The clock rate is the fundamental rate in cycles per second (measured in hertz) at which a computer performs its most basic operations such as adding two numbers or transferring a value from one processor register to another. Different chips on the motherboard may have different clock rates. Usually when referring to a computer, the term "clock rate" is used to refer to the speed of the CPU. This article is about the SI unit of frequency. ... This article is about the machine. ... 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. ... Integrated circuit of Atmel Diopsis 740 System on Chip showing memory blocks, logic and input/output pads around the periphery Microchips with a transparent window, showing the integrated circuit inside. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... CPU redirects here. ...

The clock rate of a CPU is normally determined by the frequency of an oscillator crystal. The first commercial PC, the Altair 8800 (by MITS), used an Intel 8080 CPU with a clock rate of 2 MHz (2 million cycles/second). The original IBM PC (c. 1981) had a clock rate of 4.77 MHz (4,770,000 cycles/second). In 1995, Intel's Pentium chip ran at 100 MHz (100 million cycles/second), and in 2002, an Intel Pentium 4 model was introduced as the first CPU with a clock rate of 3 GHz (three billion cycles/second). For other uses, see Frequency (disambiguation). ... Oscillation is the periodic variation, typically in time, of some measure as seen, for example, in a swinging pendulum. ... Altair 8800 Computer with 8 inch floppy disk system The MITS Altair 8800 was a microcomputer design from 1975, based on the Intel 8080 CPU. Sold as a kit through Popular Electronics magazine, the designers intended to sell only a few hundred to hobbyists, and were surprised when they sold... IBM PC (IBM 5150) with keyboard and green screen monochrome monitor (IBM 5151), running MS-DOS 5. ... Year 1981 (MCMLXXXI) was a common year starting on Thursday (link displays the 1981 Gregorian calendar). ... Year 1995 (MCMXCV) was a common year starting on Sunday (link will display full 1995 Gregorian calendar). ... 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. ... This article does not cite any references or sources. ... Also see: 2002 (number). ... 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. ...

Comparing

The clock rate of a computer is only useful for providing comparisons between computer chips in the same processor family. An IBM PC with an Intel 486 CPU running at 50 MHz will be about twice as fast as one with the same CPU, memory and display running at 25 MHz, while the same will not be true for MIPS R4000 running at the same clock rate as the two are different processors with different functionality. Furthermore, there are many other factors to consider when comparing the speeds of entire computers, like the clock rate of the computer's front side bus, the clock rate of the RAM, the width in bits of the CPU's bus and the amount of Level 1, Level 2 and Level 3 cache. Intel i486 DX2- top view The Intel i486 (also called 486 or 80486) is a range of Intel CISC microprocessors which is part of the Intel x86 family of processors. ... CPU redirects here. ... In personal computers, the front side bus (FSB) or system bus is the physical bi-directional bus that carries all electronic signal information between the central processing unit (CPU) and the northbridge. ... RAM redirects here. ... Diagram of a CPU memory cache A CPU cache is a cache used by the central processing unit of a computer to reduce the average time to access memory. ...

Clock rates should not be used when comparing different computers or different processor families. Rather, some software benchmark should be used. Clock rates can be very misleading since the amount of work different computer chips can do in one cycle varies. For example, RISC CPUs tend to have simpler instructions than CISC CPUs (but higher clock rates), and superscalar processors can execute more than one instruction per cycle, yet it is not uncommon for them to do "less" in a clock cycle. In addition, subscalar CPUs, or use parallelism, can also affect the quality of the computer regardless of clock rate. In computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it. ... Reduced Instruction Set Computer (RISC), is a microprocessor CPU design philosophy that favors a smaller and simpler set of instructions that all take about the same amount of time to execute. ... A Complex Instruction Set Computer (CISC) is an instruction set architecture (ISA) in which each instruction can indicate several low-level operations, such as a load from memory, an arithmetic operation, and a memory store, all in a single instruction. ... Simple superscalar pipeline. ...

History

In the early 1990s, most computer companies advertised their computers' speed chiefly by referring to their CPUs' clock rates. This led to various marketing games, such as Apple Computer's decision to create and market the Power Macintosh 8100/110 with a clock rate of 110 MHz so that Apple could advertise that its computer had the fastest clock speed available—the fastest Intel processor available at the time ran at 100 MHz. This superiority in clock speed, however, was meaningless since the PowerPC and Pentium CPU architectures were completely different. The Power Mac was faster at some tasks but slower at others. For the band, see 1990s (band). ... Apple Inc. ... PowerPC is a RISC microprocessor architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors as well. ... This article does not cite any references or sources. ...

After 2000, Intel's competitor, AMD, started using model numbers instead of clock rates to market its CPUs because of the lower CPU clocks when compared to Intel. Continuing this trend it attempted to dispel the "Megahertz myth" which it claimed did not tell the whole story of the power of its CPUs. In 2004, Intel announced it would do the same, probably because of consumer confusion over its Pentium M mobile CPU, which reportedly ran at about half the clock rate of the roughly equivalent Pentium 4 CPU. As of 2007, performance improvements have continued to come through innovations in pipelining, instruction sets, and the development of multi-core processors, rather than clock speed increases (which have been constrained by CPU power dissipation issues). However, the transistor count has continued to increase as predicted by Moore's Law. Year 2000 (MM) was a leap year starting on Saturday (link will display full 2000 Gregorian calendar). ... Advanced Micro Devices, Inc. ... This article or section is not written in the formal tone expected of an encyclopedia article. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Introduced in March 2003, the Pentium M is an x86 architecture microprocessor designed and manufactured by Intel. ... An instruction set is (a list of) all instructions, and all their variations, that a processor can execute. ... Diagram of an Intel Core 2 dual core processor, with CPU-local Level 1 caches, and a shared, on-die Level 2 cache. ... CPUs (Central processing units) in their various incarnations consume some amount of electric power. ... Transistor count is the most common measure of chip complexity. ... Gordon Moores original graph from 1965 Growth of transistor counts for Intel processors (dots) and Moores Law (upper line=18 months; lower line=24 months) For the observation regarding information retrieval, see Mooers Law. ...

See also

• Bit rate
• Clock recovery
• Clock signal
• Data transfer rate
• Instruction cycle
• Overclocking
• PR rating
• System time

In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... Some digital data streams, especially high-speed serial data streams (such as the raw stream of data from the magnetic head of a disk drive) are sent without an accompanying clock. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ... In telecommunications, data transfer rate or just transfer rate is the average number of bits, characters, or blocks per unit time passing between equipment in a data transmission system. ... The instruction cycle is the time period during which one instruction is fetched from memory and executed when a computer is given an instruction in machine language. ... AMD Athlon XP Overclocking BIOS Setup on ABIT NF7-S. FSB frequency (External clock) has increased from 133 MHz to 148 MHz, and clock multiplier factor has changed from 13. ... The PR rating system was developed by AMD in the mid-1990s as a method of comparing their x86 processors to those of rival Intel. ... In computer science and computer programming, system time represents a computer systems notion of the passing of time. ...

References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. This article does not cite any references or sources. ... “GFDL” redirects here. ...