Ymodem

Ymodem is an error-correcting protocol for a modem that uses larger data blocks for greater efficiency. Modems that agree on using the Ymodem protocol send data in 1024-byte blocks. Blocks received successfully are not acknowledged. Blocks with errors are acknowledged (with a NAK or negative acknowledgement) and the blocks are retransmitted. Ymodem is similar to Xmodem-1K except that a batch mode is provided. In batch mode, a number of files can be sent with a single command. Ymodem uses cyclic redundancy checking as the method of error detection.

z coordinate

A z coordinate is the third-dimensional coordinate in a volume pixel, or voxel. Together with x and y coordinates, the z coordinate defines a location in a three-dimensional space.

z/OS

z/OS is the computer operating system for IBM’s zSeries 900 (z900) line of large (mainframe) servers. z/OS is a renamed and upgraded version of OS/390, which in turn evolved from the MVS operating system. IBM’s renamed servers and operating systems reflect a strategy to realign its products more closely with the Internet and its own ebusiness initiatives.

z/OS is described as an extremely scalable and secure high-performance operating system based on the 64-bit z/ Architecture. Like its predecessor, OS/390, z/OS lays claim to being highly reliable for running mission-critical applications. The operating system supports Web- and Java-based applications.

Z3950

Z39.50 is a standard communications protocol for the search and retrieval of bibliographic data in online databases. Z39.50 is used on the Internet to search the Online Public Access Catalogues (OPAC) of library holdings. It is also sometimes used to link disparate OPACs into a single "union" OPAC. Z39.50 is an American National Standards Institute (ANSI/NISO) standard.

zap

In general usage, zap (noun) is spiciness, kick, or a powerful force. Dishes with chili pepper have zap. This term may be traceable to a comic book convention in which the hurling of an electronic beam or bolt of electricity by a hero (or anti-hero) using a ray gun is often accompanied by a sound balloon that says "ZAP!!!" The term is also used in Paintball and in some computer games.

In information technology, zap has several meanings:

1) In programming, a zap (noun) is a precise and immediate correction for a computer code problem. Most proprietary software programs are distributed to customers as compiler code in the form of an unreadable string of computer binary digits. When a bug is detected after the software is released,the only way to fix the already compiled code is to overlay the bad code with a sequence of good code. This overlaying is known as zapping and the fix itself is a zap. IBM provides its mainframe software customers with a special program for applying zaps that is called SuperZap.

2) In computers, to zap (verb) can also mean to erase or get rid of something. On a Macintosh computer, to "zap the PRAM" is to erase PRAM so that the system can rebuild its contents. (See parameter RAM for this procedure.)

3) Relative to computer hardware, to zap (verb) can mean to ruin something electrically. Thus, a power surge when you don’t have a surge protector can zap a computer’s electronic components.

z-buffering

Z-buffering is an algorithm used in 3-D graphics to ensure that perspective works the same way in the virtual world as it does in the real one: a solid object in the foreground will block the view of one behind it. You’ve seen this illustrated in the real world when someone stands between you and the television screen. Z-buffering is a type of algorithm known as a Visual Surface Determination (VSD) algorithm. Z-buffering works by testing pixel depth and comparing the current position (z coordinate) with stored data in a buffer (called a z-buffer) that holds information about each pixel’s last postion. The pixel in the closer position to the viewer is the one that will be displayed, just as the person in front of the television is what the viewer sees rather than the screen. Z-buffering is one of three VSD algorithms commonly used for this purpose. The other two, BSP trees and depth sorting, work with polygons and consequently are less effective for portrayal of movement and overlap. Since it works at the pixel level, z-buffering can be demanding in terms of memory and processing time. Nevertheless, its more complex and life-like simulation of real-world object dynamics ensures its continuing popularity as a 3-D graphics development tool.

Zero Administration

Zero Administration for Windows is Microsoft’s initiative to help make its operating system easier to install and manage. The goal is to reduce the ownership costs of PCs, particularly in large corporations with many thousands of desktop computers to support.

Microsoft introduced Zero Administration in November 1996, at a time when Oracle and Sun were touting their own approach of "network computers” as a new way of doing corporate applications with less overhead than traditional PCs. Microsoft responded with its concept of Zero Administration. The idea was to include in all of Microsoft’s

Windows operating systems features that would simplify the time it took to install and maintain the system on thousands of machines—and at the same time reduce the costs of keeping PCs in corporate America. Microsoft provides Zero Administration packs for Windows NT and Windows 98. These packs include features to automatically send out operating-system and application software updates throughout the company from one workstation, and having these updates roll back to the previous version if something goes wrong during the process.

For Windows 2000, Zero Administration’s Group Policy feature lets administrators set rights and permissions for network and application access on the group level instead of having to do it for each individual user. If everyone in the legal department needs the same permissions and rights to applications, administrators need set this up only once for all the employees in the department.

ZIF

A ZIF (Zero Insertion Force) socket is the physical way that Intel’s 486 and Pentium microprocessors up to Pentium II connect on the computer motherboard to the data bus. As its name implies, the ZIF socket is designed for ease of manufacture and so that the average computer owner will be able to upgrade the microprocessor. The ZIF socket contains a lever that opens and closes, securing the microprocessor in place.

The ZIF interface evolved through eight variations, each with a differing number of pins and pin layout arrangements. Currently, the best-known is Socket 7, the configuration used in the Pentium microprocessor. (However, the Pentium Pro uses Socket 8.) With the Pentium II microprocessor, which is based on Intel’s new P6 micro architecture, Intel has changed to a new connection configuration called Slot 1. In this configuration, the microprocessor comes packaged in a cartridge that fits into a 242-contact or 330-contact slot in the motherboard.

The following table summarizes the Zero Insertion Force (ZIF) socket characteristics for different Intel processors.

Socket	Pins	Layout	Processor(s)	Voltage
0	168	Inline	486DX5 V
1	169	Inline	486DX,SX	5V
2	238	Inline	486DX,	5V
			SX,DX2
3	237	Inline	486DX,	3V
			SX,DX2,	or 5 V
			DX4
4	273	Inline	60 or	5V
			66 MHz
			Pentium
5	320	Staggered	Pentium	3V
6	235	Inline	486DX4	3V

Socket	Pins	Layout	Processor(s)	Voltage
7	321	Staggered	Pentium	3V
8	387	Staggered	Pentium	3V
			Pro

ZIP codes

ZIP (Zoning Improvement Plan) codes are postal codes in the United States that identify preassigned geographic boundaries and make mail sorting and delivery more efficient. Other countries have similar designations, usually referred to as post codes or postal codes.

Zip drive

Also see zipping.

A Zip drive is a small, portable disk drive used primarily for backing up and archiving personal computer files. The trademarked Zip drive was developed and is sold by Iomega Corporation. Zip drives and disks come in two sizes. The 100 megabyte size actually holds 100,431,872 bytes of data or the equivalent of 70 floppy diskettes. There is also a 250 megabyte drive and disk. The Iomega Zip drive comes with a software utility that lets you copy the entire contents of your hard drive to one or more Zip disks. In addition to data backup, Iomega suggests these additional uses:

• Archiving old e-mail or other files you don’t use any more but may want to access someday

• Storing unusually large files, such as graphic images that you need infrequently

• Exchanging large files with someone

• Putting your system on another computer, perhaps a portable computer

• Keeping certain files separate from files on your hard disk (for example, personal finance files)

The Zip drive can be purchased in either a parallel or a Small Computer System Interface (SCSI) version. In the parallel version, a printer can be chained off the Zip drive so that both can be plugged into your computer’s parallel port.

SyQuest makes a similar product and also makes larger and more expensive removable (portable) disk drives that are worth considering if you have a more professional system.

zipping

A Zip drive is something different.

Zipping is the act of packaging a set of files into a single file or archive that is called a zip file. Usually, the files in a zip file are compressed so that they take up less space in storage or take less time to send to someone. There are several popular tools that can be used for zipping files: PKZIP for the DOS operating system, WinZip and NetZIP for Windows, MacZip for Macintosh users, and Zip and UnZip for UNIX systems. The result of zipping is a single file with a ".zip" suffix. After you receive a zip file, you may have to extract and decompress the file by using the same kind of tool that was used to zip the original file.

Most software that you download from the Internet will arrive as a self-extracting zip file. Typically, by double-clicking on a self-extracting zip file, it will automatically extract, decompress, and store the individual files. One of these files is usually called the "setup.exe" file. Double-clicking on this file will cause the software to be installed as a selectable program in your operating system.

Zmodem protocol

Zmodem is an error-correcting protocol for modems. Modems that agree on using the Zmodem protocol send data in 512-byte blocks. If a block arrives and an error is detected, a "NAK" (negative acknowledgement) is returned and the block is resent.

Zoetrope

The Zoetrope (pronounced ZOH-uh-trohp), invented in 1834 by William George Horner, was an early form of motion picture projector that consisted of a drum containing a set of still images, that was turned in a circular fashion in order to create the illusion of motion. Horner originally called it the Daedatelum, but Pierre Desvignes, a French inventor, renamed his version of it the Zoetrope (from Greek word root zoo for animal life and trope for "things that turn.”) A Zoetrope is relatively easy to build. It can be turned at a variable rate to create slow-motion or speeded-up effects. Like other motion simulation devices, the Zoetrope depends on the fact that the human retina retains an image for about a tenth-of-a-second so that if a new image appears in that time, the sequence was seem to be uninterrupted and continuous. It also depends on what is referred to as the Phi phenomenon, which observes that we try to make sense out of any sequence of impressions, continuously relating them to each other.

The visual effect created by a Zoetrope (or Zoopraxiscope) is still used today to create animated GIFs and video display technologies such as streaming video, which essentially create an effect of motion by presenting discrete but closely-related images one after the other.

zombie

In the West Indies, a zombie is a will-less, automaton-like person who is said to have been revived from the dead and must now do the will of the living. There are at least three usages of the term related to computers and the Internet.

1) In the UNIX operating system world, developers sometimes use the term to refer to a program process that has died but hasn’t yet given its process table entry back to the system.

2) On the World Wide Web, a zombie is an abandoned and sadly out-of-date Web site that for some reason has been moved to another Web address. It’s a ghost site that appears to have moved. Zombies contribute to linkrot.

3) In at least one form of denial of service, one or more insecure Web servers are compromised by hackers who place code in each Web server that, when triggered, will launch an overwhelming number of requests toward an attacked Web site, which will soon be unable to service legitimate requests from its users. A compromised Web site that is used as an attack launch point is known as a zombie.

zoo

A zoo is a Web site that holds collections of Internet viruses. These sites may be illegal in certain countries.

Zoopraxiscope

The Zoopraxiscope (pronounced ZOH-uh-PRACKS-uh-scohp), invented by British photographer Eadweard Muybridge and first shown in 1879, was a primitive motion picture device that worked by showing a sequence of still photographs in rapid succession. Muybridge, perhaps best known today for his sequence of photographs of a race horse in motion (which proved for the first time that at top speed all feet leave the ground), studied photography in the early 1860s with daguerrotypist Silas Selleck and later achieved recognition for his photographs of the Yosemite Valley and other scenes of the American Far West. The Zoopraxiscope emerged out of his studies of motion as shown in sequences of still photographs. His 11-volume work, Animal Locomotion, published in 1887, contained over 100,000 photographs. In 1893, he lectured at "Zoopraxigraphical Hall" at the World’s Columbian Exposition in Chicago.

The Zoetrope, along with the Zoopraxiscope and the Thaumatrope, are forerunners of the animated GIF and video display technologies such as streaming video, which essentially create an effect of motion by presenting discrete but closely-related images one after the other.

Zope

Zope (Z Object Publishing Environment) is a Web site builder and application server that uses the idea that it is serving (or "publishing") objects rather than merely providing content that will be added to a Web page. Zope’s proponents believe that it is competitive with site builders and application servers such as ColdFusion and the Netscape Application Server. Zope software is free and uses Open Source code.

Zope programmers describe Zope as "object publishing software." They propose that users are interacting directly with "real objects" rather than with dynamically updated files that are being served. Zope consists of a "publisher" that publishes the objects using Zope’s Persistent CGI protocol; a framework for the folders, files, and images that Zope views as "built-in objects"; an object database; a template for dynamic Web page generation; and Structured Query Language methods and database adapters so that Zope can interact with data in popular database servers, such as Microsoft’s SQL Server. By default, Zope’s object database uses the operating system’s file system to manage data. However, it can also work with relational database management systems. Specifically, Oracle, Sybase, MySQL, and Open Database Connectivity are supported.

Zope was created by Digital Creations and has been used by the U.S. government, U.S. newspapers, and many company Web sites. The software is written in Python, an interpreted, interactive, object-oriented programming language similar to Java, with small pieces written in C for better performance. Web site developers using Zope do not need to use Python, however. Zope runs on all major operating system platforms.

Zulu

Zulu (short for "Zulu time") is used in the military and in navigation generally as a term for Universal Coordinated Time (UCT), sometimes called Universal Time Coordinated (UTC) or Coordinated Universal Time (but abbreviated UTC), and formerly called Greenwich Mean Time. In military shorthand, the letter Z follows a time expressed in Greenwich Time. Greenwich Time, now called Universal Coordinated Time, is the time at longitude 0 degrees 0 minutes—the prime meridian or longitudinal line that separates East from West in the world geographical coordinate system. This line of longitude is based on the location of the British Naval Observatory in Greenwich, England, near London. "Zulu" is the radio transmission articulation for the letter Z.

Traditionally, ship and airplane navigation is conducted using Zulu time. Zulu time is usually expressed in terms of a 24-hour clock using the Gregorian calendar time divisions of hours and minutes.

ZV port

The Zoomed Video port (ZV port) is a technology that supports the delivery of full-screen motion video and multimedia to notebook computers. The ZV port allows special software and a version of the PC Card called a ZV Port Card to provide a separate dedicated, point-to-point bus or path from continuously arriving video signals directly to the display controller so that they do not need to be handled by the main bus or the central processing unit. ZV ports are provided in IBM, Toshiba, and other manufacturers’ notebook computers.

With the ZV port technology, video signals are sent in compressed files using the MPEG standard. The ZV Port Card decompresses the files and sends the data directly to the video frame buffer managed by the display controller. The technology can also be used for capturing images sent to the display from a video camera and storing them on a hard disk. Combining user input from the computer’s regular PCI bus with the video from the ZV port, notebook users can play interactive MPEG-based games.

The specification for the ZV port is an industry standard sponsored by the Personal Computer Memory Card International Association.