Chapter 1What is UNIX?Graham Glass and King Ables, UNIX for Programmers and Users,Third Edition, Pearson Prentice Hall, 2003.Original Notes by Raj SunderramanConverted to presentation and updated by Michael Weeks1/7/2008 cs3320 2Computer Systems• Computer System : Hardware + Software• Hardware: CPU, Memory (RAM/ROM), Disk drives, CD-ROM drives, Monitor, Graphics card, Keyboard, Mouse, Printer, Tape drive, Modem, Ethernet interface, Other peripherals.• Software: Operating System, Application Programs• UNIX is the name of a popular operating system.1/7/2008 cs3320 3Typical Personal Computer System1/7/2008 cs3320 4Hardware Key Components (1) : CPU and Main MemoryCentralProcessingUnitMainMemoryChip that executes program commandsIntel Pentium 4 orSun ultraSPARCIII ProcessorPrimary storage area for programs and data that are in active useSynonymous with RAM1/7/2008 cs3320 5Hardware Key Components (2) : Secondary Memory DevicesFloppy DiskHard DiskMainMemoryCentralProcessingUnitSecondary memorydevices providelong-term storageInformation is movedbetween main memoryand secondary memoryas neededHard disksFloppy disksZIP disksWritable CDsTapes1/7/2008 cs3320 6Hardware Key Components (3) : Input / Output DevicesMonitorKeyboardMainMemoryCentralProcessingUnitFloppy DiskHard DiskI/O devices facilitate userinteractionMonitor screenKeyboardMouseJoystickBar code scannerTouch screen1/7/2008 cs3320 7REMOVABLEMEDIAUSERMODEM +TELEPHONELOCAL AREANETWORKREMOTELOCATIONINTERNETCONNECTION“BACKDOOR”INTERNETCONNECTIONISPREMOTEUSERVENDORS ANDSUBCONTRACTORSRADIOEMISSIONSWIRELESSUSERRADIOEMISSIONSComputer Network1/7/2008 cs3320 8Software Component• Applications• Operating System– API: application program interface– File management– I/O– Kernel• Memory management• Resource scheduling• Program communication• Security– Network Module1/7/2008 cs3320 9Software Categories• Operating System– controls all machine activities– Oversee operation of computer - Store and retrieve files– Schedule programs for execution - Coordinate the execution of programs - Provides the user interface to the computer– manages resources such as the CPU and memory• Application program– generic term for any other kind of software– word processors, missile control systems, games• Most operating systems and application programs have a graphical user interface (GUI)1/7/2008 cs3320 10The shell as an interface between users and the operating system1/7/2008 cs3320 11Figure 3.5 The booting process1/7/2008 cs3320 12UNIX is an operating systemfile store programsnetworks etc.UNIXIt manages:¥ files and data¥ running programs¥ networks and other resourcesIt is defined by¥ its behaviour (on files etc.)¥ its application programmers interface Ð API● Provides a framework for executing programs and storing files●File: collection of data normally stored on disk.●Program: collection of instructions/data that is stored in a file.1/7/2008 cs3320 13UNIX API – the system callsultimately everything works through system callsshellfile store programsnetworks etc.UNIXAPIsystemdaemonsuserapplicationsX1/7/2008 cs3320 14● When a program is executed, it is loaded into memory. It is called a process when it is executing.● Most processes read/write data from/to files● Processes and files have an owner● UNIX supports hierarchical directory structure● Files and processes have a location within the directory structure● UNIX provides the capabilities to create, modify and destroy files, programs, and processes.Process1/7/2008 cs3320 15● Sharing of resources: CPU (time slices), memory (pages), disk (blocks)● Communication: process-device controller, process-process, etc. (pipes 1-way, sockets 2-way)● Utilities: Unix comes with a large collection of utilities; we will study many of these.● Programmer support: All kinds of compilers available; Access to parallel processing, file handling and interprocess communication via System calls in CUnix Attributes1/7/2008 cs3320 16Advantages of UNIX• It is multitasking, therefore, multiple programs can run at one time. • It is multiuser, allowing more than a single user to work at any given time. This is accomplished by sharing processing time between each user and utilizing distributed computing systems. • It is safe, preventing one program from accessing memory or storage space allocated to another, and enables protection, requiring users to have permission to perform certain functions, i.e. accessing a directory, file, or disk drive1/7/2008 cs3320 171/7/2008 cs3320 18Two Main Varieties of Unix•System V (AT&T) and •BSD (Berkeley Standard Distribution)• Both are merged now. SunOS, IRIX, AIX, HP-UX have features from both varieties although most are System V Unix.•Other Unix versions you may have heard of:● Linux (Fedora, Red Hat, Ubuntu, SUSE, etc.)● Sun Java Desktop OS, Solaris● Apple OS/X1/7/2008 cs3320 19Sub-Varieties of Unix•Linux (Runs on PC architecture)● Fedora● Red Hat● Ubuntu● Sun Java Desktop OS, etc.•Sun Solaris (Runs on SPARC architecture)•Apple OS/X (Runs on PowerPC and Intel platforms)1/7/2008 cs3320 20Philosophies of Unix• Pipe mechanism● Output of one process can be used as input for another process. e.g.• $ who | sort● Using the pipe mechanism, complex tasks can be broken down into simpler ones and combined using pipes etc.• Super user ● user who has complete control over the system resources. Typically the System's Administrator.1/7/2008 cs3320 21Review• Computer Systems• Unix as an operating system• Processes • Unix Attributes• Unix Varieties • Unix