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NOTE:  Items highlighted in RED are defined elsewhere in this Glossary, while items highlighted in BLUE are site links for further information.


U:  U is the standard unit of measure for designating the vertical Rack Mount Unitusable space or height of racks for network computer enclosures.  Sometimes also called a RMU (“rack mount unit”).  1U is actually 1.75 inches, representing the vertical space between the shelves on a rack.  So, if you have a rack designated as 20U, it would have 17.5 inches of vertical usable space for 10 racks. A typical server rack is 42U high.  Equipment for racks is typically measured as 1U, 2U, 3U or 4U high.  See also, rackmount.

UAC:  User Account Control”; the feature in Windows that is designed to protect your computer from unauthorized changes by prompting for permission or an administrator’s password before continuing with the task.  Subject of much debate:  Whether to turn it off or live with the inconvenience.  See Tip #90.

UAS:  “USB Attached SCSI”.  This is a computer protocol and cable type used to move data from USB storage devices and external drives.

UBERGEEK:  An extreme or ultimate geek, more than even the usual geek, characterized by fanatic behavior about technology, often speaking in acronyms and code in a rather arrogant and condescending manner

Uber X logoUber: See, Transportation Network.  This San Francisco startup TN company, founded by Garrett Camp and Travis Kalanick in San Francisco in March, 2009, which connects passengers to drivers using a smart phone app, has gone from zero to a multi-billion dollar valuation and become international (China is its biggest market) in a matter of years.  Riders pay an estimated pre-determined fee calculated by Uber for the service and no additional tipping is required. Charges are processed via credit card of wallet accounts set up with Uber.  There are several categories of vehicles: UberX uses everyday four door cars, but there are upgrades like Black (high end sedans), SUV and Lux (finest vehicles), as well as Taxi and Military, all at additional rates.  Cities which offer Uber Select even provide the option of Teslas or BMWs.   In an effort to wage its campaign against “Big Taxi,” it hired former Obama advisor David Plouffe as a VP and it usually wins in contests against taxis as it is a “ride sharing” service, not a cab that is hailed on the street or at a special stop.  Some states have even passed legislation for this new category of rides, both for and against.  And it has been creative with promotions:  It has partnered with AT&T and Amex, and soon others, for points and rewards.  And it has promotions at times, such as using a DeLorean time machine and ice cream trucks for rides.  But like others (e.g. Lyft, Sidecar), it has suffered extreme backlash from taxis and is still highly controversial, although it’s quickly becoming mainstream and the business model is clearly here to stay.  Uber has also attempted to expand beyond personal transportation, experimenting with flower deliveries, ice cream and Christmas trees.  And in 2014, it introduced a courier service in Manhattan.  On 8/19/14, Uber introduced a trial service in Washington, DC, offering on-demand delivery of medicine, toiletries and other drug store products via “Uber Corner Store”.  You toggle a “corner Store” option in the Uber app and get a link to a list of items available for purchase.  Then an Uber driver calls to take your order and, upon delivery, the purchase is charged to your Uber account.  The initial delivery zones, however, will target only wealthy parts of the city.  All of this is predicated on the (original) Uber promise to “deliver [cars, or whatever] within five minutes”.  Since then, the five minute promise has been abandoned, but they’re pretty fast.  Of late, it’s impossible to keep up with the Uber saga - trying to compete with cabs, Lyft and others, they’ve reduced driver compensation, causing lawsuits against them.  And they’re constantly trying new things like “carpooling” and UberEATS food delivery (kinda like Grubhub) to see if then can get more customers.  FUTURE:  In 2016, Uber has been experimenting with self-driving Volvos in Pittsburgh and also trucks.  If successful, it may be rolled out throughout the U.S. 

Ubuntu logoUBUNTU: One of the more popular distros of Linux.  Just like Android names its versions after foods, Ubuntu names its versions after critters, 19 so far. Currently up to Ver. 13.10, Saucy Salamander.  Also is developing Ubuntu Touch for mobile and pad apps.  The logo represents three people holding hands and looking upward.  See Linux.

UC:  Unified Communications.  Used with reference to businesses, this refers to the software and hardware packages which purport to combine telephones, web conferencing, messaging, VoIp and the like under a single centralized system.  Kind of like “convergence” for businesses. (See, for example, Avaya, Cisco, IBM, Microsoft Office Communications Server 2007.) Basically, UC allows enterprise employees to use various communication methods without becoming isolated from other employees not using the same exact tools.

UCIF:  Unified Communications Interoperability Forum.  Established in 2010 with initial members HP, Juniper, Microsoft, Logitech/LifeSize Communications and Polycom, it is a nonprofit organization for the purpose of creating open standards for communications equipment.

UDOO logoUDOO: A Raspberry pi mini-pc with an ARM i.MX6 processor that can run either Android or Linux, which has an Arduino DUI-ARM compatible board embedded.  All open source hardware and software.  Great for modding projects or learning basic electronics and computers.  Click HERE for the site.  See also Raspberri pi, Modding, Hacking, Arduino.

UDID:  Stands for Unique Device Identifier.  THIS IS ONLY APPLICABLE TO APPLE DEVICES.  It is a 40 character sequence that is specific to iPods, iPhones, etc, much like a serial number.  It’s used by Apple on iTunes to give you permission to install apps on your devices.  You can find your UDID, using this App.

UDP:  User Datagram Protocol.  Like its cousin TCP, UDP is another protocol that supports network applications that need to transport data between computers.  The difference is that UDP does not divide the message into packets (“datagrams”) and instead trusts at the software at the receiving end to take care of the verification, so it is faster.  Users with small messages will use TFTP (“Trivial File Transfer Protocol), which uses UDP.

UEFI:  BIOS isn’t the only game in town.  Some 30 years after the invention of the first DOS PC, Unified Extensible Firmware InterfaceUEFI logo is a faster and newer UEFI on ASUSalternative to BIOS. A standard created by over 140 technology companies, it is firmware originally introduced by Intel with its Itanium chips that introduced new ways of booting an O/S that is distinct from the commonly used "MBR boot code" method followed for BIOS systems. [See File System.]  UEFI, which can be booted alone or with BIOS, can reside on a disk or EPROM, and does not include POST (which isn’t really necessary any more since most peripherals have their own Windows device drivers anyway) or initial setup (CPU & memory), which can be handled by other add-on software.  The big advantage is it’s resistance to malware, particularly rootkits, as the UEFI “secure boot” option uses PKI to validate the software before a full boot to Windows can run and cause damage the computer.  And, since there is no MBR, there can be no MBR viruses.  It also starts up and recovers from hibernation much faster and supports drives larger than the 2.2Tb limit of BIOS, as well as 64-bit systems.  This may create some problems with Linux users, but it appears that they can either turn off UEFI secure boot, or customize it.  UEFI comes standard with Windows beginning with Windows 8 and all 64-bit systems since then; it’s what enables the “fast start” feature.  See also, firmware, FAQ #72 and FAQ #53.

UFS:  Unix File System.  See File System.

UI:  User Interface.  The point at which interaction between human and machine converge.  In a computer, the UI is generally the information on a screen which a human manipulates to accomplish a task.  Example:  In Win8, the “tiles” are the UI in DOS, the command line. The easier the UI, the more satisfying the user experience (“UX”). Tiles, for example, are far easier to manipulate than commands.

ULTRA-WIDE BAND/ULTRABAND:   Formerly known as “pulse radio”.  A radio technology used for short range, high bandwidth communications.  It consumes very low energy and uses a large portion of the radio spectrum, much like spread spectrum technology.  It was pioneered by Robert A. Scholtz.

UMA:  Unlicensed Mobile Access.  The technology that lets VoIP run on top of conventional GSM cellular service, or SIP, the increasingly popular, non-proprietary standard for Internet-based voice and video calls.

UML:  Unified Modeling Language.  This is a language that is used to write the “blueprint” for computer systems, which has quickly become the de-facto standard for object-oriented software.  It is a language, not a method or procedure.

UMPC:  Refers to a “Ultra Mobile Personal Computer”.  Defined as a computer which has a screen between 5 and 7 inches wide.  Sometimes called a “netbook” Smaller than a laptop, generally with a solid state drive (SSD) and somewhat limited capabilities.  See, for example, the Asus Pceee (basic; under $400); also Fujitsu U810 (tablet, movable screen, 5.5 hrs. battery life; $999). UMPCs usually run Windows; alternatively, Mobile Internet Devices (“MIDs”) run other operating systems, like Linux.  IDC estimates that this market will be worth about $3 billion by 2012; look for use of the Intel Atom Z-520 chip (1.33Ghz,533Mhz front-side bus, 512Kb Level 2 cache) in more of these computers, pushing the envelope for battery life and power. See Laptops.

UMTS:  Universal Mobile Telecommunications System.  A third generation (“3G”) digital mobile telecommunications standard which enables digital mobile phones to function in GSM networks as well as UMTS, permitting reception in areas where UMTS may not yet be available.  UMTS is specifically designed for high-speed data transfer and is “Internet ready” as well as interference tolerant and, because it is based on CDMA and spread spectrum technology, boasts extraordinary voice quality, high data rates and huge network capacity, achieving a maximum data rate of up to 384 kilobits per second, making mobile multimedia applications a reality.

UNICODE: A computing industry standard for the consistent encoding of text expressed in most of the world’s writing systems, currently about 109,000 characters.


UNIFIED COMMUNICATIONS: With UC, multiple modes of business communications are seamlessly integrated.  UC is not a single product, but a collection of elements that include call control and multimodal communications, presence, instant messaging, unified messaging, speech, conferencing, collaboration tools, and business process integration.  UC is sometimes confused with unified messaging, but is actually distinct.  UC refers to both real-time and non-real-time delivery of communications based on the preferred method and location of the recipient.  Unified messaging systems cull messages from several sources (such as email, fax and voice mail), but holds these messages only for retrieval at a later time.  UC allows for an individual to check and retrieve an email or voice mail from any communication device at any time, expanding traditional voice mail services to data communications and video services.

UNITY: One of the more popular shell (desktop interface) program used by Ubuntu Linux.  See GNOME for more.

UNIVAC:  World’s first commercial electronic computer, invented circa 1960.  Took up an entire room, ran on vacuum tubes.  See also, ENIAC, Grace Hopper.

UNIVERSAL APP:  See Windows Universal App.

Unix logoUNIX:  (Originally spelled “Unix,” now just ”unix” to convey the open source idea rather than a branded programming language.)  A computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs (Ken Thompson, Dennis Ritchie (who also developed “C”) & Douglas McIlroy) designed to network multiple stations connecting to a central hub or hubs in what is known as “star” topology (incidentally, the same basic structure as the Internet itself).  For a long time Unix was actually the prevalent operating system in use, and is still used widely in scientific and commercial networks, and most of the Internet, including much of the older Bell telephone systems.  Due to monopoly laws, AT&T wasn’t allowed to sell Unix, so it licensed it to many others which made their own variants.  Unix now has many derivations (freeBSD, openBSD, Slackware, HP-UX, etc.), mostly commercial, but one popular version was created by the University of California at Berkeley, known as “BSD” (for “Berkeley Software Distribution”).  As opposed to Unix knock-offs with modifications, in 1991, Linus Torvolds created a competing operating system from scratch, using information from the GNU project at MIT, named Linux.   Linux mimicked Unix, the difference being that it was written from scratch and would remain open forever.  How does Apple’s OS X fit in here?  Well, just as Linux adopted GNU’s tools but not its kernel, Apple did the same thing with Darwin (the Unix part of OS X), which adopted the tools of BSD Unix but rewrote its kernel from scratch. So Unix, Linux and OS X are loosely related to each other.  REMEMBER:  Unix time begins on January 1, 1970 (00:00:00) so, if you set many devices to that date or before, it will effecively brick the device.

UPGRADE VS. UPDATE: An update (sometimes called a “patch”) is usually meant to correct a software bug in a program or add some additional support or changes to an existing program, and is usually downloadable for free.  An upgrade, on the other hand, usually does not involve bug correction or additional features but instead involves the advancement of the original program to an entirely different level (as from an OEM version to a paid version of a program), usually by purchasing a paid and completely new issuance of the program.

UPLOAD: The reverse of download.  The transfer of data from a computer (usually a PC or smaller computer) to a larger computer or network.  For example, when you post photos to eBay, you’re uploading them to the site.  Similarly, when you send files across the network, you are uploading them.

UPnP: Stands for Universal Plug and Play. A set of protocols used by many network devices such as routers automatically open certain (router) ports so that devices like routers, computers and printers  can interconnect and communicate over the Internet [as opposed to manually opening those ports through the router software configuration].  For example, when Windows built-in “network discovery feature” seeks out devices to connect to, it uses UPnP.  But many security experts don’t like UPnP, or even recommend disabling it, because it doesn’t use any form of authentication, therefore allowing unauthorized devices to connect to the network.

UPS:  Uninterruptible Power Supply.  This is a power supply (essentially a “battery”) which provides continuous, reliable power during a loss of input power for a period of time.  The length of time and amount of power depends on the specifications of the power supply itself, usually expressed in “joules” (sensitivity) and “clamp time” (speed of reaction).  Often the power supply has surge suppression built in to some or all of the power outlets so that, in addition to battery backup, they can address a wide variety of electrical-related issues such as short-term voltage sags (“undervoltage”), long-term periods of undervoltage, short-term voltage spikes (“overvoltage”), noisy power sources, etc.  In addition, some UPSs have Master/Controlled outlets, which can be enabled to automatically turn off items plugged in to it when not drawing current (such as printers), to save electricity.  Primary considerations for UPSs are capacity (the maximum amount of power a UPS can handle) and runtime (the length of time it will continue providing backup power in the event of an outage).

There are several types of UPSs:  A UPS type with built-in line sensing abilities to regulate high and low voltage levels which activates an inverter when power loss occurs, causing the system to switch to battery power is called  “line-interactive”.  The highest type of UPS protection level is provided, however, by an online UPS, where the inverter is online and operates constantly to eliminate incoming surges and low and high voltage issues while delivering clean power. Less effective and less expensive is a standby UPS system, where power runs through the surge suppressor to the connected equipment and the UPS switches to battery backup power, reverting to AC power when power returns.  For residential computer users, there are also “smart strips” which shut down the standby power on many electronics devices even when they are turned off (the “always-on” computers, TVs and the like) which can consume lots of power, the use of which can materially reduce your electric bill each month.

In server rooms of larger systems, additional considerations (such as IGBT (insulate-gate bipolar transistors) and DSP (digital signal processors), both of which provide for true online “double conversion” (which converts AC power to DC and then back to AC) must be considered).  They go further than simple residential “line interactive” appliances to online and standby models used in larger installations.   In addition, the UPS may have software which shuts down the open computer programs and saves any unsaved data, prior to the expiration of the battery power itself.  UPSs are claimed to be more effective than surge protectors for protection against lightning, power surges, brownouts, blackouts, voltage fluctuations, power spikes and line noise, because the battery offers additional protection, in addition to keeping the computer running.  But see the discussion about printers and UPSs in TIPS.  See also, flywheels.

UPSTREAM: Applies to the speed of an internet connection when uploading a file from your computer to another computer over your internet connection.  These speeds are typically lower than downstream transfers over the same network.

URL:  “Uniform Resource Locator”.  Means an Internet “address”.  This is a string of characters to identify a page of information on the internet.  It’s what you see on the “address bar” of your browser.  The URL is divided into two parts:  The first part identifies the protocol to use to visit the site.  The normal protocol is “http://” which means “hypertext transfer protocol”, which identifies the majority of the World Wide Web (“www”) pages written in HTML or Hypertext Markup Language.  The second part of the URL specifies either the domain using English characters (i.e. “ or or numbers known as the IP (“Internet Protocol”) address (e.g. 123.456.789.000 - always up to 4 sets of up to three digits separated by points).  Most sites have both a numbered IP address and a domain address.

USB: Click HERE.


USENET: One of the largest bulletin board services (“BBS’s”) of the 1990s, before chat and the Internet became popular.


USER ERROR:  It’s not the hardware or the software, either.  It’s the way the operator is using the computer.  Some adjustment must be made to correct the problem. 

UTIL:  My very own acronym.  It means “You Touched It Last”. Often, computer repair techs get a callback after servicing computers, sometimes concerning some unrelated computer or a peripheral on or off the network, that has mysteriously developed problems.  Usually, the client’s explanation is that you touched the system last, therefore any problems which occur for a short period thereafter must be your fault.  And, usually, you have to fix the problem free of charge as a warranty item if you want to keep that client’s business.

UTILITY:  A software application which performs a special function for an operating system or its files.  For example, ScanDisk is a Windows utility which checks the hard disk drive for errors.  Anti-virus and firewall programs are also types of utilities.  Essentially, utilities effect the performance of the operating system, not the application programs themselves.

UTM:  Unified Threat Management.  Software that seeks to comprehensively block malware and network threats through features such as a firewall, antivirus, antispam, intrusion prevention, VPN, access policy enforcement and other practices, usually installed on a corporate managed appliance.

UTP:  Unshielded Twisted Pair cabling, meaning cables that consist of pairs of unshielded copper wire twisted together.  This is the most common type of wiring used for telephone and computers.  UTP is less expensive to manufacture because it is unshielded, and it achieves its shielding by being twisted together in pairs.  For more discussion, see Ethernet.


UWB:  UltraWideBand.  This is a low-power, high-speed wireless technology that transmits large amounts of data, such as digital files, over a wide spectrum of bandwidth for a short distance.  The technology is most often compared to Bluetooth, but the advantages are that is uses speeds of up to 480Mpbs at distances as much as 3 meters and 110Mpbs at 10 meters, UWB’s performance rate is estimated at 100 times the speed of Bluetooth and twice that of Wi-Fi and, because it uses a larger chunk of bandwidth than either Bluetooth or Wi-Fi, it yields much less multipath interference while it can carry signals through typical wireless obstacles, such as doors and walls.

UX: Short for “User Experience”.  Basically, this encompasses the entire process of interaction between the consumer or end user and an organization, from initial contact through advertising and web through selection, payment, delivery, actual use and possible dispute resolution.  It also extends to the quality and features of the product itself.  The goal is that the user be delighted with the product and service from beginning to end, hence the “experience”.  This is, then, far more broad than the mere user “interface” (“UI”), whether that is through personal contact or computer interaction, because that is only one part of the “experience”.  In an enterprise, the people who are responsible for UX, are often titled “CXOs”.   These are the people, for example, who determine how easy it is for computer users to use software or hardware to achieve the desired result.  For example, UX folks (like Raluca Budiu of the Nielsen Norman Group) reviewed the Win8/RT program and the Microsoft Touch Mouse to see and report about how they performed.  See also, CXO.





























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