Java Software Solutions

1. Java Software Solutions Chapter 1.1 Computer Systems

2. 1. Computer Processing • A computer system is made up of hardware and software. • Hardware: Chips, keyboards, disks, wires, etc. • Software: Programs and the data those programs use. • Key Components of a Computer System • central processing unit (CPU) • input/output (I/O) devices • main memory • secondary memory devices

3. Memory • Programs and data are held in storage devices called memory, which fall into two categories: • Main Memory (“primary memory,” “central memory”…) • The storage device (e.g., chips on the mother board) that holds the programs and their data (software) while the programs are executing. • Secondary Memory • Devices such as hard disks that store software in a relatively permanent manner. • We save our software on secondary memory. Copies of the software are brought into main memory when we execute our programs. • Copies = data and programs

4. Software Categories • We will be concerned with two categories of software. • The operating system. • Provides a user interface that allows us to interact with the machine (enter input and view output). • Manages computer resources such as the CPU and main memory. • Provides protection, and much more. • Application Software • Generic term for just about any software other than the operating system. • Word processors, spreadsheets (office tools), web browsers, games, hosts of search engines, twitter, facebook, …etc. • Scientific applications; business / commercial applications… • The focus of this course is development of high-quality application programs to be used in business / commercial applications.

5. What This Means to Us • We will be learning to create application programs using the Java programming language. • We will be using an IDE called NetBeans. • Current version of NetBeans is 6.7 but 5.0 and 5.5 should both be sufficient also. • IDE stands for IntegratedDevelopmentEnvironment. (Know this) • There are many IDEs ‘out there.’

6. More: What this means to us • You will download and install the J2SE Standard Edition and Development Kit JDK and NetBeans 6.7 (bundled together) from links on my web page. • See: Link to Download NetBean and Java. • See the link on my web page and instructions to download and install NetBeans 6.7 and the Java JDK. • See NetBeans Tutorial and Project0 Details are here. • See also the tutorial on how to use NetBeans 6.7 to develop and submit Project0.

7. Analog versus Digital Signals • Analog information and/or signals are continuous, varying in direct proportion to the source of the information – like the amplitude of a wave may vary with volume. It’s period may vary with frequency… • (Hz (frequency) measured in cycles per second; Period is seconds per cycle) • Digital technology breaks information into discrete pieces and represents the pieces as numbers. • Music on a CD is stored digitally, as a series of numbers. The music is sampled about 40,000 times per second and each number represents the voltage level of one specific instance of the recording.

8. An Analog Signal versus a Digital Signal 1 0 1 0 0 1 … digital analog

9. Binary Numbers • A digital computer stores information as numbers: ones and zeroes. • These numbers represent ‘state’ • On/off; one/zero, etc. • All information in a computer is stored and managed as binary values. • The binary number system has only two digits, 0 and 1. • A single binary digit is called a bit.

10. Converting Binary Numbers to Decimal Numbers • Starting with the rightmost bit in a binary number, each position represents a power of 2, with the rightmost bit position representing 20which is decimal 1, the next bit position representing 21which is 2 and the next representing 22 which is 4, etc. • Binary 1011 is 1* 23 or 8 + 0 * 22 or 0 +1 * 21 or 2 + 1 * 20 or 1 which adds up to 11 decimal (base 10). • Binary 11001001 is 201 decimal. • CAN YOU DO THIS???? Yes, you need to know this! • In general, n bits can represent 2nunique items. • Computers typically manipulate sequences of 8 bits with each sequence of 8 bits referred to as a byte.

11. 2. Hardware Components • We use the term computer architecture to describe how the hardware components of a computer are put together. • A program and its data reside in main memorywhile the program runs. • The Central Processing Units (CPU) reads one program instruction from main memory and executes it. • (Called ‘fetch – execute’ cycle) • If an instruction needs data, such as the amount in a bank account, the CPU will acquire that information from central memory (which may require the access of data in secondary memory to be brought into memory first). • The process repeats until the program ends.

12. Peripherals • Almost all devices in a computer other than the CPU and main memory are called peripherals. • Controllersare devices that coordinate the activities of specific peripherals. • A unit with several disks attached will have a disk controller for timing, contention, data access, … • Input/Output (I/O) devices like disks and other secondary memory devices (Jump drives, etc.)are considered peripherals. • We won’t pay much attention to them.

13. Input/Output Devices • For our purposes, the primary I/O devices will be the keyboard and the monitor. • Output on a monitor is achieved by breaking the screen picture into small pieces called pictureelements (pixels). • The pixels are represented in the computer as numbers (as is everything else) and each pixel has a specific ‘screen address.’ • A typical monitor can display a number of ‘screenresolutions’ such as 640x480, 800x720, 1280 x 1024 and others… • These numbers represent the number of pixels used to display the screen information. • Aspect ratio

14. Main Memory and Secondary Memory • Main memory is made up of a series of consecutive memory locations called addresses. • Associated with each memory location is a uniqueaddress. • On many computers, each memory location consists of 8 bits, or one byte of information. • The storage capacity of a device such as main memory is the total number of bytes it can hold. • A kilobyte (KB) is 1,024 bytes or 210 bytes. • Larger units are a megabyte (MB), a gigabyte (GB), and a terabyte (TB). • It is usually easier to think about these capacities by rounding them off.

15. Characteristics of Main Memory • When data is stored in a main memory location, it overwrites (thus destroying) any information that was previously stored there. • Main memory is said to be volatile. • The information stored in it will be lost if its power is lost. (meaning of volatile in this context) • You should frequently save your work onto a secondary memory device (such as a disk).

16. Secondary Memory Devices • A disk is a direct access (also called random access) device since the read/write head moves quickly to the information needed. • In the prerequisite to this course, you have seen pictures of disks and how they operate. • Disk is both a direct access device and can be accessed sequentially just like a tape unit. • A tape must be sequentially processed / rewound / or fast-forwarded to get to the desired information. • A tape is thus a considered a sequential access device. • While tapes were the medium of choice when disks were expensive and access was controlled to those types of applications really needing disks, tapes now are almost exclusively used for backup storage. • Very inexpensive and can store huge quantities of data – often archival.

17. Two More Terms • Random Access Memory (RAM) • The terms RAM and main memory are basically interchangeable. Sometimes called primary memory. • RAM should probably be called read-write memory since data can be both written to it and read from it. • Read-Only Memory (ROM) • After information is stored on ROM, it cannot be altered (easily). Data in ROM is ‘burned’ into the chips • Can sometimes be reprogrammed (PROMs) and sometimes we have Erasable Programmable Read Only Memories (EPROMs) (Need special equipment) • ROM chips are often embedded into the main circuit board to provide the preliminary instructions when the computer is initially turned on.

18. Other Memory Devices • Additional memory devices include CD-ROM, CD-Recordable (CD-R) drives, CD Rewritable (CD-RW) discs, DVD devices, jump drives, …. • (Know the differences) • The speed of a CD drive is expressed in multiples of X, which represents a data transfer speed of 153,600 bytes per second. • Due to improvements in technology, storage capacity approximately doubles every 18 months.

19. Central Processing Unit • The ‘processor’ interprets and executes your program’s instructions one at a time – sequentially. • Consists of the arithmetic and logic unit, the control unit, and the registers (usually in the ALU and Control Units) • Registers store bits (16-bit registers; 32-bit registers, …) • Control Unit dissects the instruction and directs the ALU to perform the calculations / comparisons using the registers. • CPU has other registers too: • Instruction register; program counter, more

20. CPU - more • The notion of a stored-program computer – a von Neumann machine – stored both program instructions and data together in main memory. • Fetch-decode-execute cycle • Fetch instruction from primary memory (RAM) • Decode instruction (to see what it is to be done) • Execute the instruction using registers • Repeat

21. CPU - more • CPU on a chip called a microprocessor • Circuit board also contains communications sockets, etc. for connection with video displays, etc. • Main circuit board also contains the system clock which pulses. • Instructions are in synch with these pulses • Some take a single pulse; others, more. • Often called clock speed. • All activities in a computer and controlled by the clock with something we call ‘clock cycles.’ • We may say that an instruction executes in two clock cycles.

22. 3. Networks • A network is two or more computers connected together to exchange information. • Each computer of a network has a network address. • One technique to improve network speed is to divide large messages into segments, called packets. • Packets have fixed formats and other constraints… • Then send the individual packets across the network intermixed with pieces of other messages sent by other users.

23. Local Area Networks and Wide Area Networks • A Local-Area Network (LAN) is designed to span short distances and connect a relatively small number of computers. • Within a building or small area • You may connect to the LAN here in this classroom and see these slides/ take notes on them, etc. • A Wide-Area Network (WAN) connects two or more LANs, often across long distances. • LANs connected by a WAN are often owned by different companies or organizations, and might be located in different countries. • Generally, one computer takes care of communications.

24. The Internet • The Internet is a network of networks. • Grew out of U.S Government ARPA (and ARPAnet) • In 2000, number of computers connected to Internet = 10 million. • A protocol is a set of rules that governs how two things communicate. • The software that controls the movement of messages across the Internet must conform to a set of protocols called TCP/IP for Transmission Control Protocol/Internet Protocol. • IP defines how information is formatted and transferred • TCP software handles the transmission and reconstituting of messages, error control, etc. (contention, …) • Have layers of communications and different protocols… • Every computer connected to the Internet has an IPaddress that uniquely identifies it among all other computers on the Internet.

25. IP Address vs Internet Address • An IP address is of the form 204.192.116.2. • Fortunately, Internet allows each computer to be given aunique name - often referred to as its Internet Address. • The first part of an Internet Address is the local name of a specific computer. • The rest of the name is the domain name. • Ours is: osprey.unf.edu. • Osprey is local name • unf.edu is the domain name. • Can have ‘subdomains’ within domain for departments, etc. • Last part of domain name is the ‘top level domain name’. • Some are: .edu .com, .org, .mil …

26. The Domain Name System • The Internet uses another software program, the Domain Name System (DNS) to translate an Internet Name (osprey.unf.edu) to a corresponding IP Address (139.62.37.20). • Each organization connected to the Internet operates a domain server that maintains a list of all its computers and their IP addresses. • Used for mapping.

27. The World Wide Web • The World Wide Web (also known as WWW or the Web) makes the exchange of information easy. • Web software provides a common interface through which many different types of information can be accessed with a mouse click. • Web: based on concepts of hypertext & hypermedia. • Hypertext – based on links to support jumping as needed. To manage large amounts of information. Basically used to originally link ‘documents.’ • Hypermedia incorporates graphics, sound, animations, and video.

28. Hypertext and Browsers • Web Server: computer dedicated to providing access to Web documents. • Web documents are written in a variety of languages now. Originally, there was just html. Now there are many with many variations… • Browsers load / interpret documents provided by a Web server. • Many documents are formatted using the HyperText Markup Language (HTML). • Links to Java programs can be embedded in html documents and executed through Web browsers.

29. Uniform Resource Locators • Information on the Web is found by identifying a Uniform Resource Locator (URL) • A URL uniquely specifies documents and other information for a browser to obtain and display. • An example URL is http://www.unf.edu • We sometimes now just say, web address… • URL: • First piece of URL is the protocol (HyperText Transfer Protocol –HTTPin this example) which determines the way the browser should communicate. • The second piece is the Internet address of the machine on which the document is stored. • A typical third piece of information is the file name of the file you wish to view. • Default third piece: index.html

30. Another Sample URL • http://www.unf.edu/~broggio/Fall2009.html • In this URL, the protocol is http (HyperText Transfer Protocol). • Machine referenced is www (web server found at unf.edu) • Information is stored in a ‘file’ in my home directory named Fall2009.html (programmed in html) • www.unf.edu/~broggio by itself, refers to an index.html file stored in a directory, broggio, within some UNF web server • The Internet vs the World Wide Web • The Internet makes it possible to communicate via computers around the world. • Internet IS a network; Communications… • The Web makes that communication a straightforward and enjoyable activity via software. • The Web can be used on a LAN or even a single machine that is not connected to any network. • Information service based on a set of software applications

31. The Internet • A global network connecting millions of computers. Hundreds of countries are linked into exchanges of data, news and opinions. • Unlike online services, which are centrally controlled, the Internet is decentralized by design. • Each Internet computer, called a host, is independent. Its operators can choose which Internet services to use and which localservices to make available to the global Internet community. • Remarkably, this anarchy by design works exceedingly well. • There are a variety of ways to access the Internet. Most online services offer access to some Internet services. • Internet Service Providers (ISP): Comcast, AOL, etc. • The Internet is notsynonymous with World Wide Web.

32. World Wide Web A system of Internetservers that supportspeciallyformatteddocuments. • The documents are formatted in a markup language called HTML (HyperText Markup Language) and a host of other languages that support links to other documents, as well as graphics, audio, and video files. • This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web. • There are several applications called Web browsers that make it easy to access the World Wide Web; Four of the most popular being Netscape Navigator, Microsoft's Internet Explorer, MozillaFirefox, Safari, and others. • World Wide Web is not synonymous with the Internet.

33. Programming • The rest of this course explores the process of designing and developing programs using an object-oriented language. Ours is Java. • All of the software we have discussed including the Internet and Web protocols are simply (but not simple) programs some programmer has written. • Next section discusses the purpose of programming in general and introduces the Java Programming Language.