1. Review

2. Secondary Memory Devices
devices provide
long-term storage
Information is moved
between main memory
and secondary memory
as needed
Central
Processing
Unit
Main
Memory
Hard disks
Floppy disks
ZIP disks
Writable CDs
Writable DVDs
Tapes
Floppy Disk
Hard Disk

3. A Computer Specification
Consider the following specification for a personal computer:
2.8 GHz Pentium 4 Processor
512 MB RAM
80 GB Hard Disk
48x CD-RW / DVD-ROM Combo Drive
17” Video Display with 1280 x 1024 resolution
56 Kb/s Modem
What does it all mean?

4. Software Categories Operating System Application program
controls all machine activities
provides the user interface to the computer
manages resources such as the CPU and memory
Windows XP, Unix, Linux, Mac OS
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)

5. Memory
Main memory is divided into many memory locations (or cells)
9278
9279
9280
9281
9282
9283
9284
9285
9286
Each memory cell has a numeric address, which uniquely identifies it
Remember this?

6. Storage Capacity
Every memory device has a storage capacity, indicating the number of bytes it can hold
Capacities are expressed in various units:
Unit Symbol Number of Bytes
kilobyte
megabyte
gigabyte
terabyte
KB 210 = 1024
MB 220 (over 1 million)
GB 230 (over 1 billion)
TB 240 (over 1 trillion)

7. Bit Combinations Each combination can represent a particular item
There are 2N combinations of N bits
Therefore, N bits are needed to represent 2N unique items
1 bit ?
2 bits ?
3 bits ?
4 bits ?
5 bits ?
How many
items can be
represented by
21 = 2 items
22 = 4 items
23 = 8 items
24 = 16 items
25 = 32 items

8. The Central Processing Unit (CPU)
A CPU is on a chip called a microprocessor
It continuously follows the fetch-decode-execute cycle:
fetch
Retrieve an instruction from main memory
decode
Determine what the
instruction is
execute
Carry out the
instruction

9. The Central Processing Unit
The CPU contains:
Performs calculations and makes decisions
Arithmetic / Logic Unit
Coordinates processing steps
Control Unit
Small storage areas
Registers

10. The Internet: Then and Now
The Internet was created by the Advanced Research Projects Agency (ARPA) and the U.S. Department of Defense for scientific and military communications.
The Internet is a network of interconnected networks. Even if part of its infrastructure was destroyed, data could flow through the remaining networks.
The Internet uses high-speed data lines, called backbones, to carry data. Smaller networks connect to the backbone, enabling any user on any network to exchange data with any other user.
ARPANET, NSFnet, Internet
Internetworking: the process of connecting separate networks

12. How the Internet Works - TCP/IP
Every computer and network on the Internet uses the same protocols (rules and procedures) to control timing and data format.
The protocol used by the Internet is the Transmission Control Protocol/Internet Protocol, or TCP/IP.
No matter what type of computer system you connect to the Internet, if it uses TCP/IP, it can exchange data with any other type of computer.

13. How the Internet Works - Routing Traffic Across the Internet
Most computers don't connect directly to the Internet. Instead, they connect to a smaller network that is connected to the Internet backbone.
The Internet includes thousands of host computers (servers), which provide data and services as requested by client systems.
When you use the Internet, your PC (a client) requests data from a host system. The request and data are broken into packets and travel across multiple networks before being reassembled at their destination.

14. How the Internet Works - Addressing Schemes
In order to communicate across the Internet, a computer must have a unique address.
Every computer on the Internet has a unique numeric identifier, called an Internet Protocol (IP) address.
Each IP address has four parts – each part a number between 0 and 255. An IP address might look like this:

15. Application Protocols Transmission Control Protocol Layer
LayerComments
Application Protocols
LayerProtocols specific to applications such as WWW, , FTP, etc.
Transmission Control Protocol Layer
TCP directs packets to a specific application on a computer using a port number.
Internet Protocol Layer
IP directs packets to a specific computer using an IP address.
Hardware Layer
Converts binary packet data to network signals and back. (E.g. ethernet network card, modem for phone lines, etc.)

16. How the Internet Works - Domains and Subdomains
In addition to an IP address, most Internet hosts or servers have a Domain Name System (DNS) address, which uses words.
A domain name identifies the type of institution that owns the computer. An Internet server owned by IBM might have the domain name ibm.com.
Some enterprises have multiple servers, and identify them with subdomains, such as products.ibm.com.

18. Major Features of the Internet - The World Wide Web
The World Wide Web is a part of the Internet, which supports hypertext documents, allowing users to view and navigate different types of data.
A Web page is a document encoded with hypertext markup language (HTML) tags.
HTML allows designers to link content together via hyperlinks.
Every Web page has an address, a Uniform Resource Locator (URL).

19. Major Features of the Internet - File Transfer Protocol (FTP)
File transfer protocol (FTP) is the Internet tool used to copy files from one computer to another.
Using a special FTP program or a Web browser, you can log into an FTP host computer over the Internet and copy files onto your computer.
FTP is handy for finding and copying software files, articles, and other types of data. Universities and software companies use FTP servers to provide visitors with access to data.

20. Major Features of the Internet - Telnet
Telnet is a specialized service that lets you use one computer to access the contents of another computer – a Telnet host.
A Telnet program creates a "window" into the host so you can access files, issue commands, and exchange data.
Telnet is widely used by libraries, to allow visitors to look up information, find articles, and so on.

22. What Firewall Software Does
A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through.

23. How Firewalls Work
Firewalls use one or more of three methods to control traffic flowing in and out of the network:
Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded.
Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa.
Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.

24. Firewall filters
Firewall Configuration: Firewalls are customizable. This means that you can add or remove filters based on several conditions. Some of these are:
IP addresses - A typical IP address looks like this: For example, if a certain IP address outside the company is reading too many files from a server, the firewall can block all traffic to or from that IP address.
Domain names -. A company might block all access to certain domain names, or allow access only to specific domain names.
Protocols - The protocol is the pre-defined way that someone who wants to use a service talks with that service. The http in the Web's protocol. Some common protocols that you can set firewall filters for include (next slide):
Ports - Any server machine makes its services available to the Internet using numberedports, one for each service that is available on the server. For example, if a server machine is running a Web (HTTP) server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. A company might block port 21 access on all machines but one inside the company.
Specific words and phrases - This can be anything. The firewall will sniff (search through) each packet of information for an exact match of the text listed in the filter.

25. Types And Sources Of Network Threats
Denial-of-Service
Unauthorized Access
Confidentiality Breaches
Destructive Behavior

26. Acronyms you need to know
IP (Internet Protocol) - the main delivery system for information over the Internet
TCP (Transmission Control Protocol) - used to break apart and rebuild information that travels over the Internet
HTTP (Hyper Text Transfer Protocol) - used for Web pages
FTP (File Transfer Protocol) - used to download and upload files
HTML (Hypertext Markup Language) - used to send text-based information ( )
URL – (Uniform Resource Locator)- an address that identifies a particular file on the Internet, usually consisting of the protocol, as http, followed by the domain name.

27. Acronyms you need to know
GUI-
RAM-
ROM
DVD CD
CPU
ALU
OS-
I/O-

28. Acronyms you need to know
GUI- Graphic User Interface
RAM-Random Access Memory
ROM- Read Only Memory
DVD- Digital Versatile Disk
CD- Compact Disc
CPU- Central Processing Unit
ALU- Arithmetic Logic Unit
OS- Operating System
I/O- Input/Output