through a sequence of load or store instructions to specific memory addresses. ✓load ~> The load instruction moves a byte (smallest addressable unit of a CPU) or word (register size or amount of data that can be transferred between CPU and RAM) from main memory to an internal register within the CPU. ✓store ~> The store instruction moves the content of a register to main memory. Storage Structure Basics  I/O operation The main theme of operating system is dedicated to manage I/ O. A general purpose computer system consists of CPUs and multiple device controllers that are connected through a common bus. Each device controller is in charge of a specific type of device. Device Controller maintains local buffer storage and set of special purpose register Depending on the controller, more than one device may be attached. For instance, 7 or more devices can be attached to the small computer-systems interface (SCSI) controller.  I/O operation SCSI devices includes hard disk drives, tape drives, CD/DVD drives, and scanners  I/O operation A device controller maintains some local buffer storage and a set of special-purpose registers. The device controller is responsible for moving the data between the peripheral devices that it controls and it local buffer storage. Typically, operating system have a device driver for each device controller. This device driver understands the device controller and provides the rest of the operating system with a uniform interface to the device. I/O operation Working of an I/O operation To start an IO operation, the device driver loads the appropriate registers within the device controller. The device controller examines the contents of these registers to determine what action to take (like ‘read a character from the keyboard’, ‘display a string’, etc.). The controller starts the transfer of data from the device to its local buffer. When the transfer of data is complete, the device controller informs the device driver via an interrupt that it has finished its operation. The device driver then returns control to the operating system.  I/O operation This form of interrupt-driven I/O is fine for moving small amounts of data but can produce high overhead when used for bulk data movement such as disk I/O. To solve this problem, direct memory access (DMA) is used. After setting up buffers, pointers and counters for the I/O device, the device controller transfers an entire block of data directly to or from its own buffer storage to memory, with no intervention by the CPU. Only one interrupt is generated per block, to tell device driver that the operation has completed, rather than the one interrupt per byte generated for low-speed devices. So, while the device controller is performing these operations, the CPU is available to accomplish other task/operation.  CPU Architecture Single Processor System One main CPU capable of executing a general-purpose instruction set, including instructions from user processes Other special-purpose processors may come in the form of device-specific processors, such as disk, keyboard, and graphics controllers; or, on mainframes. Multiprocessor System Also known as parallel systems or tightly coupled systems Two or more processors in close communication, sharing the computer bus and sometimes the clock, memory, and peripheral devices. Clustered Processor System Composed of two or more individual systems coupled together. Share storage and are closely linked via a local-area network (LAN) provide high-availability service  Operating System Structure Multiprogramming Multitasking/Time sharing  Operating System Structure Multiprogramming Increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to execute. The operating system keeps several jobs in memory simultaneously Operating system keeps several jobs in the memory simultaneously. Since, main memory is too small to accommodate all jobs, the jobs are kept initially on the disk in the job pool. This pool consists of all processes residing on disk awaiting allocation of main memory. Operating system picks and begins to execute one of the jobs in memory. Eventually, if that job have to wait for some task, the CPU switches to another job, and so on. Eventually, the first job finishes waiting and get the CPU back. As long as at least one job needs to execute, the CPU never idle.  Operating System Structure Multiprogramming  Operating System Structure Multitasking/Time sharing Time-sharing (or multitasking) is a logical extension of multiprogramming. In time-sharing systems, the CPU executes multiple jobs by switching among them, but the switches occur so frequently that the users can interact with each program while it is running. Time-sharing requires an interactive computer system, which provides direct communication between the user and the system. The user gives instructions to the operating system or to a program directly, using an input device such as a keyboard, mouse, touchpad, or touch screen, and waits for immediate results on an output device.  Operating System Structure Multitasking/Time sharing  Operating System Services Program execution Input Output Operations Communication between Process File Management Memory Management Process Management Security and Privacy Resource Management User Interface Networking Error handling Time Management  User Operating System Interface There are two fundamental approaches for users to interface with the OS. One technique is to provide a command-line interface or command interpreter that allows users to directly enter commands that are to be performed by the OS. The second approach allows the user to interface with the OS via a graphical user interface or GUI.  Operating System Services Command-line interface or command interpreter Some OSs include the command interpreter in the kernel. Others, such as Windows XP and UNIX, treat the command interpreter as a special program that is running when a job is initiated or when a user first logs on (on interactive systems). On systems with multiple command interpreters to choose from, the interpreters are known as shells. Bourne Shell C-Shell Bourne Again Shell(BASH) Korn Shell, etc  User Operating System Interface Graphical User Interface Rather than having users directly enter commands via a command-line interface, a GUI allows provides a mouse-based window-and-menu system as an interface. Graphical user interfaces first appeared due in part to research taking place in the early 1970s at Xerox PARC research facility. The first GUI appeared on the Xerox Alto computer in 1973. However, graphical interfaces became more widespread with the advent of Apple Macintosh computers in the 1980s. Microsoft's first version of Windows -version 1.O- was based upon a GUI interface to the MS-DOS OS. Traditionally, UNIX systems have been dominated by command-line interfaces, although there are various GUI interfaces available. The choice of whether to use a command-line or GUI interface is mostly one of personal preference. Most Windows users are pleased to use the Windows GUI environment and almost never use the MS-DOS shell interface.  System Call A system call is an interface between a program running in user space and the operating system. A system call is a method for a computer program to request a service from the kernel of the operating system on which it is running. A system call is a method of interacting with the operating system via programs. These calls are generally available as routines written in C and C++ User and Kernel Mode System Call  System Call Types of System calls Process Control File Management Device Management Information Maintenance Communication.  Next Lecture System Programming For any queries: [email protected]