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Glossary P
 A packet is the unit of data that is routed between an origin and a destination on the Internet or any other packet-switched network. When any file (e-mail message, HTML file, Graphics Interchange Format file, Uniform Resource Locator request, and so forth) is sent from one place to another on the Internet, the Transmission Control Protocol (TCP) layer of TCP/IP divides the file into "chunks" of an efficient size for routing. Each of these packets is separately numbered and includes the Internet address of the destination. The individual packets for a given file may travel different routes through the Internet. When they have all arrived, they are reassembled into the original file (by the TCP layer at the receiving end).
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 1) On the World Wide Web, a page is a file notated with the Hypertext Markup Language (HTML). Usually, it contains text and specifications about where image or other multimedia files are to be placed when the page is displayed. You can think of a Web site as a book (albeit a hypertext kind of book rather than a sequentially arranged kind of book) that arrives a page at a time as you request each one. Each page is an individual HTML file with its own Web address (URL). The first page you usually request at a site is known as the home page. (Most home pages have a default name that doesn't have to be specified; you only need to enter the domain name for the site itself.) With frames, multiple pages (HTML files) can be downloaded to a browser and presented on designated sections of the display screen at the same time.
2) In a computer's random access memory (RAM), a page is a group of memory cells that are accessed as part of a single operation. That is, all the bits in the group of cells are changed at the same time. In some kinds of RAM, a page is all the memory cells in the same row of cells. In other kinds of RAM, a page may represent some other group of cells than all those in a row.
3) In computer systems that use virtual memory (also known as virtual storage), a page is a unit of data storage that is brought into real storage (on a personal computer, RAM) from auxiliary storage (on a personal computer, usually the hard disk) when a requested item of data is not already in real storage (RAM).
4) In printing, a page is what is printed on a single piece of paper.
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 A password is a form of secret authentication data that is used to control access to a resource. The password is kept secret from those not allowed access, and those wishing to gain access are tested on whether or not they know the password and are granted or denied access accordingly.
The use of passwords goes back to ancient times. Sentries guarding a location would challenge for a password. They would only allow a person in if they knew the password. In modern times, passwords are used to control access to protected computer operating systems, mobile phones, cable TV decoders, automated teller machines (ATMs), etc. A typical computer user may require passwords for many purposes: logging in to computer accounts, retrieving e-mail from servers, accessing files, databases, networks, web sites, and even reading the morning newspaper online.
Despite the name, there is no need for passwords to be actual words; indeed passwords which are not actual words are harder to guess (a desirable property). Note that password is often used to describe what would be more accurately called a pass phrase. Passcode is sometimes taken to imply that the information used is purely numeric, such as the personal identification number (PIN) commonly used for ATM access. Passwords are generally short enough to be memorized.
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 A patent is a set of exclusive rights granted by a state to a patentee (the inventor or assignee) for a fixed period of time in exchange for the regulated, public disclosure of certain details of a device, method, process or composition of matter (substance) (known as an invention) which is new, inventive, and useful or industrially applicable. Modern patents for inventions include a set of claims which provide the basis for determining the exclusive rights, i.e the scope of protection. The way the exclusive rights are determined is subject to applicable laws.
The exclusive right granted to a patentee in most countries is the right to prevent or exclude others from making, using, selling, offering to sell or importing the claimed invention. The rights given to the patentee do not include the right to make, use, or sell the invention themselves. The patentee may have to comply with other laws and regulations to make use of the claimed invention. So, for example, a pharmaceutical company may obtain a patent on a new drug but will be unable to market the drug without regulatory approval, or an inventor may patent an improvement to a particular type of laser, but be unable to make or sell the new design without a license from the owner of an earlier broader patent covering lasers of that type.
The term "patent" originates from the Latin word patere which means "to lay open" (i.e., make available for public inspection) and the term letters patent, which originally denoted royal decrees granting exclusive rights to certain individuals or businesses.
When people refer to a "patent", they are most usually referring to a right granted to anyone who invents or discovers any new and useful process, machine, article of manufacture, or composition of matter, or any new and useful improvement thereof. Patents may be referred to as "utility patents" in countries such as the United States to distinguish them from other types of patents but should not be confused with utility models granted by other countries. Examples of particular species of patents for inventions include biological patents, business method patents, chemical patents and software patents.
Some other types of intellectual property right are referred to as "patents" in some jurisdictions: industrial design rights are called "design patents" in some jurisdictions (they protect the visual design of objects that are not purely utilitarian), plant breeders' rights are sometimes called "plant patents", and utility models or Gebrauchsmuster are sometimes called "petty patents". This article relates primarily to the patent for an invention, although so-called petty patents and utility models may also be granted for inventions.
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Also see DOS.
 PC-DOS (Personal Computer - Disk Operating System) was the first widely-installed operating system used in personal computers. It was developed for IBM by Bill Gates and his fledgling Microsoft Corporation for installation in IBM's first lines of PCs. Gates marketed an almost identical version of the operating system called MS-DOS (Microsoft - Disk Operating System). Most users of either DOS system have usually referred to their system as just DOS. Like MS-DOS, PC-DOS was (and still is) a non-graphical line-oriented command-driven operating system, with a relatively simple interface but not overly "friendly" user interface. Its prompt to enter a command looks like this:
C:>
The first Microsoft Windows operating system was really an application that ran on top of the MS-DOS operating system. Today, Windows operating systems continue to support DOS (or a DOS-like user interface) for special purposes by emulating the operating system.
In the 1970s before the personal computer was invented, IBM had a different and unrelated DOS (Disk Operating System) that ran on smaller business computers. It was replaced by IBM's VSE operating system.
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 Peer-to-peer is a communications model in which each party has the same capabilities and either party can initiate a communication session. Other models with which it might be contrasted include the client/server model and the master/slave model. In some cases, peer-to-peer communications is implemented by giving each communication node both server and client capabilities. In recent usage, peer-to-peer has come to describe applications in which users can use the Internet to exchange files with each other directly or through a mediating server.
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 The Pentium is a widely-used personal computer microprocessor from the Intel Corporation. First offered in 1993, the Pentium quickly replaced Intel's 486 microprocessor as the microchip-of-choice in manufacturing a personal computer. The original Pentium model includes two processors on one chip that contains 3.1 million transistors.
The Pentium Pro, released in 1995, was designed for PC servers and workstation that needed to serve multiple users or needed the speed required for graphics-intensive applications. In addition to the microprocessor, the Pentium Pro includes another microchip containing cache memory that, being closer to the processor than the computer's main memory (RAM), speeds up computer operation. The Pentium Pro contains 5.5 million transistors.
The Pentium II is a Pentium Pro with Intel's MMX technology included. It comes in microprocessor clock speeds of 233 MHz (millions of cycles per second), 266 MHz, and 300 MHz. It's suitable for applications that include motion video and 3-D images. Among the Pentium II's features are a 512 KB (kilobyte) level-two (L1 and L2) memory cache and a 32 KB L1 and L2 cache, twice that of the Pentium Pro processor. The L2 cache can include error correcting code (ECC).
The latest Pentium II's are Celeron, a low-end Pentium without the L2 cache, and Xeon, a high-end Pentium that replaces the Pentium Pro for enterprise server and workstation computers.
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 Perl is a script programming language that is similar in syntax to the C language and that includes a number of popular Unix facilities such as SED, awk, and tr. Perl is an interpreted language that can optionally be compiled just before execution into either C code or cross-platform bytecode. When compiled, a Perl program is almost (but not quite) as fast as a fully precompiled C language program. Perl is regarded as a good choice for developing common gateway interface (CGI) programs because it has good text manipulation facilities (although it also handles binary files). It was invented by Larry Wall.
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 Phishing is an e-mail fraud method in which the perpetrator sends out legitimate-looking email in an attempt to gather personal and financial information from recipients. Typically, the messages appear to come from well known and trustworthy Web sites. Web sites that are frequently spoofed by phishers include PayPal, eBay, MSN, Yahoo, BestBuy, and America Online. A phishing expedition, like the fishing expedition it's named for, is a speculative venture: the phisher puts the lure hoping to fool at least a few of the prey that encounter the bait.
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 A PIN is a personal identification number. PINs are commonly assigned to bank customers for use with automatic cash dispensers. They are also used, sometimes with a security token, for individual access to computer networks or other secure systems.
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 Portability is a characteristic attributed to a computer program if it can be used in an Operating systems other than the one in which it was created without requiring major rework. Porting is the task of doing any work necessary to make the computer program run in the new environment. In general, programs that adhere to standard program interfaces such as the X/Open Unix 95 standard C language interface are portable. Ideally, such a program needs only to be compiled for the operating system to which it is being ported. However, programmers using standard interfaces also sometimes use operating system extensions or special capabilities that may not be present in the new operating system. Uses of such extensions have to be removed or replaced with comparable functions in the new operating system. In addition to language differences, porting may also require data conversion and adaptation to new system procedures for running an application.
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 POSIX (Portable Operating System Interface) is a set of standard Operating system interfaces based on the Unix operating system. The need for standardization arose because enterprises using computers wanted to be able to develop programs that could be moved among different manufacturer's computer systems without having to be recoded. Unix was selected as the basis for a standard system interface partly because it was "manufacturer-neutral." However, several major versions of Unix existed so there was a need to develop a common denominator system.
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 PowerPC is a microprocessor architecture that was developed jointly by Apple, IBM, and Motorola. The PowerPC employs reduced instruction-set computing (RISC). The three developing companies have made the PowerPC architecture an open standard, inviting other companies to build on it.
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 PPP (Point-to-Point Protocol) is a protocol for communication between two computers using a serial interface, typically a personal computer connected by phone line to a server. For example, your Internet server provider may provide you with a PPP connection so that the provider's server can respond to your requests, pass them on to the Internet, and forward your requested Internet responses back to you. PPP uses the Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) service. Essentially, it packages your computer's TCP/IP packets and forwards them to the server where they can actually be put on the Internet.
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 In information technology, a protocol (from the Greek protocollon, which was a leaf of paper glued to a manuscript volume, describing its contents) is the special set of rules that end points in a telecommunication connection use when they communicate. Protocols exist at several levels in a telecommunication connection. For example, there are protocols for the data interchange at the hardware device level and protocols for data interchange at the application program level. In the standard model known as Open Systems Interconnection (OSI), there are one or more protocols at each layer in the telecommunication exchange that both ends of the exchange must recognize and observe. Protocols are often described in an industry or international standard.
On the Internet, there are the TCP/IP protocols, consisting of:
There are many other Internet protocols, such as the Border Gateway Protocol (BGP) and the Dynamic Host Configuration Protocol (DHCP).
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 In an enterprise that uses the Internet, a proxy server is a server that acts as an intermediary between a workstation user and the Internet so that the enterprise can ensure security, administrative control, and caching service. A proxy server is associated with or part of a gateway server that separates the enterprise network from the outside network and a firewall server that protects the enterprise network from outside intrusion.
A proxy server receives a request for an Internet service (such as a Web page request) from a user. If it passes filtering requirements, the proxy server, assuming it is also a cache server, looks in its local cache of previously downloaded Web pages. If it finds the page, it returns it to the user without needing to forward the request to the Internet. If the page is not in the cache, the proxy server, acting as a client on behalf of the user, uses one of its own IP addresses to request the page from the server out on the Internet. When the page is returned, the proxy server relates it to the original request and forwards it on to the user.
To the user, the proxy server is invisible; all Internet requests and returned responses appear to be directly with the addressed Internet server. (The proxy is not quite invisible; its IP address has to be specified as a configuration option to the browser or other protocol program.)
An advantage of a proxy server is that its cache can serve all users. If one or more Internet sites are frequently requested, these are likely to be in the proxy's cache, which will improve user response time. In fact, there are special servers called cache servers. A proxy can also do logging.
The functions of proxy, firewall, and caching can be in separate server programs or combined in a single package. Different server programs can be in different computers. For example, a proxy server may in the same machine with a firewall server or it may be on a separate server and forward requests through the firewall.
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 In cryptography, a public key is a value provided by some designated authority as an encryption key that, combined with a private key derived from the public key, can be used to effectively encrypt messages and digital-signatures.
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 A PKI (public key infrastructure) enables users of a basically unsecure public network such as the Internet to securely and privately exchange data and money through the use of a public and a private cryptographic key pair that is obtained and shared through a trusted authority. The public key infrastructure provides for a digital certificate that can identify an individual or an organization and directory services that can store and, when necessary, revoke the certificates. Although the components of a PKI are generally understood, a number of different vendor approaches and services are emerging. Meanwhile, an Internet standard for PKI is being worked on.
The public key infrastructure assumes the use of public key cryptography, which is the most common method on the Internet for authenticating a message sender or encrypting a message. Traditional cryptography has usually involved the creation and sharing of a secret key for the encryption and decryption of messages. This secret or private key system has the significant flaw that if the key is discovered or intercepted by someone else, messages can easily be decrypted. For this reason, public key cryptography and the public key infrastructure is the preferred approach on the Internet. (The private key system is sometimes known as symmetric cryptography and the public key system as asymmetric cryptography.)
A public key infrastructure consists of:
- A certificate authority (CA) that issues and verifies digital certificate. A certificate includes the public key or information about the public key
- A registration authority (RA) that acts as the verifier for the certificate authority before a digital certificate is issued to a requestor
- One or more directories where the certificates (with their public keys) are held
- A certificate management system
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