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| Glossary of Terms |  |
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| Address | A specified location, usually in the computer's memory, or on disc. | |
| Address bus | A specialised data channel used to pass addresses from one part of a microcomputer to another. | |
| Addressing | The convention or method of using addresses in a micro. This varies from machine to machine. | |
| ADFS | Advanced Disc Filing System. One of the two standard disc filing systems on Acorn micro-computers. ADFS is the later, and is used by the 512 when initially loading DOS. | |
| Architecture | Literally the hardware design concepts used in a computer. | |
| Assembler | A program which reads assembly code and translates it to machine readable instructions. Also used, colloquially, for the code itself. | |
| AUX | DOS abbreviation for auxiliary. In standard systems it refers to both the system's auxiliary input and output devices, AUXIN and AUXOUT. These are normally assigned to RS423 receive and transmit. See also Serial port. | |
| AUXIN | The logical serial input device, by default the RS423. | |
| AUXOUT | The logical serial output device, by default the RS423. | |
| Batch | A group of items which logically belong together. | |
| Batch-file | A DOS file used to hold a sequence of instructions which can be read by DOS in such a way as to run programs and perform a series of related tasks automatically. | |
| Batch-processing | A method of processing bulk information. | |
| Block | A group of bytes in memory or on disc which form a logically addressable unit. | |
| Bootstrap | Properly 'bootstrap loader'. A small, usually permanent (ie electronically encoded on a chip) program provided to load the operating software required by a computer. The term derives literally from the concept of the machine pulling itself up by its bootlaces. | |
| Bus | An electrical connection along which data of various types may be passed from one area in a micro to another. Literally a common communication path. | |
| C | A high level, compiled computer language. | |
| Character | Literally, any single byte of information. Colloquially often used to describe only displayable items of data, eg A, B, C, etc. | |
| Clock | Either the function which the user sees as providing the time of day, or the device within a computer which provides regular pulses to all other time dependent devices within the machine, so as to orchestrate and synchronise their actions. | |
| Cluster | An area of disc storage, allocated as the minimum sized 'extra' unit when a DOS file requires more space. The size of a cluster is 1 kilobyte, but, therefore, the number of sectors per cluster varies, depending on the disc format. | |
| CON | DOS abbreviation for console. In standard systems it refers to the default systems input and output devices, CONIN and CONOUT, the screen and keyboard. In use in commands it is suffixed by a colon. | |
| CONIN | The logical input device, by default the keyboard. | |
| CONOUT | The logical output device, by default the screen. | |
| CP/M | Control Program for Micros. The 'standard' operating system for 8-bit business machines prior to DOS systems, and the direct ancestor of DOS. | |
| CPU | Central Processing unit. In micros this is often a single chip, a microprocessor. In larger systems it is usually a logical unit which may contain many chips and may require several boards. | |
| Current directory | The directory presently known by the system to be used when reading or writing files, unless explicitly instructed to the contrary. However, see also 'Path'. | |
| Data bus | A specialised type of bus used to pass data from one unit in a micro to another which requires the information. | |
| Delimiter | Literally a separation character, used to distinguish between one logical part of an area of information and another. For DOS commands requiring parameters, each item is delimited by a space. | |
| Device | In DOS a device is any logical unit attached to the computer for input or output. | |
| DFS | Disc Filing System. One of the two standard disc filing systems on current Acorn microcomputers. DFS was the original system, but is not compatible with the later ADFS. | |
| Directory | A logical unit which must be named and created on disc, and which can hold filenames or other directories. See also 'Current directory'. | |
| DOS | Disc Operating System. The name of the type of operating system used by the 80nnn family of processors, so named because it is loaded from disc. There are three popular versions, all of which share a common base but exhibit sufficient differences to preclude complete software compatibility | |
| File | A logical group of information stored on disc. It is the smallest unit which can be accessed by name by the user or applications. | |
| File allocation table | A table of information used by the portion of DOS responsible for disc storage, to record where the first fragment of of each file is physically located on the disc, and which areas are free to be used for new data. The minimum fragment is a cluster, and each cluster contains a pointer to the next, so DOS can retrieve the data. If either the FAT or a Cluster are corrupted, data may be lost. | |
| Filename | Either the complete 11 characters by which DOS can identify data stored on disc, or more correctly the first eight of these characters. | |
| GEM | Graphics Environment Manager. A front-end to DOS providing a highly formalised interface between a user and the operating system. Theoretically easier to use, but not always convenient and always slower than direct command line entry. | |
| I/O | Input/Output. A term used to refer to any computer activity or device which is concerned with this type of process. | |
| Interface | The intermediate device or process between two communicating parts of a computer's hardware or software. | |
| Interrupt | A hardware triggered function based on the system clock interval, which permits servicing of various internal activities on a regular basis. Typically, for example, the keyboard is scanned every 10 milliseconds to check if a key has been pressed. | |
| Label | In 512 DOS Plus this is the name of a command used to add a title to a disc. The title so added is known as the volume label. | |
| Logical device | A notional peripheral connection known to DOS. Each is assigned, by default, to an actual physical device by means of a 'device translation' table. If a physical connection is altered, by merely changing the translation table contents, the logical to physical relationships can be altered without any change to DOS's view of the outside world. See also CON, AUX, and PRN. | |
| Mouse | A hardware device connected to the micro for input of relative movements (of the mouse) on a flat surface, mimicked by a pointer on the screen. With suitable software this pointer can be used to choose one from a range of options, or to 'draw' on screen. See also WIMP. | |
| MS-DOS | The version of DOS as produced by Microsoft. | |
| Offset | The name given to a variable which indicates a point, usually in memory, with reference to a fixed base address or start-point. In DOS each segment points to a 64k block of memory, but the data within a segment is located by its offset from the start address of the segment. | |
| Parameter | Information supplied as a variable to limit or control or direct a process. For example, in a file copy operation both the source and destination filenames are parameters. | |
| Parallel port | A physical connection between the computer and the outside world, capable of passing eight bits of data simultaneously. That is, all eight data bits are passed through in parallel. This is the most common connection for printers. | |
| Port | A physical or notional connection between the computer and external devices. See also Logical device. | |
| PRN | DOS abbreviation for Printer. PRN is the logical printer device as known to DOS, by default attached to the parallel port. | |
| Register | In microprocessors, a special data storage area capable of use for a specified range of tasks on a defined quantity of data. In the 80186 in the 512 the registers can hold two bytes, or 16 bits of data, hence the description, 16-bit processor. Internal memory addressing uses registers specifically assigned to the task of referencing the current segment and the offset. By manipulating these registers different parts of memory are addressed. | |
| Segment | The name given to each 64 kilobytes of memory in the 512. A segment is the maximum unit that can be addressed in 16-bits. See also Register. | |
| Serial port | A physical connection between the computer and the outside world, capable of passing only a single bit of information at a time. That is, data bits are passed through in serial procession. In DOS the logical devices AUXIN and AUXOUT are assigned to the serial port by default. This is the standard connection for communications. See also Logical device. | |
| Transient command | A system command function which exists only during the time it is active. All transients must be loaded from an external storage device when called. | |
| Utility | A program written to carry out a defined task, often not an end in itself, but as a necessary adjunct to maintaining and running a computer, eg COPY, DEL, PRINT. | |
| Vector | A pointer found at a fixed location, and known to reference the address of a defined function, usually in the operating system. By means of vectors programs can 'legally' connect to all the various functions provided in operating system software, and remain compatible through version changes. | |
| WIMP | Windows, Icons, Menus and Pointer. A graphical user interface aimed, largely, at avoiding the keyboard by use of a mouse, which directs a visible pointer on the screen. The pointer is used to select one of the items offered. | |
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