GTECH 201

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GTECH 201

• Lecture 02The computing environmentin the
  geography department

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Technical Prelims

• Data versus programs
• Operating systems
• Maneuvering the Windows desktop
• Files and directories
• Networks and the Internet

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Data on a Computer

• Data is a gathered body of observations
• To use on a computer, data has to be translated
  into binary digital form

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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)

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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

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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

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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

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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

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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
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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

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OS Examples

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

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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 computers resources at the same time

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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

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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

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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

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Windows Desktop
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Windows Desktop

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

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Start Menu
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All Programs
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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

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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

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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

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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

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Directories and Drives

• In Windows, a way to organize data on a large
  hard disk

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Directory Structure
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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

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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)

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File Permissions (Unix)

• Three categories of file users
• owner
• Three types of access
• read
• All three can be encoded in one octal number with
  r4, w2 and x1
• 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

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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)

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Mapping Network Drives
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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

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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

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Email

• The exchange of computer-stored messages over a
  network (of networks)
• Usually in ASCII, although binary attachments
  (ÐÏàá) are allowed
• Messages are sent to a persons email address or
  an email reflector
• Email address jochen_at_hunter.cuny.edu
• Reflector geoall_at_geo.hunter.cuny.edu

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Creating Web Pages

• Your website
• Accessing files on your website
• File permissions
• chmod 644 and 755

/data/moon/array2/aa/fbaggins/public_html/index.ht
ml
www.geo.hunter.cuny.edu/fbaggins/Lab02/Lab02.html