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. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. A computer is a Machine that manipulates data according to a list of instructions. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage More generally, it is the frequency of the clock in any synchronous circuit. Different chips on the motherboard may have different clock rates (see CPU multiplier, Memory divider). Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A motherboard is the central or primary Printed circuit board (PCB making up a complex electronic system such as a modern Computer or Laptop The clock multiplier (or CPU multiplier or bus/core ratio) is the ratio of the internal CPU Clock rate to the frequency of its external address/data bus A Memory divider is a ratio which is used to determine the operating clock Frequency of Computer memory in accordance with Front Side Bus frequency if Usually when referring to a computer, the term "clock rate" is used to refer to the speed of the CPU.
A single clock cycle (typically lasting around few nanoseconds in modern microprocessors) toggles between a logical zero and a logical one state. In Electronics and especially synchronous Digital circuits a clock signal is a signal used to coordinate the actions of two or more circuits A nanosecond ( ns) is one billionth of a second See also times of other orders of magnitude. A microprocessor incorporates most or all of the functions of a Central processing unit (CPU on a single Integrated Historically, the logical zero state of a clock cycle persists longer than a logical one state due to thermal and electrical specification constraints.
CPU manufacturers typically charge premium prices for CPU's that operate at higher clock rates. For a given CPU, the clock rates are determined at the end of the manufacturing process through actual testing of each CPU. CPU's that are tested as complying with a given set of standards may be labeled with a higher clock rate, e. g. , 1. 50 GHz, while those that fail the standards of the higher clock rate yet pass the standards of a lesser clock rate may be labeled with the lesser clock rate, e. g. , 1. 33 GHz, and sold at a relatively lower price. [1] [2] Those looking to overclock a CPU to its maximum would be well-advised to purchase the highest clock rate sold for that CPU, since it has been tested at the highest standards for that CPU. However when going for a good price to performance ratio when buying a CPU it often pays off to get a lower clocked version of a CPU which can be overclocked the furthest percentagewise compared to other CPU's from that same CPU family. This way the relative percental increase in clock rate will be highest and the price to performance ratio can be maximized.
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Limits to clock rate
The clock rate of a CPU is normally determined by the frequency of an oscillator crystal. Frequency is a measure of the number of occurrences of a repeating event per unit Time. Oscillation is the repetitive variation typically in Time, of some measure about a central value (often a point of Equilibrium) or between two or more different states 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 MITS Altair 8800 was a Microcomputer design from 1975 based on the Intel 8080 CPU and sold as a mail-order kit through advertisements in The original IBM PC (c. 1981) had a clock rate of 4. Year 1981 ( MCMLXXXI) was a Common year starting on Thursday (link displays the 1981 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 corresponding to ~3.3 10-10seconds per cycle). Year 1995 ( MCMXCV) was a Common year starting on Sunday. Events of 1995 The Pentium brand refers to Intel 's single-core x86 Microprocessor based on the P5 fifth-generation Microarchitecture. See also 2002 (disambiguation Year 2002 ( MMII) was a Common year starting on Tuesday of the Gregorian calendar. The Pentium 4 brand refers to Intel 's line of single- core mainstream desktop and Laptop Central processing units (CPUs introduced To help compare Orders of magnitude of different Times this page lists times between 10&minus10 seconds and 10&minus9 seconds (100 Picoseconds
With any particular CPU, replacing the crystal with another crystal that oscillates half as fast (underclocking) will make the CPU run at half the speed. Underclocking also known as downclocking is the practice of modifying a synchronous circuit's speed settings to run at a lower Clock speed than the manufacturer's It will also make the CPU produce roughly half as much waste heat.
Some people try to speed up a CPU by replacing the oscillator crystal with a faster crystal (overclocking). However, those people will soon hit one or another of these 2 limits on clock rate:
- After each clock pulse, the wires inside the CPU needs time to settle to its new state. If the next clock pulse comes in too soon, while the wires are still settling (before every wire has finished transitioning from 0 to 1, or from 1 to 0), the results will be incorrect. Chip manufacturers publish a "maximum clock rate" specification, and they test chips before selling them to make sure they meet that specification, even when executing the most complicated instructions with the data patterns that take the longest to settle (testing at the temperature and voltage that runs the slowest).
- The energy used to charge a wire during the 0 to 1 transition is wasted as heat when that line is discharged during a 1 to 0 transition. When executing complicated instructions that cause lots of transitions, higher clock rates produce more heat. If electricity is converted to heat faster than a particular computer cooling system can get rid of it -- then the transistors may get hot enough to be destroyed. Computer cooling is the process of removing heat from computer components
People continue to find new ways to design CPUs that settle a little quicker or use slightly less energy per transition, pushing back those limits, producing new CPUs that can run at slightly higher clock rates. People also continue to find new ways to design CPUs such that, although they may run at the same or a slower clock rate as older CPUs, get more done per cycle. (See also Moore's Law). Moore's law describes an important trend in the History of computer hardware.
Comparing
The clock rate of a computer is only useful for providing comparisons between computer chips in the same processor family. The megahertz myth, or less commonly the gigahertz myth, refers to the error of using Clock rate to compare the performance of different Microprocessors 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. The Intel 486, otherwise known as the 80486 i486 or just 486 was the first tightly pipelined X86 design 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 (FSB), 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. In Personal computers the Front Side Bus ( FSB) is the bus that carries data between the CPU and the northbridge.
Clock rates should not be used when comparing different computers or different processor families. Rather, some software benchmark should be used. This article is about the use of benchmarks in computing for other uses see Benchmark. 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. A complex instruction set computer ( CISC, pronounced like " sisk " is a Microprocessor Instruction set architecture (ISA in which A superscalar CPU architecture implements a form of parallelism called Instruction-level parallelism within a single processor In addition, subscalar CPUs or use of parallelism can also affect the quality of the computer regardless of clock rate.
History
In the early 1990s, most computer companies advertised their computers' speed chiefly by referring to their CPUs' clock rates. The 1990s collectively refers to the years between and including 1990 and 1999 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. Apple Inc, ( formerly Apple Computer Inc, is an American Multinational corporation with a focus on designing and manufacturing Consumer electronics This superiority in clock speed, however, was meaningless since the PowerPC and Pentium CPU architectures were completely different. PowerPC is a RISC Instruction set architecture created by the 1991 Apple – IBM – Motorola alliance known as AIM The Pentium brand refers to Intel 's single-core x86 Microprocessor based on the P5 fifth-generation Microarchitecture. The Power Mac was faster at some tasks but slower at others.
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. 2000 ( MM) was a Leap year that started on Saturday of the Common Era, in accordance with the Gregorian calendar. 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. The megahertz myth, or less commonly the gigahertz myth, refers to the error of using Clock rate to compare the performance of different Microprocessors 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. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Overview The Pentium M represented a new and radical departure for Intel as it was not a low-power version of the desktop-oriented Pentium 4, but instead a heavily modified 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). In Computing, a pipeline is a set of data processing elements connected in series so that the output of one element is the input of the next one An instruction set is a list of all the instructions and all their variations that a processor can execute A multi-core processor (or chip-level multiprocessor, CMP) combines two or more independent cores into a single package composed of a single Integrated CPU s ( Central processing units in their various incarnations consume some amount of Electric power.
However, the transistor count has continued to increase as predicted by Moore's Law. Transistor count is the most common measure of chip complexity Moore's law describes an important trend in the History of computer hardware. And with the recent discovery that graphene nanoribbons may be able to replace silicon as the semiconductor in processors at least one researcher predicts that clock speeds in the terahertz range may be possible. Graphene nanoribbons (also called nano-graphene ribbons often abbreviated GNRs are thin strips of Graphene or unrolled Single-walled carbon nanotubes. [1].
References
- ^ Bullis, Kevin (2008-2-25). "TR10: Graphene Transistors". Technology Review. Technology Review is a magazine published by Technology Review Inc a media company owned by the Massachusetts Institute of Technology. Cambridge: MIT Technology Review, Inc.
See also
In Computing, a Computer bus operating with double data rate transfers data on both the rising and falling edges of the Clock signal. Quad data rate (or quad pumping) is a communication signaling technique wherein data is transmitted at both the rising and falling edges of the clock signal much the same way A pulse wave or pulse train is a kind of Non-sinusoidal Waveform that is similar to a Square wave, but does not have the symmetricalDapyx Software network: MP3 Explorer | Ebook Manager | Zenithic