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Universal algebra

The model theory of first-order equational logic.

Last updated: 1997-02-25

Universal Asynchronous Receiver/Transmitter

(UART) An integrated circuit used for serial communications, containing a transmitter (parallel-to-serial converter) and a receiver (serial-to-parallel converter), each clocked separately.

The parallel side of a UART is usually connected to the bus of a computer. When the computer writes a byte to the UART's transmit data register (TDR), the UART will start to transmit it on the serial line. The UART's status register contains a flag bit which the computer can read to see if the UART is ready to transmit another byte. Another status register bit says whether the UART has received a byte from the serial line, in which case the computer should read it from the receive data register (RDR). If another byte is received before the previous one is read, the UART will signal an "overrun" error via another status bit.

The UART may be set up to interrupt the computer when data is received or when ready to transmit more data.

The UART's serial connections usually go via separate line driver and line receiver integrated circuits which provide the power and voltages required to drive the serial line and give some protection against noise on the line.

Data on the serial line is formatted by the UART according to the setting of the UART's control register. This may also determine the transmit and receive baud rates if the UART contains its own clock circuits or "baud rate generators". If incorrectly formated data is received the UART may signal a "framing error" or "parity error".

Often the clock will run at 16 times the baud rate (bits per second) to allow the receiver to do centre sampling - i.e. to read each bit in the middle of its allotted time period. This makes the UART more tolerant to variations in the clock rate ("jitter") of the incoming data.

An example of a late 1980s UART was the Intel 8450. In the 1990s, newer UARTs were developed with on-chip buffers. This allowed higher transmission speed without data loss and without requiring such frequent attention from the computer. For example, the Intel 16550 has a 16 byte FIFO. Variants include the 16C550, 16C650, 16C750, and 16C850.

The term "Serial Communications Interface" (SCI) was first used at Motorola around 1975 to refer to their start-stop asyncronous serial interface device, which others were calling a UART.

Universal Character Set

<character, standard>

(UCS, ISO/IEC 10646) A 1993 ISO and IEC standard character set, also known as "Universal Multiple-Octet Coded Character Set".

UCS comes in a 16-bit variant called UCS-2 and a 32-bit variant called UCS-4, which is composed of 16-bit UCS-2 "planes". So far only one 16-bit plane has been defined, which is known as the Basic Multilingual Plane.

The implementation of UCS is still in its infancy, though some moves, such as the Java language defining a character to be 16 bits, are suggestive.

[Relationship with Unicode?]

Last updated: 1997-07-04

Universal Communications X

<communications>

(UCX) A software implementation of the ubiquitous TCP/IP suite of communications protocols for Digital Equipment Corporation's OpenVMS operating system.

Users of the UCX product can connect to heterogeneous networks to access and download files, send electronic mail, run and develop applications, and monitor activity.

"Software Product Description, DIGITAL TCP/IP Services for OpenVMS, Version 4.2",.

Last updated: 2000-12-15

Universal Computer Protocol

<communications, protocol>

An earlier form of External Machine Interface (EMI).

Last updated: 2007-09-10

Universal Debugger

<tool, parallel>

(udb) KSR's interactive source level debugger for serial and parallel programs written in KSR, Fortran, KSR C and KSR1 assembly language.

Udb is a source level debugger for testing and debugging serial and parallel programs; it is compatible with GDB and dbx. The user can direct udb either by typing commands or graphically through an X-based window interface; the latter provides simultaneous display of source code, I/O and instructions. For parallel programs, operations can be carried out per-thread.

Home.

Last updated: 1995-05-07

Universal Description, Discovery, and Integration

<standard, protocol>

(UDDI) The service discovery protocol for Web Services through which companies can find one another to conduct business. This standard was unveiled by Ariba, IBM, Microsoft, and 33 other companies in September 2000.

Last updated: 2002-06-28

Universal Disk Format

<storage, standard>

(UDF) A CD-ROM file system standard that is required for DVD ROMs. UDF is the OSTA's replacement for the ISO 9660 file system used on CD-ROMs, but will be mostly used on DVD. DVD multimedia disks use UDF to contain MPEG audio and video streams.

To read DVDs you need a DVD drive, the kernel driver for the drive, MPEG video support, and a UDF driver. DVDs containing both UDF filesystems and ISO 9660 filesystems can be read without UDF support.

UDF can also be used by CD-R and CD-RW recorders in packet writing mode.

Last updated: 1999-09-01

Universal Naming Convention

<networking>

(UNC) The type of file system path used in Microsoft Windows networking to completely specify a directory on a file server.

The basic format is:

 \\servername\sharename

where "servername" is the hostname or IP address of a network file server, and "sharename" is the name of a shared directory on the server. This is related to the conventional MS-DOS "C:\windows" style of directory name. E.g.

 \\server1\dave

might be set up to point to

 C:\users\homedirs\dave

on a server called "server1".

It is possible to execute a program using this convention without having to specifically link a drive, by running:

\\server\share\directory\program.exe

The undocumented DOS command, TRUENAME can be used to find out the UNC name of a file or directory on a network drive.

Even Microsoft don't know whether UNC stands for "Universal Naming Convention" or "Uniform Naming Convention", both appear on their website, sometimes withing the same document, but with a preference for "Universal".

Last updated: 2008-12-09

universal quantifier

quantifier

Universal Resource Identifier

<web>

(URI, originally "UDI" in some WWW documents) The generic set of all names and addresses which are short strings which refer to objects (typically on the Internet). The most common kinds of URI are URLs and relative URLs.

URIs are defined in RFC 1630.

W3 specification.

Last updated: 1997-07-16

Universal Resource Locator

Uniform Resource Locator

Universal Serial Bus

<hardware, standard>

(USB) An external peripheral interface standard for communication between a computer and external peripherals over an inexpensive cable using biserial transmission.

USB is intended to replace existing serial ports, parallel ports, keyboard, and monitor connectors and be used with keyboards, mice, monitors, printers, and possibly some low-speed scanners and removable hard drives. For faster devices existing IDE, SCSI, or emerging FC-AL or FireWire interfaces can be used.

USB works at 12 Mbps with specific consideration for low cost peripherals. It supports up to 127 devices and both isochronous and asynchronous data transfers. Cables can be up to five metres long and it includes built-in power distribution for low power devices. It supports daisy chaining through a tiered star multidrop topology. A USB cable has a rectangular "Type A" plug at the computer end and a square "Type B" plug at the peripheral end.

Before March 1996 Intel started to integrate the necessary logic into PC chip sets and encourage other manufacturers to do likewise. It was widely available by 1997. Later versions of Windows 95 included support for it. It was standard on Macintosh computers in 1999.

The USB 2.0 specification was released in 2000 to allow USB to compete with Firewire etc. USB 2.0 is backward compatible with USB 1.1 but works at 480 Mbps.

usb.org.

Last updated: 2004-01-31

universal thunk

<programming, operating system>

A software mechanism allowing a Windows 3.1 application to call a 32-bit dynamically linked library (DLL) under Win32s.

The Windows 3.1 application which wants to call an entry in a 32-bit DLL instead calls a corresponding entry in a 16-bit DLL. The programmer must also include code to detect whether the 32-bit DLL is loaded. A 32-bit EXE loads the 32-bit DLL.

Universal Time

<time, standard>

(UT) The mean solar time along the prime meridian (0 longitude) that runs through the Greenwich Observatory outside of London, UK, where the current system originated. UT is tied to the rotation of the Earth in respect to the fictitious "mean Sun".

Greenwich Mean Time (GMT) was measured from Greenwich mean midday until 1925 when the reference point was changed from noon to midnight and the name changed to "Universal Time".

There are three separate definitions, UT0, UT1, and UT2, depending on which corrections have been applied to the Earth's motion. Coordinated Universal Time is kept within 0.9 seconds of UT1, by addition of leap seconds to International Atomic Time.

Last updated: 2001-08-02

Universal Time Coordinated

<time, standard>

An incorrect term for Coordinated Universal Time.

Last updated: 2001-08-01

Nearby terms:

Universal algebra ♦ Universal Asynchronous Receiver/Transmitter

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