"The Atari A to Z" by Mark S Baines Copyright (c) 1998 Mark S Baines All Rights Reserved YOU MUST READ "READ_ME.NOW" BEFORE YOU LOOK AT ANY OF THIS FILE ***************************************************************************** U UART Universal Asynchronous Receiver Transmitter. An integrated circuit device performing interfacing functions between a bit-parallel bus and a bit-serial asynchronous device, such as a modem. Typical functions include bit- parallel/bit-serial conversions, parity generation and checking and transfer synchronization. See USART. ULA Uncommitted Logic Array. A logic array chip that can be programmed in a stage of its manufacture to specific requirements in consultation with a customer. The chip is normally made leaving the last few stages incomplete which are added by the customer when programming it using specialist software and hardware. The customer can test out the device until the final specifications are agreed on when the chip can then be committed to an ASIC. Unary Consisting of a single entity or performed with a single operand. See Monadic. Unary operator An operator that specifies an operation on or with a single operand, such as the '-' sign to negate a value, e.g. -3. Unconditional jump Also, unconditional branch or control transfer. A transfer of control from one program sequence to another that always takes place when a particular instruction in the first sequence is executed or with initiation from an external source, such as an interrupt routine. Undefined Not specified or known to an operating system. Underflow In an arithmetic operation, the condition in which the result is too small to be represented by the method in use. Also, where a data item contains less than the specified number of digits or characters. Underline A line placed underneath printed characters to emphasize them. Although this is common on typewritten and word processed print material (mostly because of the lack of other means of emphasis), it is undesirable in DTP and typeset material and not used by professionals. Undo A program function that reverses the last user operation with the aim of correcting a mistake. Programs that use it constantly place whole or part of the data being operated on in a buffer so that it can replace any alterations made to it. Some programs will have more than one buffer, so that the user can undo their actions by several steps. Undo key A program defined key, often associated with an undo function. It is unused by TOS but Atari recommend that it should be used for any program Undo operation. Unformatted capacity The capacity of a magnetic disk without allowing for the data and other marks written to the disk when formatted. A double density double-sided floppy disk has an unformatted capacity of around 1 Mb but this falls to 726,016 bytes (depending on the format) when formatted. Unformatted disk A magnetic disk which has not been initialized or formatted for use. In this state it is completely unusable. Unidirectional The printer operation of only printing from left to right along a line. Also, a data transfer along a data bus in one direction only. Unintelligent Also, dumb. A term applied to a terminal of a multi-user system that has no processing capability and/or memory itself. It basically acts as an input/output to the main computer. The term may also apply to other devices, such as Atari's laser printers which have no processor or memory unlike all other laser printers. Unipolar In a circuit, using either positive or negative pulses, but not both. Uniprocessor A computer with only one processor for executing program instructions, such as the Atari range and most other microcomputers. Unit separator ASCII character 31, used to delineate units of data in some data transfer, storage or transmission systems. UNIX (UNICS) UNiplexed Information and Computing Service. A real-time multi-user operating system developed by Bell Laboratories capable of running on most 16- or 32-bit computers. Although traditionally designed for mainframes and minis it is now found on microcomputers but has a reputation for being harder to use than MS- DOS and extremely greedy on memory and storage space. It is, however, much more versatile. It has close ties with the C programming language. The TT is capable of running UNIX and the ST-Falcon range can run UNIX clones, such as MINIX and LINUX. See TT UNIX Workstation. Unpack To expand packed or compressed data to its original form. Unprintable character A character that has no agreed graphic representation, such as a carriage return or line feed character. Unrecoverable error An error that results in loss or corruption of data or code, not cleared by the operating system's recovery facilities. Unsigned number A number that has no '+' or '-' sign and assumed to be positive. An unsigned 16-bit integer will have the range 0 to 2^16 whilst a signed 16-bit integer the range -2^15 to 2^15. Unstable Subject to random or unpredictable changes. Update To create a new generation of a master file by incorporating into it changes to reflect the current status of its data, by the deletion, addition and modification of its records. Also, to make corrections and changes to instructions, manuals, programs etc. to reflect their current status. An update normally results in a new version number to signify the change. Upgrade To add new hardware or software to improve the performance or extend the capabilities of a system. Uplink The path on which transmissions are sent from an earth station to a communications satellite. Up-load The process of copying program or data files from a local computer to the main computer or server in a communications network. Upper case The capital letters of a font. UPS Uninterruptable Power Supply. A power supply that can transfer the load to a battery in the event of a failure of the mains source, thus enabling a proper power down of the system without data loss. Up time The time a computer or other functional unit is operational. Upward compatible A term applied to software for one range of computers that will run on later models from the same manufacturer. URL Universal Resource Locators. A standard for referring to any document or service on the Internet associated with WWW. The syntax is: protocol://hostaddress[:portnumber]/pathname such as: http://www.stsd.demon.co.uk/linnhe.html. See WWW, HTTP. USART Universal Synchronous/Asynchronous Receiver Transmitter. An integrated circuit interface device to provide serial-parallel data conversion between a microprocessor and a modem and which can handle both synchronous and asynchronous transfers. On the Atari ST, the functions of a USART are performed by the ACIA and MFP 68901 chips. USENET US Education NETwork. The USENET is an informal world-wide group of systems that exchange news in the form of newsgroups which are similar to the echoes or conferences in a bulletin board network. The USENET is not a computer network and it does not require the Internet although the Internet has become the primary means of access to it. The USENET is a set of voluntary rules for passing and maintaining newsgroups, the messages within them and their structure. It is also the volunteers who use and respect those rules. There are over 8,000 different newsgroups, with at least eight being specific to Atari computers, two of which carry UUENCODEd encrypted files. User A person or organization using a particular computer system. Also, a program that accesses a unit of data. User address space Also, user area. That part of main storage available to a user's programs. See TPA. User area See User address space. User attribute file A file containing information on all authorized users of a multi-user computer system, such as name, account number, password and access levels. User-defined A function or meaning specified by a user and not by the manufacturer or programmer, such as a user-defined key. User-friendly A term applied to software and hardware that is easy to operate and has good error recovery facilities. Such programs normally have a conversational style, sensible defaults and have plenty of escape routes for the user. User group A group of individuals with a common interest set up for the purpose of exchanging information and experience, such as 'The Association of C and C++ Users'. User identification A character string that uniquely identifies a user to the operating system of a multi-user computer for purposes of determining access rights, resource entitlement and accounting. It would normally be that person's name or a derivative of it, such as msbaines. Once identified a system would also require a unique and secret password from the user to confirm that person's identification. User mode The mode in which the central processing unit is executing instructions of a user program, one of the two modes of operation of a MC680x0 CPU. See Supervisor mode. User profile See User attribute file. User program An application program owned by a user rather than a systems program. User terminal A multi-user computer terminal in a user's premises. USRT Universal Synchronous Receiver Transmitter. An integrated circuit device designed to perform series-parallel conversion and timing of synchronous bit- serial data in a microcomputer. Utility A system software program that performs, usually, one particular task generally of a system 'housekeeping' nature. Such utilities may be disk formatters, disk copiers, a file undelete program, a clock, calculator etc. UUCP Unix to Unix Copy Program. A UNIX program used to transfer files from one UNIX site to another on a store and forward or polling basis, that is, a connection is only established when files need to be transferred and is not permanent. Most UUCP links are via modems and normal telephone lines usually at local call rates using one of the independent Packet Switching Service, such as Tymnet or IPSS. UUCP is slowly becoming redundant with most sites choosing to be permanently connect to a network. UUENCODE A common method of encoding 8-bit binary files, such as programs, into 7-bit ASCII files that can be included in e-mail messages and therefore transferred across e-mail systems that don't cater for the transmission of binary files. Such files, if stored without their e-mail counterpart normally have the file extender .UUE. A program, commonly called UUENCODE creates the UUENCODEd files and UUDECODE decodes the file back into its original 8-bit binary form. U 50 entries EOF