GTECH 201

1. GTECH 201 Lecture 02The computing environmentin the geography department

2. Technical Prelims • Data versus programs • Operating systems • Maneuvering the Windows desktop • Files and directories • Networks and the Internet

3. Data on a Computer • Data is a gathered body of observations • To use on a computer, data has to be translated into binarydigital form

4. Computer • Takes data and manipulates it for some result based on a program or sequence of instructions on how the data is to be processed • Computers usually include the means for storing data (including the program, which is also a form of data)

5. Digital • Describes electronic technology that processes data in terms of two states: • Positive = 1 • Non-positive = 0 • Data is expressed as a string of 0's and 1's • Each of these state digits is referred to as a bit

6. Binary and Hexa-decimal • Power of 2 (instead of power of 10) • Decimal = 21Binary = 10101 • The numbers 0-15 in decimal, binary, and hexa-decimal notation:

7. Program • A program is a specific set of ordered operations for a computer to perform • It is special kind of data that tells a computer how to operate on user data • Interactive (user-driven) programs • Batch programs, scripts

8. Programming • When you write a program, you do so in a formalized way that is still readable for humans • It then has to be translated into binary form to be executed by the computer • Examples for programming languages: • Fortran • Java • C# • Perl • Python • Visual Basic

9. Operating System (“OS”) • The program that manages all the other programs in a computer • The other programs are called applications or application programs • In addition, it provides the following services: • It manages the sharing of internal memory among multiple applications ..continued on next slide

10. OS continued • It handles input and output to and from hard disks and printers • It sends messages to each application or interactive user about the status of operation and any errors that may have occurred • In a multitasking operating system, where multiple programs can be running at the same time, the operating system determines which applications should run in what order and how much time should be allowed for each application before giving another application a turn

11. OS Examples • Windows 98, NT, XP • Linux, Unix, AIX, SunOS • Apple Macintosh OS 9, or OS 10 • Palm OS, Windows CE • OS/400 • MVS

12. Multi-user / Multi-tasking • Windows is a multi-tasking OSallowing one user to perform more than one computer task at a time • E.g., when you open your Web browser and then open word at the same time • Linux is a multi-user OSallowing several people to share the computer’s resources at the same time

13. Multi-user OS • Each user has an account • Has a home (personal space on some hard disk) • Has privileges (and constraints) • What programs can be run • How much disk space is allotted • Has a login consisting of • User name (account name) • Password

14. Differences betweenWindows and Unix • Windows XP allows many users but only one at a time • That one user has sole access to all computer resources (within the limits of the privileges of the account) • In Unix, monitor, mouse and keyboard form a terminal that is usually (but not necessarily) used by only one user • Other resources, e.g. hard disk or memory are shared between users

15. Computer Resources • Monitor – screen size, resolution • Keyboard and mouse • Memory – volatile, measured in MBytes • Hard disk(s) – permanent, GBytes • Diskette, CD-ROM, DVD drives • Graphics card, network card • Printer(s) • USB (Firewire, Bluetooth) devices

16. Windows Desktop

17. Windows Desktop • Desktop icons • Start menu • Quick launch icons • User data vs. application programs

18. Start Menu

19. All Programs

20. What is a File? • Everything • An entity of data that is capable of being manipulated as an entity (for example, moved from one file directory to another) • Must have a unique name within its own directory • Name suffix describes a given format or use • For example, a program or executable file is sometimes given or required to have an ".exe" suffix

21. ASCII • American Standard Code for Information Interchange • The most common format for text files in computers and on the Internet • Each alphabetic, numeric, or special character is represented with a 7-bit binary number • 128 possible characters are defined

22. Binary File • A file whose content must be interpreted by a program that understands exactly how it is formatted • The file is not in any externally identifiable format so that any program that wanted to could look for certain data at a certain place within the file • A program has to know exactly how the data inside the file is laid out to make use of the file

23. Directory • In MS Windows, a folder is a named collection of related files that can be retrieved, moved, and otherwise manipulated as one entity • The folder and file terms were chosen to be consistent with the metaphor that the user interface is a desktop • In some other operating systems, such as DOS, or most Unix-based operating systems, the term directory is used rather than folder

24. Directories and Drives • In Windows, a way to organize data on a large hard disk

25. Directory Structure

26. Directory Paths • Hierarchical directory structure • From root of directory tree to chosen leaf • In Windows: C:\My Documents\GTECH201\week01 • In Unix: /courses/GTECH201/week01 • .. signifies parent directory

27. File Sizes • Bit 0 or 1 = 2 states • Byte 8 bit = 256 (28) states • Kilobyte 1024 (210) Bytes (typical page) • Megabyte 1024 Kilobytes (short novel) • Gigabyte 1024 Megabytes (Great Books) • Terabyte 1024 Gigabytes (large library)

28. File Permissions (Unix) • Three categories of file users • owner • Three types of access • read • All three can be encoded in one octal number with r=4, w=2 and x=1 • 755 means owner can do everything, while group and world can read and execute • 644 means owner can read and write, while all others can only read the file • group • world • write • execute

29. Networks • Computers and other devices interconnected by communication paths • Networks can interconnect with other networks and contain sub-networks • A local area network (LAN) is a group of computers and associated devices that share the resources of a single processor or server within a small geographic area (e.g., within a building)

30. Mapping Network Drives

31. Internet • Network of networks in which users at any one computer can get information from any other connected computer • Backbone for email and the WWW • The WWW is the universe of network-accessible information accessible through the Hypertext Transfer Protocol

32. Internet Names and Numbers • Internet addresses need to be unique • Internet Protocol (IP) address is a dotted quad notation of decimal numbers representing 8 bits • 146.95.2.10 (easily readable by computers) • Domain names (geo.hunter.cuny.edu) are assigned hierarchically and read right-to-left • .edu, .com, .org are top-level domains • cuny, amazon, microsoft are 2nd-level domains

33. Email • The exchange of computer-stored messages over a network (of networks) • Usually in ASCII, although binary attachments (ÐÏࡱá) are allowed • Messages are sent to a person’s email address or an email reflector • Email address: jochen@hunter.cuny.edu • Reflector: geoall@geo.hunter.cuny.edu

34. Creating Web Pages • Your website • Accessing files on your website • File permissions • chmod 644 and 755 /data/moon/array2/aa/fbaggins/public_html/index.html www.geo.hunter.cuny.edu/~fbaggins/Lab02/Lab02.html