Click on the links below to find information on any part of Internet lingo.
A public-domain Web server developed by a loosely-knit group of programmers. The first version of Apache, based on the NCSA httpd Web server, was developed in 1995. Because it was developed from existing NCSA code plus various patches, it was called a patchy server – hence the name Apache Server.
As a result of its sophisticated features, excellent performance, and low price (it’s free), Apache has became the world’s most popular Web server. By some estimates, it is used to host more than 50% of all Web sites in the world. Core development of the Apache Web server is performed by a group of about 20 volunteer programmers, called the Apache Group. However, because the source code is freely available, anyone can adapt the server for specific needs, and there is a large public library of Apache add-ons. In many respects, development of Apache is similar to development of the Linux operating system. The original version of Apache was written for UNIX, but there are now versions that run under other platforms.
Used in FTP and the WWW, this is a type of file, usually any kind of file that you can read (like a text file) falls under this classification (HTML files should be ASCII files).
A specification for a dynamically created Web page with a .ASP extension that contain either Visual Basic or Jscript code. When a browser requests an ASP page, the Web server generates a page with HTML code and sends it back to the browser. So ASP pages are similar to CGI scripts, but they enable Visual Basic programmers to work with familiar tools.
The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second(bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz).
The bandwidth is particularly important for I/O devices. For example, a fast disk drive can be hampered by a bus with a low bandwidth. This is the main reason that new buses, such as AGP, have been developed for the PC.
Used in FTP and the WWW, this is a type of file, usually any kind of file that is unreadable as text falls under this classification (graphic images, sound files, etc. should be BINARY files)
Blue Screen of Death
An error that can appear on computers running Microsoft Windows XP or Vista. Jokingly called the blue screen of death because when the error occurs, the screen turns blue, and the computer almost always freezes and requires rebooting.
Short for Web browser, a software application used to locate and display Web pages. The two most popular browsers are Microsoft Internet Explorer, FireFox, and Safari.
An object oriented language that can be compiled and run on a server via the source file of sample.c and then compiled into an executable file.
Pronounced cash, a special high-speed storage mechanism. It can be either a reserved section of main memory or an independent high-speed storage device. Two types of caching are commonly used in personal computers: memory caching and disk caching.
A memory cache, sometimes called a cache store or RAM cache, is a portion of memory made of high-speed static RAM (SRAM) instead of the slower and cheaper dynamic RAM (DRAM) used for main memory. Memory caching is effective because most programs access the same data or instructions over and over. By keeping as much of this information as possible in SRAM, the computer avoids accessing the slower DRAM.
Some memory caches are built into the architecture of microprocessors. The Intel 80486 microprocessor, for example, contains an 8K memory cache, and the Pentium has a 16K cache. Such internal caches are often called Level 1 (L1) caches. Most modern PCs also come with external cache memory, called Level 2 (L2) caches. These caches sit between the CPU and the DRAM. Like L1 caches, L2 caches are composed of SRAM but they are much larger.
Disk caching works under the same principle as memory caching, but instead of using high-speed SRAM, a disk cache uses conventional main memory.
The most recently accessed data from the disk (as well as adjacent sectors) is stored in a memory buffer. When a program needs to access data from the disk, it first checks the disk cache to see if the data is there. Disk caching can dramatically improve the performance of applications, because accessing a byte of data in RAM can be thousands of times faster than accessing a byte on a hard disk.
When data is found in the cache, it is called a cache hit, and the effectiveness of a cache is judged by its hit rate. Many cache systems use a technique known as smart caching, in which the system can recognize certain types of frequently used data. The strategies for determining which information should be kept in the cache constitute some of the more interesting problems in computer science.
Abbreviation of Common Gateway Interface, a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any programming language, including C, Perl, Java, or Visual Basic. CGI programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form’s data once it’s submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user’s machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX controls. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server.
One problem with CGI is that each time a CGI script is executed, a new process is started. For busy Web sites, this can slow down the server noticeably. A more efficient solution, but one that it is also more difficult to implement, is to use the server’s API, such as ISAPI or NSAPI. Another increasingly popular solution is to use Java servlets.
A Unix command for scheduling jobs to be executed sometime in the future. A cron is normally used to schedule a job that is executed periodically – for example, to send out a notice every morning. It is also a daemon process, meaning that it runs continuously, waiting for specific events to occur.
(1) Short for Domain Name System (or Service), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they’re easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 126.96.36.199. The DNS system is, in fact, its own network. If one DNS server doesn’t know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.
(1) refers to Web content that changes each time it is viewed. For example, the same URL could result in a different page depending on any number of parameters, such as:
- Geographic location of the reader
- Time of day
- Previous pages viewed by the reader
- Profile of the reader
(2) When capitalized, Dynamic HTML refers to new HTML extensions that will enable a Web page to react to user input without sending requests to the Web server. Microsoft and Netscape have submitted competing Dynamic HTML proposals to W3C, which is producing the final specification.
Aliasing allows you to have multiple e-mail addresses sent to a specific POP e-mail account (ie. pick up firstname.lastname@example.org, email@example.com, etc. from one POP account rather than from several separate ones).
Forwarding allows you to have e-mail forwarded from a specific address or POP account to another POP account (ie. have all e-mail sent to firstname.lastname@example.org sent to your POP account provided by your ISP).
A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
There are several types of firewall techniques:
Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers.
This is very effective, but can impose a performance degradation.
Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking. Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses. In practice, many firewalls use two or more of these techniques in concert. A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.
Abbreviation of File Transfer Protocol, the protocol used on the Internet for sending files.
Short for HyperText Markup Language, the authoring language used to create documents on the World Wide Web. HTML is similar to SGML, although it is not a strict subset.
The regulatory agency that handles the assignment and database tracking of active/inactive/available domain names. Each country has their own NIC registry service for handling foreign (or domestic) domain names.
(Internet Presence Provider) provides presences on the Internet, usually provides web hosting and e-mail services (this is what we do).
(Internet Service Provider) provides connectivity to the Internet, usually via modem and dialup lines (we DO NOT provide ISP services)
Java: A high-level programming language developed by Sun Microsystems. Java was originally called OAK, and was designed for handheld devices and set-top boxes. Oak was unsuccessful so in 1995 Sun changed the name to Java and modified the language to take advantage of the burgeoning World Wide Web. Java is an object-oriented language similar to C++, but simplified to eliminate language features that cause common programming errors. Java source code files (files with a .java extension) are compiled into a format called bytecode (files with a .class extension), which can then be executed by a Java interpreter. Compiled Java code can run on most computers because Java interpreters and runtime environments, known as Java Virtual Machines (VMs), exist for most operating systems, including UNIX, the Macintosh OS, and Windows. Bytecode can also be converted directly into machine language instructions by a just-in-time compiler (JIT). Java is a general purpose programming language with a number of features that make the language well suited for use on the World Wide Web. Small Java applications are called Java applets and can be downloaded from a Web server and run on your computer by a Java-compatible Web browser, such as Netscape Navigator or Microsoft Internet Explorer.
The kernel is the core of the operating system. It’s primary functions are controlling execution of processes, handling memory management, providing a file system, and providing a portable interface through which programs may communicate with hardware.
A freely-distributable implementation of UNIX that runs on a number of hardware platforms, including Intel and Motorola microprocessors. It was developed mainly by Linus Torvalds. Because it’s free, and because it runs on many platforms, including PCs, Macintoshes and Amigas, Linux has become extremely popular over the last couple years. Another popular, free version of UNIX that runs on Intel microprocessors is FreeBSD.
Short for Practical Extraction and Report Language, Perl is a programming language developed by Larry Wall, especially designed for processing text. Because of its strong text processing abilities, Perl has become one of the most popular languages for writing CGI scripts. Perl is an interpretive language, which makes it easy to build and test simple programs.
(Point of Presence)Physical e-mail accounts you log into with a username and password to pick up any e-mail sent/forwarded to that account
A period after a domain name is registered or transferred when the domain name is updated amoung all the nameservers found on the Internet around the world. This period usually lasts 3-7 days and may result in visitors not being able to visit the domain name until the period is over.
Router: A device that connects two LANs. Routers are similar to bridges, but provide additional functionality, such as the ability to filter messages and forward them to different places based on various criteria. The Internet uses routers extensively to forward packets from one host to another.
is based on a public key system which means that every user has 2 digital keys one to encrypt information, and the other to decrypt. Authentication of both sender and recipient is provided with this method.
SCSI (Small Computer Systems Interface) SCSI (pronounced “scuzzy”) differs in a big way from the ST-506 standard. SCSI is actually a smart bus – it is controlled with a microprocessor – and it allows the addition of up to seven devices (not necessarily just hard drives – scanners, printers and other devices often use SCSI) to the computer. SCSI drives are also usually large and fast. Using one will require the addition of a SCSI adapter. In the early days of SCSI, a lot of devices were made that didn’t talk to each other, but those days are behind us for the most part. SCSI II is a newer standard which allows data transfer rates that are a lot higher than the older SCSI standard. SCSI and SCSI II devices should be able to coexist on a SCSI II bus. There are also Fast SCSI and Wide SCSI, two standards that allow even greater bandwidth across the SCSI bus. These two standards are most often seen on high end workstations or file servers. The latest SCSI standard is SCSI III. At this point in time, a few SCSI III drives, cables and controllers are available. Each SCSI device on the SCSI bus requires a unique SCSI number, from 1 to 7 (the computer’s SCSI number is 0). SCSI devices are daisy chained together by cabling, and the device at the end of the daisy chain has to have a terminator resistor.
The outermost layer of a program. Shell is another term for user interface. Operating systems and applications sometimes provide an alternative shell to make interaction with the program easier. For example, if the application is usually command driven, the shell might be a menu-driven system that translates the user’s selections into the appropriate commands. (2) Sometimes called command shell, a shell is the command processor interface. The command processor is the program that executes operating system commands. The shell, therefore, is the part of the command processor that accepts commands. After verifying that the commands are valid, the shell sends them to another part of the command processor to be executed. UNIX systems offer a choice between several different shells, the most popular being the Cshell, the Bourne shell, and the Korn shell. Each offers a somewhat different command language.
is a piece of software that operates on an online storefront. The “shopping cart” keeps track of all the items that a buyer wants to purchase, allowing the shopper to pay for the whole order at once.
Short for Simple Mail Transfer Protocol, a protocol for sending e-mail messages between servers. Most e-mail systems that send mail over the Internet use SMTP to send messages from one server to another; the messages can then be retrieved with an e-mail client using either POP or IMAP. In addition, SMTP is generally used to send messages from a mail client to a mail server. This is why you need to specify both the POP or IMAP server and the SMTP server when you configure your e-mail application.
SONET stands for Synchronous Optical NETwork. The SONET format allows different types of formats to be transmitted on one line. SONET is a long term solution for a mid-span-meet between vendors. The other major advantage is that SONET allows ADDING and DROPING signals with a single multiplexer.
Short for server-side include, a type of HTML comment that directs the Web server to dynamically generate data for the Web page whenever it is requested. The basic format for SSIs are <!–#command tag=”value”> Where #command can be any of various commands supported by the Web server. The simplest command is #include, which inserts the contents of another file. This is especially useful for ensuring that boilerplate components, such as headers and footers, are the same on all pages throughout a Web site. To change a boilerplate element, you need only modify the include file, instead of updating every individual Web page. SSIs can also be used to execute programs and insert the results. They therefore represent a powerful tool for Web developers. There is no official standard for SSIs, so every Web server is free to support different SSIs in different manners. However, many SSI commands, such as #include and #exec, have become de facto standards. Web pages that contain SSIs often end with a .shtml extension, though this is not a requirement. The filename extension enables the Web server to differentiate those pages that need to be processed before they are sent to the browser.
A terminal emulation program for TCP/IP networks such as the Internet. The Telnet program runs on your computer and connects your PC to a server on the network. You can then enter commands through the Telnet program and they will be executed as if you were entering them directly on the server console. This enables you to control the server and communicate with other servers on the network. To start a Telnet session, you must log in to a server by entering a valid username and password. Telnet is a common way to remotely control Web servers.
Pronounced yoo-niks, a popular multi-user, multitasking operating system developed at Bell Labs in the early 1970s. Created by just a handful of programmers, UNIX was designed to be a small, flexible system used exclusively by programmers. Although it has matured considerably over the years, UNIX still betrays its origins by its cryptic command names and its general lack of user-friendliness. This is changing, however, with graphical user interfaces such as MOTIF. UNIX was one of the first operating systems to be written in a high-level programming language, namely C. This meant that it could installed on virtually any computer for which a C compiler existed. Due to its portability, flexibility, and power, UNIX has become the leading operating system for workstations. Historically, it has been less popular in the personal computer market, but the emergence of a new version called Linux is revitalizing UNIX across all platforms
Abbreviation of Uniform Resource Locator, the global address of documents and other resources on the World Wide Web. The first part of the address indicates what protocol to use, and the second part specifies the IP address or the domain name where the resource is located. For example, the two URLs below point to two different files at the domain pcwebopedia.com. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol:
(World Wide Web) refers to the vast web sites and such that span the Internet.