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Encyclopedia > Processor register

In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to frequently used values—typically, these values are involved in multiple expression evaluations occurring within a small region on the program. Most, but not all, modern computer architectures operate on the principle of moving data from main memory into registers, operating on them, then moving the result back into main memory—a so-called load-store architecture. A typical vision of a computer architecture as a series of abstraction layers: hardware, firmware, assembler, kernel, operating system and applications (see also Tanenbaum 79). ... This article does not cite any references or sources. ... A computer program is a collection of instructions that describe a task, or set of tasks, to be carried out by a computer. ... An expression in a programming language is a combination of values and functions or procedures, interpreted according to the particular rules of precedence and of association for a particular programming language, which computes and then returns another value. ... This article is about the computer architecture. ...


Processor registers are at the top of the memory hierarchy, and provide the fastest way for a cpu to access data. The term is often used to refer only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set. More properly, these are called the "architectural registers". For instance, the x86 instruction set defines a set of eight 32-bit registers, but a CPU that implements the x86 instruction set will contain many more registers than just these eight. The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. ... CPU can stand for: in computing: Central processing unit in journalism: Commonwealth Press Union in law enforcement: Crime prevention unit in software: Critical patch update, a type of software patch distributed by Oracle Corporation in Macleans College is often known as Ash Lim. ... It has been suggested that some sections of this article be split into a new article entitled instruction set architecture. ... x86 or 80x86 is the generic name of a microprocessor architecture first developed and manufactured by Intel. ... “CPU” redirects here. ...


Allocating frequently used variables to registers can be critical to a program's performance. This action, namely register allocation is performed by a compiler in the code generation phase. In compiler optimization, register allocation is the process of multiplexing a large number of target program variables onto a small number of CPU registers. ... A diagram of the operation of a typical multi-language, multi-target compiler. ... This article or section does not adequately cite its references or sources. ...


Categories of registers

Registers are normally measured by the number of bits they can hold, for example, an "8-bit register" or a "32-bit register". Registers are now usually implemented as a register file, but they have also been implemented using individual flip-flops, high speed core memory, thin film memory, and other ways in various machines. This article is about the unit of information. ... 8-bit refers to the number of bits used in the data bus of a computer. ... 32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ... A register file is an array of processor registers in a central processing unit (CPU). ... In digital circuits, the flip-flop, latch, or bistable multivibrator is an electronic circuit which has two stable states and thereby is capable of serving as one bit of memory. ... A 16×16 cm area core memory plane of 128×128 bits, i. ... Thin film memory is a high-speed variation of core memory developed by Sperry Rand in a government-funded research project. ...


There are several classes of registers according to the content:

  • Data registers are used to store integer numbers (see also Floating Point Registers, below). In some older and simple current CPUs, a special data register is the accumulator, used implicitly for many operations.
  • Address registers hold memory addresses and are used to access memory. In some CPUs, a special address register is an index register, although often these hold numbers used to modify addresses rather than holding addresses.
  • Conditional registers hold truth values often used to determine whether some instruction should or should not be executed.
  • General purpose registers (GPRs) can store both data and addresses, i.e., they are combined Data/Address registers.
  • Floating point registers (FPRs) store floating point numbers in many architectures.
  • Constant registers hold read-only values such as zero, one, or pi.
  • Vector registers hold data for vector processing done by SIMD instructions (Single Instruction, Multiple Data).
  • Special purpose registers hold program state; they usually include the program counter (aka instruction pointer), stack pointer, and status register (aka processor status word).
    • Instruction registers store the instruction currently being executed.
    • Index registers are used for modifying operand addresses during the run of a program.
  • In some architectures, model-specific registers (also called machine-specific registers) store data and settings related to the processor itself. Because their meanings are attached to the design of a specific processor, they cannot be expected to remain standard between processor generations.
  • Control and status registers - It has three types. Program counter, instruction registers, Program status word (PSW).
  • Registers related to fetching information from RAM, a collection of storage registers located on separate chips from the CPU (unlike most of the above, these are generally not architectural registers):

Hardware registers are similar, but occur outside CPUs. In computer science, the term integer is used to refer to any data type which can represent some subset of the mathematical integers. ... In a computer CPU, an accumulator is a register in which intermediate arithmetic and logic results are stored. ... The terms storage (U.K.) or memory (U.S.) refer to the parts of a digital computer that retain physical state (data) for some interval of time, possibly even after electrical power to the computer is turned off. ... An index register in a computer CPU is a processor register used for modifying operand addresses during the run of a program, typically for doing vector/array operations. ... In logic, a truth value, or truth-value, is a value indicating to what extent a statement is true. ... A floating-point number is a digital representation for a number in a certain subset of the rational numbers, and is often used to approximate an arbitrary real number on a computer. ... When a circles diameter is 1, its circumference is π. Pi or π is the ratio of a circles circumference to its diameter in Euclidean geometry, approximately 3. ... A vector processor, or array processor, is a CPU design that is able to run mathematical operations on multiple data elements simultaneously. ... -1... The program counter (also called the instruction pointer in some computers) is a register in a computer processor which indicates where the computer is in its instruction sequence. ... In computer science, a call stack is a special stack which stores information about the active subroutines of a computer program. ... A status register is a collection of flag bits for a microprocessor that indicates the status of various mathematical operations. ... In computing, an instruction register is the part of a CPUs control unit that stores the instruction currently being executed. ... In mathematics, an operand is one of the inputs (arguments) of an operator. ... Random access memory (usually known by its acronym, RAM) is a type of data storage used in computers. ... The Memory Buffer Register (MBR) in the central processor that stores the data being transferred to and from the immediate access store. ... The memory data register is the register of a computers control unit that contains the contents of a register to fetch or store from or to the computer storage. ... The memory address register is the register of a computers control unit that contains the address of a register to fetch or store from or to the computer storage. ... Memory Type Range Registers (MTRRs) are control registers that are used as a control mechanism which provides system software with control of how accesses to memory ranges by the CPU are cached. ... In computing, a hardware register is a storage area for hardware I/O (input/output) of different kinds. ...


Some examples

The table below shows the number of registers of several mainstream processors. Note that the stack pointer (ESP) is counted as an integer register on x86-compatible processors, even though there are a limited number of instructions that may be used to operate on its contents.

Processors Integer registers Double FP registers
Intel Core Duo 8 8
Intel Core 2 16 16
Pentium 4 8 8
Pentium 4 with EM64T 16 16
Athlon 64 16 16
Athlon MP 8 8
Opteron 240 16 16
Itanium 2 128 128
UltraSPARC IIIi 32 32
POWER3 32 32
6502 3 0

Intel Core Duo brand logo Intel Core Solo brand logo The Core brand refers to Intels 32-bit mobile dual-core x86 CPUs derived from the Pentium M branded processors microarchitecture (an interim step between the Intel P6 and Core microarchitecture), which emerged in parallel with the NetBurst... The Core 2 brand refers to a range of Intels consumer dual-core and quad-core (2x2) 64-bit x86 CPUs based on the Intel Core microarchitecture, which derived from the 32-bit dual-core Yonah laptop processor. ... The Pentium 4[1] brand refers to Intels mainstream desktop and mobile single-core CPUs (introduced on November 20, 2000[2]) with the seventh-generation NetBurst architecture, which was the companys first all-new design since the Intel P6 of the Pentium Pro branded CPUs of 1995. ... The Pentium 4[1] brand refers to Intels mainstream desktop and mobile single-core CPUs (introduced on November 20, 2000[2]) with the seventh-generation NetBurst architecture, which was the companys first all-new design since the Intel P6 of the Pentium Pro branded CPUs of 1995. ... The Athlon 64 is an eighth-generation, AMD64 architecture microprocessor produced by AMD, released on September 23, 2003. ... Athlon is the brand name applied to a series of different x86 processors designed and manufactured by AMD. The original Athlon, or Athlon Classic, was the first seventh-generation x86 processor and, in a first, retained the initial performance lead it had over Intels competing processors for a significant... The AMD Opteron was the AMDs x86 server processor line, and the first processors to implement the AMD64 (also known as x86-64) instruction set architecture. ... Itanium 2 logo The Itanium 2 is an IA-64 64-bit microprocessor developed jointly by Hewlett-Packard (HP) and Intel, and introduced on July 8, 2002. ... SPARC (Scalable Processor ARChitecture) is a RISC microprocessor architecture originally designed in 1985 by Sun Microsystems. ... Released in 1998: 15 million transistors per chip The first 64-bit symmetric multiprocessor (SMP), POWER3 is completely compatible with the original POWER instruction set -- and compatible with the PowerPC instruction set as well. ... The MOS Technology 6502 is an 8-bit microprocessor designed by MOS Technology in 1975. ...

See also

Computer science Portal

  Results from FactBites:
 
Processor register - Wikipedia, the free encyclopedia (495 words)
In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a given point in time.
Processor registers are the top of the memory hierarchy, and provide the fastest way for the system to access data.
Registers are now usually implemented as a register file, but they have also been implemented using individual flip-flops, high speed core memory, thin film memory, and other ways in various machines.
Itanium® Processor Family Performance Advantages: Register Stack Architecture - Intel® Software Network (1256 words)
And with only a small number of processor registers at its disposal, the compiler would soon run out of registers while the nesting level of function calls would be very shallow.
The register stack serves a similar function as the memory stack in traditional processors, but the register stack is managed internally by the processor.
Instructions that use processor registers exclusively don't have to wait for the memory cycles to complete; they perform all their work at full speed inside the processor.
  More results at FactBites »

 
 

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