"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 ***************************************************************************** O Obey To perform the operations of an instruction. Object An entity. Also, the screen graphic shapes in a WIMP/GUI system, such as icons, menus, boxes. Object code Also machine code. The final result of a language translation. Object library A library of object code modules that can be called or included in programs at compilation and link time. Object oriented graphic See Vector graphic, Drawing program, GEM metafile. Object orientated programming - OOP A method of programming where the emphasis is on objects, such as data structures, and the operations performed upon them as opposed to control orientated programming where emphasis is on working out the program's flow of control. OOP is well suited to writing GUI programs where dialog boxes and sets of icons together with the routines connected with them can be treated as objects in the program. As modular or structured programming was the trend of the 1980s, OOPs is the fashion of the 1990s. The C++ language offers facilities to assist OOP although it is not a fully-fledged OOP language, such as Smalltalk. OCR Optical Character Recognition. Computer input equipment and techniques for identifying printed or handwritten characters by photoelectric sensing and analysis of their patterns. Octal A numeration system with a radix or base of eight using digits 0-7. The first five digit positions have the weights 1, 8, 64, 512, 4,096. In octal, decimal 10 would be 12. ODA Open Documents Architecture. A standard defined by the ISO and CCITT which allows documents containing graphics, text, spreadsheet data etc. to be passed between computers of different makes. Odd parity See Parity. OEM Original Equipment Manufacturer. A term applied by a supplier or distributor for a manufacturer who provides the components used in their product. Most (if not all) machines consist of components made by various OEMs and put together by the supplier whose name appears on the device. No components in an Atari computer are actually manufactured by Atari. Off-bit A term applied to a 0-bit as an indicator or flag. Off-hook The status of telephone equipment in which dialling is performed and messages are transmitted and received. Off-line Peripheral devices that are not under the control of a computer by being switched off or by the communications link being broken. Also, the state of not being connected to a remote data network. Off-line reader A program into which packets of messages and mail are loaded which enables the user to read them and reply to them as if on-line to a telecommunications network. The off-line reader will also prepare a message packet to up-load to the network containing the user's replies and messages. Off-line readers save enormous amounts of time on-line and thus expense. Off-line storage Any storage medium that has to be loaded or connected to the computer when required, such as a tape backup device. Offset A displacement, a difference between a location and a reference location, for instance, a relative address is an 'offset' of a base address. Also, to compensate or balance. Offspring Synonymous with member. OK button Common WIMP/GUI alert or dialog box button confirming the action to be taken and usually the default. According to Atari, "OK" should be in upper case and the button to the left of the "Cancel" button. OLR Off-Line Reader. OMR Optical Mark Recognition. Computer input equipment for identifying and interpreting marks (short lines, filled-in squares) on documents by means of changes in reflected or transmitted light. Commonly used on multiple choice exam papers and on National Lottery cards. On-bit A term applied to a 1-bit as an indicator or flag. On-board On the same printed circuit board as other components. On-chip On the same integrated circuit as other elements, such as the on-chip RAM cache of a MC68030 CPU. On-demand When required or requested. On-hook The status of telephone equipment in which it is ready to receive an incoming call. On-line The state of peripheral equipment connected and ready to perform its function being accessible to a computer. Also, having a terminal or computer connected to a remote interactive data processing service, data network or information system and receiving data from them. On-line storage Storage directly accessible to a computer at any time, such as RAM and disk drives. One-bit A 1-bit, a binary digit and the basic unit of storage and transmission. One-way communications Communication in one prearranged direction only, a simplex system. OOP Object Orientated Programming. Opcode OPeration CODE. That part of an object code instruction that consists of the operator. Also, an instruction set. Open An operating system function that locates and identifies a file in storage and its access permission. Also, to stop the flow of electricity in a circuit. Open circuit An electrical circuit where the current has been removed. Operand A value that is used or manipulated during the execution of an instruction, the basic unit of data. In the expression x + 3, both x and 3 are operands. Operating system - OS A set of tested, interrelated programs to exercise management and control functions over processing. It provides storage and processing management, protection of code and data including its validation, backup and error control, a human interface and in multi-user systems logging and accounting functions. The standard microcomputer operating system is MS-DOS and that in the ST-Falcon range is TOS with the addition of MultiTOS. Operating system header block All versions of TOS have a set of data at the start of the code which provides various information as to its identity and other miscellaneous details. The system variable _sysbase at address $4F2 points to the location of this header block and must be used by programmers, who should not assume that the system header block is in the ROM or at addresses $00FC0000 or $00E00000. The structure of the header block is: typedef struct _osheader { unsigned short os_entry; /* offset $00 */ unsigned short os_version; /* offset $02 */ void (*reseth)(void); /* offset $04 */ struct _osheader *os_beg; /* offset $08 */ void *os_end; /* offset $0C */ void *os_rsv1; /* offset $10 */ long *os_magic; /* offset $14 */ long os_date; /* offset $18 */ unsigned short os_conf; /* offset $1C */ unsigned short os_dosdate; /* offset $1E */ /* The following fields are not available in TOS 1.0 */ void **p_root; /* offset $20 */ unsigned char *pkbshift; /* offset $24 */ BASEPAGE **p_run; /* offset $28 */ void *p_rsv2; /* offset $2C */ } OSHEADER; Table O1: Interpretation of Operating System Header Block Offset from Meaning TOS 1.4 value _sysbase $00 Entry, BRA to reset handler $ 602E $02 Major TOS version number $ 01 $03 Minor TOS version number $ 04 $04 Address of routine executed upon reset $00FC0030 $08 Start of operating system $00FC0000 $0C Start of free RAM (end of system RAM) $0000611C $10 Address of default shell $00FC0030 $14 Address of GEM MUPB $00FE81FE $18 ROM creation date in hex $MMDDYYYY $04061989 $1C OS configuration bits $ 0007 $1E ROM creation date in GEMDOS format $ 1286 The following fields are not available in TOS 1.0 $20 Pointer to _root system variable $0000378C $24 Pointer to kbshift system variable $00000E7D $28 Pointer to _run system variable $00005622 $2C unused, reserved $00000000 The OS configuration bits field consists of the country code and video sync mode that the TOS was compiled for. Bit zero is 0 to indicate NTSC mode or 1 to indicate PAL mode. The remaining bits give the country code after being shifted right by one bit. Thus the above value of $07 gives %111 binary which is %1 for PAL mode and %11 or three for Great Britain (see Country). The three system variables are only available in TOS 1.2 and later. _root contains the address of the GEMDOS memory pool structure. kbshift contains the address of the system keyboard shift state variable which provides a quicker way of reading the state of the keyboard shift state than using the Kbshift() function. The _run variable contains the address of the basepage of the currently executing GEMDOS process. Operating system nucleus See Kernel. Operation During execution, that which is performed on or with data. Operator That part of an instruction or expression that specifies the operation to be performed on or with the operand(s), such as 'add', 'less-than' or 'NOT'. It can also be the symbol indicating that operation, such as +, < or NOT. Also, a person who performs processing related tasks in a mainframe/minicomputer computer installation. Optical A term denoting sensing and input by photoelectrical means. Optical character reader A device that carries out optical character recognition. Optical coupler Also optocoupler and opto-isolator. A sealed device containing an infra-red- emitting photodiode and a phototransistor sitting in a circuit and electrically isolating the circuit on either side of the component and so preventing noise and peak pulses from passing to the output side. The ST- Falcon range has these fitted to the MIDI lines for safety preventing excessive current from passing into the computer. Optical disk A storage device using laser beams to write (sometimes once only) and read data from a disk. The data is more secure than magnetizable disks and optical disks have far greater capacity. Optical mark reader A device that carries out optical mark recognition. Optical type font A special set of characters designed for machine reading. Optimization Also, tuning. The enhancement of a system or program to improve its speed of operation and/or storage space. This is often a process in programming where such methods can be done manually on the source code or by certain optimizer programs on the object code. Options menu A typical GEM application menu which contains such items as "Document defaults..." and "Preferences...". Optofile Atari name for the abortive CDAR504 CD-ROM drive. OR A logic operation with an output that is 'true' if any input is true and 'false' if all inputs are false. Order The operation of manipulating the physical relationship of items in a group according to some rule. Also, a command. Also, a term used to indicate that a value is an approximation, as in "in the order of 10%". Order code An instruction set. Origin A base address. Also, a root of a tree data structure. Originate To initiate or to be the source of. Originate mode A mode of telephone equipment (such as a modem) in which it is dialling a data station in order to set up a transfer. Orthogonal Having the characteristics of a matrix with items that are accessible at the intersections of two or three coordinates. OS Operating System. Oscillate To vibrate, to make a repetitive change of state or value. Oscillator A device that generates high-frequency pulses for purposes of synchronization and event timing. Most are crystal oscillators that take advantage of the inherent resonance of a quartz crystal to obtain frequency stability. The ST's 32 MHz oscillator provides the master clock frequency for the whole computer which is cut down to lower frequencies by the MMU, SHIFTER and GLUE chips for use by them and other integrated circuits including the CPU. OSI Open Systems Interconnect. An ISO international standard of protocols to eventually replace the Internet TCP/IP protocols. See TCP/IP. OTPEPROM One Time Programmable Erasable Read-Only Memory. An EPROM which can only be programmed once as the data on it cannot be erased. Outline The effect of drawing a line around a WIMP/GUI object for emphasis. Also, the main structure of an article, book, report etc. consisting of titles, headings and notes. Outline font See Scalable font. Outliner A text editor program helping to produce outlines of textual material to be written in a word processor. Outliners usually allow text to be 'folded', that is, some parts to be hidden so that the overall structure is more easily seen. Output To produce as a result of processing. That which is produced by a process or device. Also, a transfer to a peripheral device. Output buffer In a communications interface, the storage used to hold data that is awaiting transfer from a computer or modem. Output device A device used to convert data from its bit-pattern representation in storage to a form which can be used outside the computer system, such as a printer. Output medium The medium on which output data is represented, such as paper. Output routine A program routine or utility that organizes or performs an output. Outspacing The placing of extra space between characters in a DTP or document processor program for aesthetic effect. Overflow That part of a unit of data that will not fit into a storage location intended to receive it. Overhead In processing, the time or operations that are devoted to system functions rather than the job in hand. Overlay program A program that has been divided into overlay segments and a control segment usually because of memory limitations of the computer, common under MS-DOS on IBM PC compatibles. Overlay segment A part of an overlay program that is intended to be loaded when it is required during the execution of the program and overwritten when no longer required. Overload To exceed the designed work capacity of a system or functional unit or the safe current carrying capacity of an electric circuit. Overwrite To write new data to a storage location already occupied with data thus destroying it. Overwrite mode A program mode enabling the writing of characters over others and thus replacing them, rather than writing in-between them as in Insert mode. Owner In a hierarchical structure, an entity that has some degree of control or privilege with respect to entities (members) on a lower level. In a net data structure, an entity that must be accessed first in order to access other entities, such as the root directory of a drive before accessing a file in a subdirectory. O 78 entries EOF