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In computer architecture, Instructions Per Clock (Instruction Per Cycle or IPC) is a term used to describe one aspect of a processor's performance: the average number of instructions executed for each clock cycle. It is the multiplicative inverse of Cycles Per Instruction. Wikipedia does not have an article with this exact name. ... Cycles per instruction, also known as clock cycles per instruction, or clocks per instruction (CPI) is the number of clock cycles that happen when a instruction is being executed by a computer with a given clock frequency. ... 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). ... CPU redirects here. ... In computer science, an instruction typically refers to a single operation of a processor within a computer architecture. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ... The reciprocal function: y = 1/x. ... Cycles per instruction, also known as clock cycles per instruction, or clocks per instruction (CPI) is the number of clock cycles that happen when a instruction is being executed by a computer with a given clock frequency. ...

Explanation

Calculation of IPC

The number of instructions per second for a processor can be derived by multiplying the instructions per cycle and the clock speed (measured in cycles per second or Hz) of the processor in question. The number of instructions per second is an approximate indicator of the likely performance of the processor. Instructions per second (IPS) is a measure of a computers processor speed. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ... The hertz (symbol: Hz) is the SI unit of frequency. ...

The number of instructions executed per clock is not a constant for a given processor; it depends on how the particular software being run interacts with the processor, and indeed the entire machine, particularly the memory hierarchy. However, certain processor features tend to lead to designs that have higher-than-average IPC values; the presence of multiple ALU's (an ALU is a processor subsystem that can perform elementary arithmetic and logical operations), and short pipelines. When comparing different instruction sets, a simpler instruction set may lead to a higher IPC figure than an implementation of a more complex instruction set using the same chip technology; however, the more complex instruction set may be able to achieve more useful work with fewer instructions. Computer software (or simply software) refers to one or more computer programs and data held in the storage of a computer for some purpose. ... The hierarchical arrangement of storage in current computer architectures is called the memory hierarchy. ... ALU redirects here. ... An instruction set, or instruction set architecture (ISA), describes the aspects of a computer architecture visible to a programmer, including the native datatypes, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O (if any). ...

Factors governing IPC

A given level of instructions per second can be achieved with a high IPC and a low clock speed (like the AMD Athlon, Intel Core 2, HP PA-RISC, or Sun Microsystems SPARC), or from a low IPC and high clock speed (like the Intel Pentium 4 or DEC Alpha). Advanced Micro Devices, Inc. ... 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... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... Core 2 Duo brand logo This article is about Intel processors branded as Intel Core 2. ... The Hewlett-Packard Company (NYSE: HPQ), commonly known as HP, is a very large, global company headquartered in Palo Alto, California, United States. ... PA-RISC is a microprocessor architecture developed by Hewlett-Packards Systems & VLSI Technology Operation. ... Sun Microsystems, Inc. ... Sun UltraSPARC II Microprocessor Sun UltraSPARC T1 (Niagara 8 Core) SPARC (Scalable Processor ARChitecture) is a pure big-endian RISC microprocessor instruction set architecture originally designed in 1985 by Sun Microsystems. ... Intel Corporation (NASDAQ: INTC, SEHK: 4335), founded in 1968 as Integrated Electronics Corporation, is an American multinational corporation that is best known for designing and manufacturing microprocessors and specialized integrated circuits. ... New Intel Pentium 4 with Hyper Threading logo The Pentium 4 is a seventh-generation x86 architecture microprocessor produced by Intel and is their first all-new CPU design, called the NetBurst architecture, since the Pentium Pro of 1995. ... DEC Alpha AXP 21064 Microprocessor The DEC Alpha, also known as the Alpha AXP, is a 64-bit RISC microprocessor originally developed and fabricated by Digital Equipment Corp (DEC). ...

High-IPC, low-clock speed processor designs are traditionally called "brainiac" designs, while low-IPC, high-clock speed are often called "speed-demons". Both are valid processor designs, and the choice between the two is often dictated by history, engineering constraints, or marketing pressures. This article or section does not cite its references or sources. ... This article or section does not cite its references or sources. ...

Computer speed

The useful work that can be done with any computer depends on many factors besides the processor speed. These factors include the processor architecture, the internal layout of the machine, the speed of the disk storage system, the speed of other attached devices, the efficiency of the operating system, and most importantly the high level design of the application software in use. To a large extent, the design of a CPU, or central processing unit, is the design of its control unit. ... Disk storage is a group of data storage mechanisms for computers; data are transferred to planar surfaces or disks for temporary or permanent storage. ... An operating system (OS) is a computer program that manages the hardware and software resources of a computer. ... Application software is a defined subclass of computer software that employs the capabilities of a computer directly to a task that the user wishes to perform. ...

For users and purchasers of a computer system, Instructions Per Clock is not a particularly useful indication of the performance of their system. For an accurate measure of performance relevant to them, application benchmarks are much more useful. Awareness of its existence is useful, in that it provides an easy-to-grasp example of why clock speed is not the only factor relevant to computer performance. In computing, a benchmark is the result of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, by running a number of standard tests and trials against it. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ...

See also

• Cycles Per Instruction
• The benchmark article provides a useful introduction to computer performance measurement for those readers interested in the topic.