Barrons Publishing Dictionary of Computer and Internet Terms 10th

POWER SUPPLY.

The watt and ampere ratings of a power supply represent the maximum that it can deliver; the actual power consumed will depend on the devices attached to it. Correct practice is to use a power supply with the correct voltages and correct or higher watt and ampere ratings.

PowerPC a family of high-performance 32and 64-bit microprocessors developed jointly by IBM, Motorola, and Apple to compete with the Intel microprocessors and Microsoft software that were dominating the market. From 1994 to 2006, PowerPC CPUs were used in the Apple Macintosh. Despite the name, the PowerPC microprocessor has never been used in Windows-based PCs.

PowerPoint presentation software sold with Microsoft’s Office suite. The user can create an outline version of a talk and then display it one page at a time or one line at a time, and graphics can be included as well. Speaker notes or handouts can also be printed. See PRESENTATION GRAPHICS.

PowerToys a set of small Windows utilities distributed free of charge by Microsoft to allow additional customization of the operating system.

PPM (pages per minute) a measure of the speed of a printer.

PPP (Point-to-Point Protocol) a communications protocol often used in

DIAL-UP NETWORKING. Compare SLIP. See PROTOCOL.

PPPoE (Point to Point Protocol over Ethernet) a protocol allowing the use of PPP (as would be used in dial-up networking) when the user is connected to the network through an Ethernet port (as would be the case for a user connected to the Internet via a cable modem).

precedence the property of arithmetic operations that determines which operations are done first in a complex expression.

Typically, exponentiations are done first, then multiplications and divisions, and finally additions and subtractions. For example, the Excel expression

=5+4*3^2

means 5 + 4 × 9 = 5 + 36 = 41. You can use parentheses to change the order of the operations when you need to, since any operation in parentheses will be done first. For example,

=5+(4*3)^2

means 5 + 122 =5 + 144 = 149.

precision the exactness with which a quantity is specified. For numbers, the precision is the number of significant digits that the computer keeps track of when it carries out arithmetic operations. See ROUNDING ERROR. For examples in Java, see DOUBLE PRECISION; LONG.

pretzel (slang) nickname for , the Macintosh command key.

preview a viewing mode that displays the appearance of the finished document or drawing. In order to let you work quickly, many drawing programs show you only an outline of the objects on screen. (This is called WIREFRAME mode.) When you want to see what the final printed piece would look like, you have to use the “Preview” command. Then all of the objects appear with their fills so that you can check whether they are layered correctly.

Most drawing programs will allow you to work in preview mode, but the time spent redrawing the screen after each action can be quite irritating. If it becomes a problem, work in the wireframe view and preview frequently to check your work. Another method is to open two windows containing the same file, one in wireframe and the second in preview.

Most word processors also allow you to preview your document.

primary key a field in a database record with a unique identifier. When sorting a database, the items will be sorted first according to the primary key. Sometimes you also wish to define a secondary key. For example, you may wish to sort a list of club members first by their membership date (the primary key), and then alphabetically by their last name (the secondary key).

primary mouse button the button used to select objects on a mouse with more than one button. For a right-handed user, this is usually the left mouse button. The SECONDARY MOUSE BUTTON is the button used to call up the action menu.

Left-handed users have the option of reversing the default order for mouse buttons; they can use the right mouse button as the primary button and the left button as the secondary.

primitive a basic element or concept in terms of which larger elements or concepts are formed. For example, in programming languages such as FORTH and Lisp, it is common for programmers to create their own statements by defining them in terms of primitives provided by the language.

print head

1.The part of an INKJET PRINTER that actually contacts the paper in order to print. It contains tiny holes through which ink is sprayed; if some of these holes are clogged, printing will be streaky and the print head should be cleaned as specified in the instructions.

2.The part of an IMPACT PRINTER that presses on the ribbon, which contacts the paper.

print server a computer through which other computers access a printer over a network. A print server may be an ordinary computer or a small circuit board or box mounted inside or just outside the printer.

print spooler a program that stores computer output in memory so that the user’s program can finish creating the output without waiting for the

program a set of instructions for a computer to execute. A program can be written in a programming language, such as C or Java, or in an assembly language. See APPLICATION PROGRAM; UTILITY.

programmable function key a key on a computer keyboard whose function depends on the software being run. In many cases, programmable function (PF) keys can be defined as equivalent to combinations or sequences of other keys.

programmatically (adverb) by means of a computer program. For example, in Windows, the volume level of the speaker can be changed programmatically; that is, software can change it.

programmer a person who prepares instructions for computers.

programming the process of composing instructions for a computer to carry out. A programmer needs to develop a well-defined concept of how to solve a problem. (See ALGORITHM.) Then this concept must be translated into a computer language. (See PROGRAMMING LANGUAGE.) Finally, the program needs to be typed into the computer, tested, and debugged before being placed into service.

programming language a language used to give instructions to computers. During the 1960s and 1970s, a huge variety of programming languages were developed, most of which are no longer in wide use. Moreover, a substantial amount of programming is now done with special program development tools (e.g., Visual Basic), or in programming languages that pertain to specific pieces of software (e.g., Maple) rather than by simply writing instructions in a general-purpose language.

The following is a rough classification of programming languages. Most of these languages are treated in separate articles in this book.

1.General-purpose languages for large, complex programs: PL/I, C, C++, Pascal, Modula-2, Ada, Java, C#.

2.General-purpose languages for smaller programs: BASIC, Visual Basic, Pascal, Python.

3.Mathematical calculation, science, and engineering: FORTRAN, APL, Maple, and the general-purpose languages named above.

4.Business data processing: COBOL, RPG. Where microcomputers are involved, BASIC, C, and languages associated with specific database products are also widely used.

5.Artificial intelligence and programs of extreme logical complexity: Lisp and Prolog.

6.String handling and scripting: SNOBOL, REXX, Awk, Perl, Python, VBSCRIPT, JavaScript.

Another useful classification is based on the way the program is organized.

1.Sequential languages treat the program as a series of steps, with an occasional GOTO statement as a way of breaking out of the sequence. In this category are FORTRAN, BASIC, and COBOL

(though COBOL also allows programs to be written in a style more like a block-structured language).

2.Block-structured languages encourage structured programming by allowing the programmer to group statements into functional units. (See STRUCTURED PROGRAMMING.) This category originated with Algol and now includes Pascal, Modula-2, C, PL/I, and Ada.

3.Object-oriented languages allow the programmer to define new data types and associate procedures with them. Languages of this type include C++, Java, C#, object-oriented extensions of Pascal, and Smalltalk.

4.Symbolic languages allow the program to examine and modify itself, treating instructions as data. Lisp and Prolog fall into this category.

Usage note: Although names of some programming languages are normally written in all capital letters, names of most languages are not, even if they are acronyms. Usage varies from language to language. With some, usage has shifted over the years. See also BASIC (Usage note).

See also ARRAY; BACKTRACKING; COMMENT; EXTREME PROGRAMMING;

LOGO; LOOP; OBJECT ORIENTED PROGRAMMING; RECURSION; SOFTWARE ENGINEERING; SORT; STRUCTURED PROGRAMMING; TOP-DOWN PROGRAMMING.

project the set of all files needed to produce the ready-to-use version of a program. Typically, the compiler accepts procedures from several different files and combines them into one executable (EXE) file. See MAKE; LINK.

FIGURE 205. Project management: Gantt chart for moving to a new home

project management the scheduling of a complex project involving many different tasks. A typical task requires some resources and a certain amount of time; it also requires that certain other tasks have already been finished. You may sometimes schedule two tasks to be performed simul-

taneously if they don’t overtax the supply of available resources, but when the tasks are sequential, you must schedule them in the proper order. For example, the engines on the wings of an airplane cannot be installed until the wings have been built. A project manager program takes the information the user enters for each task and then determines how to schedule the tasks. The results are often presented in the form of a diagram called a Gantt chart (see Figure 205).

Prolog a programming language developed in the early 1970s by Alain Colmerauer at the University of Marseilles and standardized by the ISO in 1995. Prolog is used for writing computer programs that model human thinking. It exemplifies logic programming, a kind of programming developed by Robert Kowalski of the University of London.

In ordinary programming, a program describes the steps that a computer is to work through in order to solve a problem. In logic programming, the program gives the computer facts about the problem, plus rules by means of which other facts can be inferred. The computer then applies a fixed procedure to solve the problem automatically.

For example, Prolog can chain together the fact “Atlanta is in Georgia” and the rule “X is in the U.S.A. if X is in Georgia” to answer the question, “Is Atlanta in the U.S.A.?” In Prolog, the fact and the rule are:

located_in(atlanta,georgia). located_in(X,usa) :-located_in(X,georgia).

The question (called a query) is typed:

?-located_in(atlanta,usa).

and is answered “yes.”

One of the most important properties of Prolog is its ability to backtrack, that is, to back up and try alternative solutions. This is necessary whenever the search starts pursuing a chain of rules that do not lead to a solution.

Prolog is not confined to the simple kind of logic described here. It can implement all types of algorithms, including sorting, numerical computation, and parsing. See also ANONYMOUS VARIABLE; ARTIFICIAL INTELLIGENCE; BACKTRACKING; SINGLETON VARIABLE.

PROM (Programmable Read-Only Memory) a type of computer memory that can be programmed once but not reprogrammed. See also EPROM.

promiscuous mode a mode in which a computer reads all the data packets on the network, not just those addressed to it. See SNIFFER.

prompt a symbol that appears on a computer terminal screen to tell the user that the computer is ready to receive input. See also COMMAND PROMPT.

pron deliberate misspelling of porn, often used to discuss pornography when a chat filter blocks other words for it.

prop an object placed within the scene of an animation.

properties the attributes of any object. Under Windows, menus titled “Properties” are the usual way of changing settings. In Windows, rightclick on an object to change its properties. For example, the properties of an icon specify what it looks like and what should happen when the user clicks on it.

proportional pitch the use of characters with different widths in a single typeface. For example, in proportional-pitch type, M is wider than I. Compared to a fixed-pitch typewriter or printer, this improves the appearance of the type and makes it more readable. Most books and newspapers are set in proportional type. See TYPE; TYPEFACE. For an illustration, see PITCH.

Because the letters are of different widths, it is not possible to count letter spaces in proportional-pitch type the way one does on a typewriter.

See TYPESETTING MISTAKES.

proprietary owned by a specific company or individual. A feature of a computer is proprietary if one company has exclusive rights to it.

protocol a standard way of carrying out data transmission between computers. See HANDSHAKING; ATM (definition 4); DHCP; FTP; GOPHER; HTTP;

IIOP; IMAP; IPV6; IPXSPX; KERBEROS; KERMIT; NETBEUI; POP; PPP; REALAUDIO; SAMBA; SMTP; SOAP; TCP/IP; TELNET; TWAIN; VOIP; X.25.

proxy an item that represents something else. See also PROXY SERVER.

proxy server a computer that saves information acquired from elsewhere on the INTERNET and makes it available to other computers in its immediate area. For example, if several users connect to the same WEB SITE through a proxy server, each page of information will be downloaded from that site only once and then provided to all the users.

A disadvantage of proxy servers is that they make it impossible to count HITs accurately.

PS 2

1.an advanced version (Level 2) of the POSTSCRIPT graphics language.

2.Sony Playstation 2, a video game machine.

PS/2 see IBM PC.

PS/2 keyboard, PS/2 mouse a keyboard or mouse with a small round connector of the type originally used on the IBM PS/2 but now widely used on other PC-compatible computers.

pseudocode an outline of a computer program, written in a mixture of a programming language and English. Writing pseudocode is one of the best ways to plan a computer program. For example, here is a pseudocode outline of a Pascal program to find the largest of a set of 10 numbers:

Here is the program that results from translating all of the pseudocode into genuine Pascal:

PROGRAM findthelargest (INPUT, OUTPUT); VAR num, largest, count : INTEGER; BEGIN

count := O; largest := O; REPEAT

count := count + 1; read(num);

IF num > largest THEN largest := num; UNTIL count = 10;

writeln(’The largest number was ’,largest)

END.

(This program assumes that the largest number will be greater than zero.)

The advantage of pseudocode is that it allows the programmer to concentrate on how the program works while ignoring the details of the language. By reducing the number of things the programmer must think about at once, this technique effectively amplifies the programmer’s intelligence.

PST the file extension on archived e-mail messages in Microsoft Outlook.

public domain the status of literature, art, music, or software that was not copyrighted, or whose copyright has expired and not been renewed.

A computer program is in the public domain if it is not covered by any kind of copyright. Few substantial public-domain programs exist, but the term “public domain” is often used incorrectly to describe other kinds of freely copyable software (see FREE SOFTWARE). See also COPYRIGHT.

public key a publicly revealed password used for encoding private messages to a particular recipient. The recipient then uses his or her own secret PRIVATE KEY to decrypt the message. See ENCRYPTION.

public html typical name for the directory in which an individual user’s WEB PAGE is stored under UNIX.

pull the process whereby the user retrieves information from a network at the user’s request, as in traditional web browsing; contrast PUSH (definition 2).