Internet Dictionary
Click on a letter to see the relevant terms: A B C D E F G H I J K L M N O P Q R S T U V W Z

Packet Communications on the Internet are broken down into units of data called packets. Each packet contains the source address, destination address and data in TCP/IP format. Short messages may need only a few packets, whereas large file transfers may require many packets.

Parallel When transmitting digital data from one place to another, you can do it in either of two ways: parallel or serial. The basic unit of digital data is the byte, which is 8 bits of data. Older computers use internal transmission paths with 8 parallel conductors. This way, they could move one byte of data (all 8 bits simultaneously) from one internal point to another. Newer computers use parallel paths of 32 bits. This is one reason why they are much faster.

PC Personal Computer.

PDF Portable Document Format. This is the format used by Adobe Acrobat. It's called portable because it works on different operating systems like Windows, Unix, MacIntosh, etc. PDF files look exactly like the originals, complete with fonts and graphics. You can recognize a PDF file by its extension of ".pdf". PDF files are created with Adobe Acrobat and can be read with the Acrobat Reader. For instance, juggler.pdf indicates an Acrobat file.

Peripheral Any external hardware that you connect to your computer through one of its connectors. Examples of peripherals are printers, keyboards, and monitors.

Ping This a short program used to check if communication exists between two computer nodes. For instance, assume computer A has an IP address of 123.456.789.123 and computer B has an IP address of 987.654.321.987. If somebody at computer A enters the command "ping 987.654.321.987", a packet of data is sent to computer B. If a connection exists, computer B will automatically send back a reply to computer A. On the Internet, it takes a few hundred milliseconds for the reply to come back.

Pixel The smallest dot on a computer screen. For instance, on a standard VGA screen, there are 640 pixels across the screen and 480 down. This means a horizontal line on the screen consists of 640 small dots clustered together to give the appearance of a solid line. With a VGA screen, you can draw 480 horizontal lines, each with 640 pixels in it. Therefore, a standard VGA screen has a total of 640 X 480, or 307,200 pixels.

PKUNZIP The opposite of PKZIP. Whereas PKZIP compresses a file, PKUNZIP decompresses (or uncompresses) the file back to its original contents.

PKZIP A program that compresses files by looking for and recoding redundant information. The compression ratio depends on the type of file. Typical compression ratios are around 2 to 1. For instance, an executable file named sunrise.exe with a length of 100 Kbytes might be compressed to 50 Kbytes with the command PKZIP sunrise.exe. To retrieve the original file, another program called PKUNZIP is used. A command like PKUNZIP sunrise.zip would restore the original file sunrise.exe.

POP Post Office Protocol. This is a user-to-server protocol, a set of communication rules for your computer and mail server. POP lets you download your e-mail from a POP server.

Port A typical PC has input/output (I/O) devices like a keyboard, a monitor, a printer, and a modem. The connectors that these devices plug into are called ports. Each port has a unique bus address that the central processing unit (CPU) uses when sending and receiving data from these ports. For instance, here are the typical port addresses for a PC: Com1 - 03F8, Com2 - 02F8, LPT1 - 0378, LPT2 - 0278, etc. When the CPU sends an address to the bus, only the addressed device is turned on. Port addresses are like TV channel frequencies; they allow the CPU to tune in (send or receive data) to only one port at a time. Ports have a different meaning on the Internet; they refer to the type of protocol being used: FTP - port 21, Telnet - port 23, Gopher - port 70, HTTP - port 80, NNTP - port 119, and WAIS - port 210. A port number is sometimes included in the URL address. For instance, http://www.malvino.com:80. Notice that the port number 80 comes after the domain name. Port numbers less than 1024 are used for Internet services such as FTP, e-mail, news, etc. In conclusion, an Internet port number is like a TV channel number. It allows the Internet to tune into the associated protocol: port 21 brings in FTP, port 23 brings in Telnet, etc.

PPP Point-to-Point Protocol. Another serial-transmission protocol similar to SLIP because it connects your computer to the Internet over phone lines. It includes more error-checking and password protection. PPP is gradually replacing SLIP. Both SLIP and PPP make your PC an Internet peer, meaning it is assigned an IP address.

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