Review

1. Review

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

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 • 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. 9278 9279 9280 9281 9282 9283 9284 9285 9286 Main memory is divided into many memory locations (or cells) Each memory cell has a numeric address, which uniquely identifies it Memory 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 KB 210 = 1024 kilobyte megabyte gigabyte terabyte MB 220 (over 1 million) GB 230 (over 1 billion) TB 240 (over 1 trillion)

7. 1 bit ? 2 bits ? 3 bits ? 4 bits ? 5 bits ? How many items can be represented by 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 21 = 2 items 22 = 4 items 23 = 8 items 24 = 16 items 25 = 32 items

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

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: 205.46.117.104.

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: 216.27.61.137. 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 (e-mail) • 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