Transcript Lecture 02 - Hunter College, Department of Geography

GTECH 201
Lecture 02
The computing environment
in the geography department
Technical Prelims
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Data versus programs
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Operating systems
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Maneuvering the Windows desktop
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Files and directories
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Networks and the Internet
Data on a Computer
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Data is a gathered body of observations
To use on a computer, data has to be
translated into binary digital form
Computer
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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)
Digital
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Describes electronic technology that
processes data in terms of two states:
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Positive = 1
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Non-positive = 0
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Data is expressed as a string of 0's and 1's
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Each of these state digits is referred to as a
bit
Binary and Hexa-decimal
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Power of 2 (instead of power of 10)
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Decimal = 21
Binary = 10101
64
32
16
8
4
2
1
0
0
1
0
1
0
1
The numbers 0-15 in decimal, binary,
and hexa-decimal notation:
0
1
2
3
4
5
6
7
0
1
10
11
100
101
110
111
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1000 1001 1010 1011 1100 1101 1110 1111
8
9
A
B
C
D
E
F
Program
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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
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Interactive (user-driven) programs
Batch programs, scripts
Programming
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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:
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Fortran
Java
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C#
Perl
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Python
Visual Basic
Operating System (“OS”)
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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:
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It manages the sharing of internal memory
among multiple applications
..continued on next slide
OS continued
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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
OS Examples
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Windows 98, NT, XP
Linux, Unix, AIX, SunOS
Apple Macintosh OS 9, or OS 10
Palm OS, Windows CE
OS/400
MVS
Multi-user / Multi-tasking
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Windows is a multi-tasking OS
allowing one user to perform more than
one computer task at a time
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E.g., when you open your Web browser
and then open word at the same time
Linux is a multi-user OS
allowing several people to share the
computer’s resources at the same time
Multi-user OS
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Each user has an account
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Has a home (personal space on some hard
disk)
Has privileges (and constraints)
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What programs can be run
How much disk space is allotted
Has a login consisting of
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User name (account name)
Password
Differences between
Windows and Unix
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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
Computer Resources
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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
Windows Desktop
Windows Desktop
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Desktop icons
Start menu
Quick launch icons
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User data vs. application programs
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Start Menu
All Programs
What is a File?
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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
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For example, a program or executable file is
sometimes given or required to have an ".exe"
suffix
ASCII
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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
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128 possible characters are defined
Binary File
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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
Directory
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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
Directories and Drives
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In Windows, a way to organize data on
a large hard disk
Directory Structure
Directory Paths
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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
File Sizes
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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)
File Permissions (Unix)
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Three categories of file users
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group
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world
Three types of access
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owner
 write
 execute
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
Networks
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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)
Mapping Network Drives
Internet
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Network of networks in which users at
any one computer can get information
from any other connected computer
Backbone for email and the WWW
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The WWW is the universe of networkaccessible information accessible through
the Hypertext Transfer Protocol
Internet Names and Numbers
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Internet addresses need to be unique
Internet Protocol (IP) address is a dotted
quad notation of decimal numbers
representing 8 bits
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146.95.2.10 (easily readable by computers)
Domain names (geo.hunter.cuny.edu) are
assigned hierarchically and read right-to-left
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.edu, .com, .org are top-level domains
cuny, amazon, microsoft are 2nd-level domains
Email
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The exchange of computer-stored
messages over a network (of networks)
Usually in ASCII, although binary
attachments (ÐÏ à¡± á) are allowed
Messages are sent to a person’s email
address or an email reflector
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Email address: [email protected]
Reflector: [email protected]
Creating Web Pages
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Your website
/data/moon/array2/aa/fbaggins/public_html/index.html
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Accessing files on your website
www.geo.hunter.cuny.edu/~fbaggins/Lab02/Lab02.html
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File permissions
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chmod 644 and 755