Operating System Generation System Boot Unit 1 S. Prabhavathi, AP/IT 1 Operating System Generation(SYSGEN) • Designing and implementing an operating system specifically for one machine at one site is a concern about that specific machine only • Operating systems are designed to run on any of a class of machines at a variety of sites with a variety of peripheral configurations. • The system must be configured for each specific computer site, a process sometimes known as system generation SYSGEN. • SYSGEN program obtains information concerning the specific configuration of the hardware system • Bootstrapping – code stored in ROM that is able to locate the kernel, load it into memory. • Booting: Start of the actual execution of the OS Unit 1 S. Prabhavathi, AP/IT 2 Operating System Generation(Contd) The following kinds of information must be determined by SYSGEN program: • What CPU is to be used? • How much memory available? • Boot disk partition • What devices available, type, model, interrupt number etc? • What operating system options are desired, CPU scheduling algorithm, number of processes support? (uses .config file) Based on the system description, operating system is generated. Unit 1 S. Prabhavathi, AP/IT 3 System Boot Boot Process Unit 1 S. Prabhavathi, AP/IT 4 System Boot • The procedure of starting a computer by loading the kernel is known as booting the system. • When power initialized on system, execution starts at a fixed memory location – Firmware ROM used to hold initial boot code • Operating system must be made available to hardware so hardware can start it – Small piece of code – bootstrap loader or bootstrap program, stored in ROM or EPROM locates the kernel, loads it into memory, and starts it execution – Sometimes two-step process in which a simple bootstrap loader fetches a more complex boot program from disk. – This boot program in turn loads the kernel. Unit 1 S. Prabhavathi, AP/IT 5 System Boot • Bootstrap program can perform a variety of tasks: ! determines the state of the machine ! Initializes CPU registers to device controllers and the contents of main memory. • Bootstrap loader is stored in firmware, and the operating system is on disk. • Bootstrap read a single block at a fixed location (say block zero) from disk into memory and execute the code from that boot block. • Common bootstrap loader in Linux systems, GRUB, traverse the file system to find the operating system kernel, load it into memory, and start its execution. • Kernel loads and system is said to be running Unit 1 S. Prabhavathi, AP/IT 6 Thank You Unit 1 S. Prabhavathi, AP/IT 7 .