GLOSSARY

Absolute address A specific address (identification number) permanently assigned to a storage location, a device or a register by the designer.

Address A unique identification number of some source or destination data or an instruction.

Addressing mode The manner in which the processor determines the operand addresses within an instruction.

Address space The number of locations in the memory which can be located by the addressing technique used by the processor.

Architecture The organizational structure of a processor or the computer system.

Arithmetic and logic unit (ALU) A digital circuit which performs arithmetic and logic operations on operands.

Assembler A program that translates assembly language program into a machine language program.

Auto-increment addressing mode The content of a register is used as memory address and then automatically incremented by 1, 2, 4 or 8: useful for an array access or string processing.

Barrel shifter A special type of shifting circuit which shifts the input operand by an amount determined by a second input, in one clock period: used to implement complex addressing modes.

Branch or jump An instruction which makes the program control take a path different from the normal linear path.

Bus cycle The period of time in which a device connected to a bus completes all necessary operations for a single-bus transfer.

Cache’ memory A very high-speed, small, expensive, storage unit, which stores information (data or instruction) and which may be needed by the processor in near future.

Clock cycle A time period of the basic synchronizing mechanism within a processor.

Co-processor A specialized processor which executes specific functions independent of the main processor. Its presence in the system is expected to speed up computation.

Cycle stealing A technique used usually by direct memory access (DMA) for transferring data with the main memory, during which time the processor is prevented from using the memory busses.

Direct address An address that specifies the memory location of an operand in an instruction.

Effective address The final address of an operand or instruction, generated during an instruction execution, which goes to the memory system for the operand access.

Exception processing The processor state associated with interrupts, traps, tracing and other exceptional conditions.

Immediate address An address that is used as an operand value by an instruction.

Implied address An address not specified, but known implicitly by nature or op-code of an instruction.

Indexed address The effective address is generated by adding the content of a specified index register to the address contained within the instruction (usually known as a displacement).

Indirect address An address of a location where the address of an operand is stored.

Instruction set Specifies a processor's capability by listing all the instructions and details of its behaviour.

Linker Connects together programs which are compiled or assembled separately.

Loops A program control construct where a sequence of instructions is executed repeatedly till a specified termination condition is reached.

Machine language The language expressed in binary number system which a processor is able to follow without further translation.

Memory cycle time The minimum time which must elapse between two successive memory accesses.

Multitasking A property and technique of an operating system which allows more than one task to execute on a single processor concurrently.

Nested functions Definition of a function is embedded completely within the scope of another function, which is called lexical or static nesting. A function may call another function, and then it is called dynamic nesting.

Operand A datum or information item involved in the operation of an instruction and using which a result is computed.

Operating system A basic collection of programs which forms a layer of functionality above the bare hardware and provides resource (Processor, Memory, I/O devices, secondary storage) management and a virtual extended machine with more user-friendly interface.

Pipeline A technique by which a processor is able to initiate execution of more than one instruction at a time.

Pointer A storage location or a processor register which contains the address of some operand.

Register indirect address A register contains the address of an operand.

Relative address An address relative to a specified starting point.

Routine A group of instructions carrying out a specific activity.

Tracing A dynamic diagnostic technique in which a recording of the internal state of a processor permits later analysis of a program execution.

Virtual memory A hardware- and software-based memory management technique which permits the allocation of memory to individual programs much in excess of the physical main memory.