X.25 – The first three ITU-defined protocol layers for the DTE/DCE interface at the gateway to a packet-switched network: physical (X.21), link (HDLC), and network. It defines services, including layered protocols and private virtual circuits.
X.400 – E-mail.
X.500 – Address and directory services protocol recommendation. It builds directories on distributed databases so that networks can be divided into distinct domains. The Directory User Agent (DUA) is client software that presents directory options to a user and connects the user to a DSA (Directory System Agent), which exchanges information between user and directory system.
A family of CISC microprocessor instruction sets and architectures, and CPUs designed for them, originated by Intel. Most personal computers use x86 CPUs. The family used to be called 80x86, but with Intel’s Pentium series, the “80” got lost.
The bit size of each specification in the family is the width of the CPU’s internal data bus, i.e., the number of bits that it transfers between elements of the CPU on each system clock cycle. It does not mean the CPU’s memory address bus or external data bus, which can be larger or smaller, and typically use slower clocks as well.
x86-16 – (1978) The 16-bit architecture introduced with Intel’s 8086.
x86-32 – (1985) Also called IA-32 (IA = Intel Architecture) or i386, or, since x86-64, just x86. The 32-bit instruction set and architecture that debuted with Intel’s 80386. It includes features to support backward compatibility with x86-16.
x86-64 – (2000) AMD designed this 64-bit extension of x86, and started calling it AMD64 when they released CPUs based on it in 2003. Intel had bet heavily on their new IA-64, a non-x86 architecture. The PC industry didn’t go for that, and Intel had to license x86-64 and create a variant, Intel 64, to catch up with their smaller rival. Both are fully backward-compatible with x86-32 code.
Explainable Artificial Intelligence. Machine-learning AIs make changes to their own processes, so even their creators don’t know how they arrive at their decisions. An XAI is able to provide explanations of its reasoning.
Extensible Application Markup Language. Microsoft proprietary, XML-based, .NET-aware markup language, intended for user interfaces, i.e., graphics, in the Windows environment. It’s part of WPF.
10-gigabit Attachment Unit Interface, “X” being the Roman numeral 10. Pronounced “zowie”. A 16-pin data bus standard for extending the 72-pin XGMII (see MII), with four 3.125 Gb/s asynchronous, full-duplex serial lines and 8B/10B FEC. See AUI.
Extensible HyperText Markup Language. A standard from the W3C that recasts HTML 4 as a fully compatible application of XML 1.0. It supports all HTML 4 markup tags and attributes, so it looks almost identical to HTML. Many of the differences are just the elimination of flexible practices that HTML tolerated and XHTML doesn’t. See CSS, DTD.
Extensible Markup Language. A subset of SGML introduced in 1998 (v1.0) for use on the Web. It allows users to define and share their own markup tags, hence the “extensible” part. It describes document content, unlike the less flexible HTML, which can describe only presentation.
XML is a meant as a framework for markup languages – in effect, a language for describing languages – not a language itself. However, the content of a XML document can be designed for display as a Web page. HTML pages can incorporate XML code. The recommended way to do this is through a script, e.g. JavaScript, rather than mixing XML with HTML markup. See XHTML.
Extensible Messaging and Presence Protocol. An open, XML-based protocol formalized by the IETF and used for handling messaging traffic across networks.
Extended Memory Specification. A standard for accessing the old MS-DOS high memory area and configuring extended memory. Requires an XMS driver such as himem.sys, which was used in early versions of Windows. See RAM.
Crystal Oscillator. A quartz crystal is a piezoelectric material – that is, applying an electric field changes its shape, and applying physical pressure to it develops an electric field. In a suitable electronic circuit, this interaction between mechanical stress and electric field causes the crystal to vibrate at a precise frequency inversely proportional to its thickness. How a crystal is cut with respect to the crystallographic axes affects its properties. There are a number of cuts, identified with two-letter designators. The most common are AT-cut (the T refers to temperature compensation) and the higher-precision SC-cut.
XML Schema Document. A schema is a description of the structure and content of a XML document. XSD, also called W3C XML Schema (WXS) or XML Schema, is the W3C standard schema language, created to supplement the more limited DTD. Its files use the .xsd filename extension.
Extensible Stylesheet Language. Just as HTML uses CSS to provide separate, easily configurable style documents for Web formatting, XML relies on XSL for the same thing. Its files use the .xsl filename extension.
Cross-Site Scripting. The malicious practice of injecting network code (JavaScript, HTML, Adobe Flash, VBScript, ActiveX) into a Web site to gain unauthorized access and/or to use it as a platform for spreading malware to visitors. To be vulnerable, a Web site must have some way for users to provide input that it then uses to generate output.
Extended. IBM’s 1983 PC-XT, with the Intel 8088 processor, 5¼" 360 kB floppy drive, 5¼" 10 MB hard drive, MS-DOS 2.0, and ISA expansion slots. Clones of this system used the 8086 processor. See PC.