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Chapter 1 Introduction 1.1 What is an operating system 1.2 History of operating systems 1.3 The operating system zoo 1.4 Computer hardware review 1.5 Operating system concepts 1.6 System calls 1.7 Operating system structure 1 Introduction • A computer system consists of – hardware – system programs – application programs 2 What is an Operating System • It is an extended machine – Hides the messy details which must be performed – Presents user with a virtual machine, easier to use • It is a resource manager – Each program gets time with the resource – Each program gets space on the resource 3 History of Operating Systems (1) • First generation 1945 - 1955 – vacuum tubes, plug boards • Second generation 1955 - 1965 – transistors, batch systems • Third generation 1965 – 1980 – ICs and multiprogramming • Fourth generation 1980 – present – personal computers 4 History of Operating Systems (2) Early batch system – – – – bring cards to 1401 read cards to tape put tape on 7094 which does computing put tape on 1401 which prints output 5 History of Operating Systems (3) • Structure of a typical FMS job – 2nd generation 6 History of Operating Systems (4) • Multiprogramming system – three jobs in memory – 3rd generation 7 The Operating System Zoo • • • • • • • Mainframe operating systems Server operating systems Multiprocessor operating systems Personal computer operating systems Real-time operating systems Embedded operating systems Smart card operating systems 8 Computer Hardware Review (1) Monitor Bus • Components of a simple personal computer 9 Computer Hardware Review (2) (a) A three-stage pipeline (b) A superscalar CPU 10 Computer Hardware Review (3) • Typical memory hierarchy – numbers shown are rough approximations 11 Computer Hardware Review (4) Structure of a disk drive 12 Computer Hardware Review (5) One base-limit pair and two base-limit pairs 13 Computer Hardware Review (6) (a) (b) (a) Steps in starting an I/O device and getting interrupt (b) How the CPU is interrupted 14 Computer Hardware Review (7) Structure of a large Pentium system 15 Operating System Concepts (1) - Processes • • • • • A process is a program in execution Swapping of a process – Process table entry System calls to create and terminate processes System calls to allocate/deallocate memory System calls for communication - signals 16 Operating System Concepts (2) - Processes • A process tree – A created two child processes, B and C – B created three child processes, D, E, and F 17 Operating System Concepts (3) -Deadlocks (a) A potential deadlock. (b) an actual deadlock. 18 Operating System Concepts (4) - Files • Present the programmer with nice, clean, abstract, device-independent files. • Concept of directory to group files together • System calls to create/remove directories and create/remove files. Hierarchies. • Process trees != Directories • A file can be specified by a path name: absolute (from root), relative (from current working directory). 19 Operating System Concepts (5) - Files File system for a university department 20 Operating System Concepts (6) - Files • Protection of files and directories, e.g. UNIX the rwx bits: 9 bits (owner/group/others) rwxr-xr-• File Descriptor: a number assigned to a file. • Mounting file systems. • Special files: block special files, character special files – standard input (fd=0), standard output (fd=1), standard error (fd=2). 21 Operating System Concepts (7) - Files • Before mounting, – files on floppy are inaccessible • After mounting floppy on b, – files on floppy are part of file hierarchy 22 Operating System Concepts (8) - Pipes Two processes connected by a pipe. Read/Write - transparent for processes. 23 Operating System Concepts (8) - Shell • The shell is a program that acts as an interface between the user and the OS. • Unix: several shells (e.g. csh, ksh). • MSDOS: command prompt. • Prompt, process, std input, output, creates processes. 24 Steps in Making a System Call There are 11 steps in making the system call read (fd, buffer, nbytes) 25 Some System Calls For Process Management 26 Some System Calls For File Management 27 Some System Calls For Directory Management 28 Some System Calls For Miscellaneous Tasks 29 System Calls (1) • A stripped down shell: while (TRUE) { type_prompt( ); read_command (command, parameters) /* repeat forever */ /* display prompt */ /* input from terminal */ if (fork() != 0) { /* Parent code */ waitpid( -1, &status, 0); } else { /* Child code */ execve (command, parameters, 0); } } /* fork off child process */ /* wait for child to exit */ /* execute command */ 30 System Calls (2) • Processes have three segments: text, data, stack 31 System Calls (3) (a) Two directories before linking /usr/jim/memo to ast's directory (b) The same directories after linking 32 System Calls (4) (a) File system before the mount (b) File system after the mount 33 System Calls (5) Some Win32 API calls 34 Operating System Structure • • • • Monolithic Layered Virtual Machines Client-Server 35 Operating System Structure (1) User program 1 User program 2 Kernel call 4 1 Service procedure 3 2 dispatch table 36 Operating System Structure (1) Simple structuring model for a monolithic system 37 Operating System Structure (2) Structure of the THE operating system 38 Operating System Structure (3) Structure of VM/370 with CMS 39 Operating System Structure (4) The client-server model 40 Operating System Structure (5) The client-server model in a distributed system 41 Metric Units The metric prefixes 42