1. One of a small number of high-speed memory locations in a computer's CPU. Registers differ from ordinary random access memory in several respects:

There are only a small number of registers (the "register set"), typically 32 in a modern processor though some, e.g. SPARC, have as many as 144. A register may be directly addressed with a few bits. In contrast, there are usually millions of words of main memory (RAM), requiring at least twenty bits to specify a memory location. Main memory locations are often specified indirectly, using an indirect addressing mode where the actual memory address is held in a register.

Registers are fast; typically, two registers can be read and a third written -- all in a single cycle. Memory is slower; a single access can require several cycles.

The limited size and high speed of the register set makes it one of the critical resources in most computer architectures. Register allocation, typically one phase of the back-end, controls the use of registers by a compiled program.

See also: accumulator, FUBAR, orthogonal, register dancing, register allocation, register spilling.

2. An addressable location in a memory-mapped peripheral device. E.g. the transmit data register in a UART.

(03 Feb 2009)

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1. A written account or entry; an official or formal enumeration, description, or record; a memorial record; a list or roll; a schedule. "As you have one eye upon my follies, . . . Turn another into the register of your own." (Shak)

2. A record containing a list and description of the merchant vessels belonging to a port or customs district. A certificate issued by the collector of customs of a port or district to the owner of a vessel, containing the description of a vessel, its name, ownership, and other material facts. It is kept on board the vessel, to be used as an evidence of nationality or as a muniment of title.

3. [Cf. LL. Registrarius. Cf. Regisrar] One who registers or records; a registrar; a recorder; especially, a public officer charged with the duty of recording certain transactions or events; as, a register of deeds.

4. That which registers or records. Specifically: The part of a telegraphic apparatus which records automatically the message received. A machine for registering automatically the number of persons passing through a gateway, fares taken, etc.; a telltale.

5. A lid, stopper, or sliding plate, in a furnace, stove, etc, for regulating the admission of air to the fuel; also, an arrangement containing dampers or shutters, as in the floor or wall of a room or passage, or in a chimney, for admitting or excluding heated air, or for regulating ventilation.

6. The inner part of the mold in which types are cast. The correspondence of pages, columns, or lines on the opposite or reverse sides of the sheet.

The correspondence or adjustment of the several impressions in a design which is printed in parts, as in chromolithographic printing, or in the manufacture of paper hangings. See Register.

7. The compass of a voice or instrument; a specified portion of the compass of a voice, or a series of vocal tones of a given compass; as, the upper, middle, or lower register; the soprano register; the tenor register.

In respect to the vocal tones, the thick register properly extends below from the F on the lower space of the treble staff. The thin register extends an octave above this. The small register is above the thin. The voice in the thick register is called the chest voice; in the thin, the head voice. Falsetto is a kind off voice, of a thin, shrull quality, made by using the mechanism of the upper thin register for tones below the proper limit on the scale.

A stop or set of pipes in an organ. Parish register, A book in which are recorded the births, baptisms, marriages, deaths, and burials in a parish.

Synonyms: List, catalogue, roll, record, archives, chronicle, annals. See List.

Origin: OE. Registre, F. Registre, LL. Registrum,regestum, L. Regesta, pl, fr. Regerere, regestum, to carry back, to register; pref. Re- re- + gerere to carry. See Jest, and cf. Regest.

(01 Mar 1998)