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A glossary of terms important to IBM mainframe machines
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z misc.
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X.400: Series of draft international standards for message handling systems, including e-mail, fax, and image/graphics transmission. Ratified by the ITU-T in 1984. X.400 support is available from IBM through IBM Interchange Services for e-business, GTMOSI, OSME, X.400 Connection, X.400 MTF, IPMS, ONDS, and on the iSeries 400.
X.400 Connection: IBM z/OS and z/VM software for handling IBM format messages, converting them to X.400 and routing them across an EDI1 system through OSME. Supports PROFS, DISOSS, OfficeVision, PS/CICS. Withdrawn 1995.
X.400 MTF: X.400 Message Transfer Facility. First product announced by IBM to span all seven layers of the OSI model. Allows user applications running on z/OS systems to participate in message handling systems with other vendors’ systems that are X.400 compliant. Part of ONDS, withdrawn July 1995.
X/Open: Originally a group of vendors (including IBM) which joined up to set up standards (particularly for Unix). Unlike UII and OSF, X/Open tried not to be partisan in the Unix battle. October 1993, Novell, the then owner of Unix, handed control of the Unix standard lock, stock, and barrel to X/Open, which then tested and branded implementations claiming to be Unix systems. November 1995, X/Open started cozying up to the OSF with the declared aim of making the two organizations appear as two sister divisions of a virtual corporation. The Open Group was the result. See also XPGn.
XA2: An X/Open standard for distributed transaction processing which defines the interface between a database and a TP monitor. XA describes a standard protocol for transaction co-ordination, commitment, and recovery between a transaction manager and one or more resource managers (such as databases).
XAMO: XA Migration Option.
XCF: Cross System (coupling) Facility. Software, introduced in MVS/ESA SP4, which allows programs to communicate channel-to-channel, peer-to-peer, across a sysplex – i.e., it’s the basic sysplex-enabling bit of z/OS. XCF supports program communication, and sends program status and signal information between z/OS system images in a sysplex.
XDR: External Data Representation.
Xenix: A Unix-alike developed by Microsoft. At one time available from IBM for the PC. SCO (Santa Cruz Operations, now part of Caldera International) ended up with Xenix, but have put all their efforts behind UnixWare, which they acquired from Novell.
Xerox: Everybody else knows them from their photocopiers, but computer people are just as likely to think of Xerox PARC, founded in 1970, and still in operation. There, the mouse, the GUI, client/server architecture, laser printing and the Ethernet/LAN were all born. In a company with executives totally focused on paper and business machines, it took young outsiders like Steve Jobs and Bill Gates to visit PARC and take away the ideas for their own companies: Apple and Microsoft. Xerox did try. Their D series computers pre-empted the PCs of the 1980s by a decade. And a Xerox word processor had a paper shaped monitor that displayed an entire page at once, but no one would pay more the $10,000 per station for it. Today, few remember Xerox was ever in the computer field at all.
XL Fortran: AIX1 FORTRAN compiler that supports the Open MP FORTRAN API, SMP3, direct manipulation of the floating point status and control register, 64-bit architecture, asynchronous I/O, debug memory routines and the FORTRAN 95 standard.
XML: eXtensible Mark-up Language. A subset of SGML and a W3C standard. Widely accepted as a replacement for traditional EDI1 for exchanging data between applications over the Internet. Unlike HTML, XML is self-defining in the sense that, when you look at an XML file, most of what you see are field names in XML tags followed immediately by a field value.
X-off: Transmitter off.
X-on: Transmitter on.
XRF: eXtended Recovery Facility. Feature available with DB2, IMS1 and CICS, providing vastly increased availability for mission-critical applications. XRF creates a mirror system synchronized with the main system; the mirror image can take over immediately in the event of a failure in the primary system (in many, but not all, cases). Can also be used for planned machine maintenance by purposely switching to a backup system while working on the main system. See also mirroring.
XSL: eXtensible Stylesheet Language. A W3C standard used with XML. XSL comprises a language for transforming XML documents into another markup language format, together with a vocabulary for specifying formatting semantics. Commonly used to convert XML data to HTML for presentation in a Web browser environment. An XSL processor is one of the suite of XML application enablers delivered with OS/400.
XSSO: X Single Sign-On.
XSSO/PAM: X Single Sign-On/Pluggable Authentication Mechanism.
Xstation: Low-priced family of X-Windows terminals for attachment to a LAN (Ethernet or TRN). Sold for DTP1, CASE1, low-end CAD, and the like – not high-performance CAD. Based on technology bought in from X-terminal specialist Network Computing Devices. Early 1996, IBM stopped selling the things under its own name, and handed the business back to Network Computing Devices.
xterm: A terminal emulation program for the X Window System. Allows the user to have several different invocations of xterm running at once on the same display, each of which provides independent input and output for the process running in it.
X-Terminal: A type of terminal developed in the Unix world which provides a GUI type environment (usually X-Windows) without the need for a programmable workstation. The X-Terminal is responsible solely for painting the screen – a host decides what to paint (Note that the workstation is called the server, and that the host is called the client, which is the opposite of what everybody else (including common sense) says). The X-Terminal typically has no disk, but has a lot of memory (at least 500KB, and possibly 2MB) and a specialized processor. Sounds like a good idea but the problem then was that, in some applications, each X-Terminal seemed to need 2MB in the host as well, if it’s to perform adequately. By the mid 1990s the idea was going rapidly out of fashion. Early 1996 IBM passed all of its X-Terminal business over to Network Computing Devices. See also Xstation.
XTP: Xpress Transport Protocol. Data transmission protocol for high-speed links (over 75Mbps) that reached its peak of popularity in the early 1990s.
X-Windows: Software system for creating GUIs on X-Terminals. Developed originally at MIT (as part of the DEC/IBM/MIT Project Athena) but picked up by the wider Unix community. Note that X-Windows is not an actual GUI, it is a set of standards and tools from which GUIs can be specified and built. Has been an influence on the Motif GUI being developed by the OSF. IBM was involved in the evolution of X-Windows through the MIT X Consortium which provided a forum for discussion of the standard. See also X-Terminal, X Window System.
X Window System: A specification for device-independent windowing operations on bit map display devices. It was developed initially at MIT as part of the DEC/IBM/MIT Project Athena and is now a de facto standard supported by the X Consortium. X uses a client/server protocol, the X protocol. The server is the computer or X terminal with the screen, keyboard, mouse and server program and the clients are application programs. Clients may run on the same computer as the server or on a different computer, communicating over Ethernet via TCP/IP protocols.