Moore's law is a rule of thumb in the computer industry about the growth of computing power over time. Attributed to Gordon E. Moore the co-founder of Intel, it states that the growth of computing power follows an empirical exponential law. Moore originally proposed a 12 month doubling and, later, a 24 month period.
This 'law' can be interpreted with varying degrees of rigour and frequently is. The least rigorous interpretation of Moore's law is that computing power per unit cost will continue to grow exponentially. In this form, "Moore's law" has a factual basis and has proven useful for planning purposes.
The most rigorous interpretation of Moore's law is that the total number of transistors on the cheapest CPU will grow exponentially at a constant rate and that this constant rate produces a doubling every 12 (or 18, or 24) months. This variant oversimplifies a complex history.
The key problem with the process of finding evidence to support a rigorous interpretation of Moore's law lies in the use of multiple fudge factors. These include the choice of CPUs to look at; low-end or high-end, Intel's or some others'; the choice of point in a CPU's lifecycle; when introduced, when mass produced or when their production has been optimized; the cost of the CPU; in constant dollars adjusted for inflation, from which source, applying what discounts; and uncertainties inherent in accounting for clocking differences.
Additionally, the choice of chart can make seeing whether the data actually fit the curve difficult for people who are not very familiar with exponential curves. Sometimes, the charts advanced as evidence actually disprove the interpretation of Moore's law which is claimed to be true.
In summary, evidence for a rigorous interpretation of Moore's law cannot be considered scientific when the process by which it is gathered and interpreted is not disclosed. The few scientific investigations of Moore's law have concluded that a rigorous interpretation of it is not possible.
Nonetheless, the law, interpreted generally, has held for far longer than most authorities at the time would have believed and many experts expect its growth predictions to hold for the next decade or more.
The complexity for minimum component costs has increased at a rate of roughly a factor of two per year ... Certainly over the short term this rate can be expected to continue, if not to increase. Over the longer term, the rate of increase is a bit more uncertain, although there is no reason to believe it will not remain nearly constant for at least 10 years. That means by 1975, the number of components per integrated circuit for minimum cost will be 65,000. I believe that such a large circuit can be built on a single wafer.
Under the assumption that chip "complexity" is proportional to the number of transistors, regardless of what they do, the law has notably not held up to the test of time. In 1975,
"Moore's 1965 prediction that in 1975 the most cost efficient chips would incorporate 65,000 components was, in fact, wrong. The chip that Moore used in his 1975 presentation to show that his earlier prediction had been accurate, was a charge-coupled memory device that was just about to be introduced and it didn't have 64,000 components. Such a chip, therefore, strictly speaking did not exist. Furthermore it probably did not represent the most cost efficient chip, as it was quickly withdrawn from production. Indeed, the cost structure of different chip types had already become differentiated. In 1975 Intel introduced its first general purpose 8080 processor that started the PC revolution. It had 4,500 transistors.
— (The Lives and Death of Moore's Law)
Gordon Moore's observation was not named a "law" by Moore himself; that honor goes to Caltech professor, VLSI pioneer, and entrepreneur Carver Mead.
In 1975, Moore projected a doubling only every two years. He is adamant that he himself never said "every 18 months", but that is how it has been quoted. The SEMATECH roadmap follows a 24 month cycle.
In April 2005 Intel paid $10,000 to purchase a copy of the Electronics Magazine issue containing the original article.
Formulations of Moore's law
The most popular formulation is of the doubling of the number of transistors on integrated circuits (a rough measure of computer processing power) every 18 months. At the end of the 1970s, Moore's Law became known as the limit for the number of transistors on the most complex chips. However, it is also common to cite Moore's law to refer to the rapidly continuing advance in computing power per unit cost.
While growth has been continuous, no conceivable 'constant growth' law has held for hard disk storage cost per unit of information. The rate of growth in disk storage has been very uneven over the past decades and has markedly sped up more than once, corresponding to the utilization of error correcting codes, the magnetoresistive effect and the giant magnetoresistive effect. The current rate of increase in hard drive capacity is much faster than the rate of increase in transistor count and has been dubbed Kryder's law.
Another version claims that RAM storage capacity increases at the same rate as processing power. However, memory speeds have not increased as fast as CPU speeds in recent years, leading to a heavy reliance on caching in current computer systems.
An industry driver
Although Moore's law was initially made in the form of an observation and prediction, the more widely it became accepted, the more it served as a goal for an entire industry. This drove both marketing and engineering departments of semiconductor manufacturers to focus enormous energy aiming for the specified increase in processing power that it was presumed one or more of their competitors would soon actually attain. In this regard it can be viewed as a self-fulfilling prophecy.
The implications of Moore's law for computer component suppliers is very significant. A typical major design project (such as an all-new CPU or hard drive) takes between two and five years to reach production-ready status. In consequence, component manufacturers face enormous timescale pressures—just a few weeks' delay in a major project can spell the difference between great success and massive losses, even bankruptcy.
Expressed as "a doubling every 18 months", Moore's law suggests the phenomenal progress of technology in recent years. Expressed on a shorter timescale, however, Moore's law equates to an average performance improvement in the industry as a whole of over 1% a week. For a manufacturer competing in the cut-throat CPU market, a new product that is expected to take three years to develop and is just two or three months late is 10 to 15% slower, bulkier, or lower in storage capacity than the directly competing products, and is usually unsellable.
As of Q4 2004, current PC processors are fabricated at the 130 nm and 90 nm levels, with 65 nm chips being announced by the end of 2005. A decade ago, chips were built at a 500 nm level. Companies are working on using nanotechnology to solve the complex engineering problems involved in producing chips at the 45 nm, 30 nm, and even smaller levels—a process that will postpone the industry meeting the limits of Moore's Law.
Recent computer industry technology "roadmaps" predict (as of 2001) that Moore's Law will continue for several chip generations. Depending on the doubling time used in the calculations, this could mean up to 100 fold increase in transistor counts on a chip in a decade. The semiconductor industry technology roadmap uses a three-year doubling time for microprocessors, leading to about nine-fold increase in a decade.
Since the rapid exponential improvement could (in theory) put 100 GHz personal computers in every home and 20 GHz devices in every pocket, some commentators have speculated that sooner or later computers will meet or exceed any conceivable need for computation. This is only true for some problems—there are others where exponential increases in processing power are matched or exceeded by exponential increases in complexity as the problem size increases. See computational complexity theory and complexity classes P and NP for a (somewhat theoretical) discussion of such problems, which occur very commonly in applications such as scheduling.
Extrapolation partly based on Moore's Law has led futurologists such as Vernor Vinge, Bruce Sterling and Ray Kurzweil to speculate about a technological singularity. However, on April 13, 2005, Gordon Moore himself stated in an interview that the law may not hold valid for too long, since transistors may reach the limits of miniaturization at atomic levels.
In terms of size [of transistor] you can see that we're approaching the size of atoms which is a fundamental barrier, but it'll be two or three generations before we get that far—but that's as far out as we've ever been able to see. We have another 10 to 20 years before we reach a fundamental limit. By then they'll be able to make bigger chips and have transistor budgets in the billions.
Kurzweil replies that although around the year 2019, if Moore's Law keeps up, transistor features will be just a few atoms in width, and the strategy of ever finer photolithography will have run its course, this does not mean the end of Moore's Law. He notes that:
Moore's Law of Integrated Circuits was not the first, but the fifth paradigm to provide accelerating price-performance. Computing devices have been consistently multiplying in power (per unit of time) from the mechanical calculating devices used in the 1890 U.S. Census, to Turing's relay-based "Robinson" machine that cracked the Nazi enigma code, to the CBS vacuum tube computer that predicted the election of Eisenhower, to the transistor-based machines used in the first space launches, to the integrated-circuit-based personal computers.
Thus Kurzweil concludes that it is likely that some new type of technology will replace current integrated-circuit technology, and Moore's Law will hold true long after 2020. Kurzweil extends his analysis to include technologies from far before the integrated circuit to future forms of computation. He believes that the exponential growth of Moore's Law will continue beyond the use of integrated circuits into technologies that will lead to the technological singularity. The Law of Accelerating Returns described by Ray Kurzweil has in many ways altered the public's perception of Moore's law. It is a common (but mistaken) belief that Moore's Law makes predictions regarding all forms of technology, when really it only concerns semiconductor circuits. Many futurists still use the term "Moore's Law" to describe ideas like those put forth by Kurzweil.
Krauss and Starkman announced an ultimate limit of around 600 years in their paper "Universal Limits of Computation", based on rigorous estimation of total information-processing capacity of any system in the Universe.
Then again, the law has often met obstacles that appeared insurmountable, before soon surmounting them. In that sense, Mr. Moore says, he now sees his law as more beautiful than he had realised. "Moore's Law is a violation of Murphy's Law. Everything gets better and better." 
Not all aspects of computing technology develop in capacities and speed according to Moore's Law. Random Access Memory (RAM) speeds and hard drive seek times improve at best a few percentages per year.
Another, sometimes misunderstood, point is that exponentially improved hardware does not necessarily imply exponentially improved software to go with it. The productivity of software developers most assuredly does not increase exponentially with the improvement in hardware, but by most measures has increased only slowly and fitfully over the decades. Software tends to get larger and more complicated over time, and Wirth's law even states that "Software gets slower faster than hardware gets faster".
Moreover there is popular misconception that the clock speed of a processor determines its speed. This actually also depends on the number of instructions per tick which can be executed (as well as the complexity of each instruction, see MIPS, RISC and CISC), and as such the clock speed can only be used for comparison between two identical circuits. Of course, other factors are to be taken into consideration such as the bus size and speed of the peripherals. As such, most popular evaluations of "computer speed" are generally biased without an understanding of the underlying technology. This is especially true now that popular manufacturers play with public perception of speed, focusing on advertising the clock rate of new products.
It is interesting to note that as the cost of computer power continues to fall (from the perspective of a consumer), the cost for producers to achieve Moore's Law has followed the opposite trend: R&D, manufacturing, and test costs have increased steadily with each new generation of chips. As the cost of semiconductor equipment is expected to continue increasing, manufacturers must sell larger and larger quantities of chips to remain profitable. (The cost to "tapeout" a chip at 0.18u was roughly $300,000 USD. The cost to "tapeout" a chip at 90nm exceeds $750,000 USD, and the cost is expected to exceed $1.0M USD for 65nm.) In recent years, analysts have observed a decline in the number of "design starts" at advanced process nodes (0.13u and below.) While these observations were made in the period after the year 2000 economic downturn, the decline may be evidence that traditional manufacturers in the long-term global market cannot economically sustain Moore's Law.
- ^ Not to be confused with another G.E. Moore, the philosopher George Edward Moore, the creator of Moore's paradox.
- Exponential growth
- History of computing hardware (1960s-present)
- Observations named after people
- Rock's Law
- Intel's information page on Moore's Law – With link to Moore's original 1965 paper
- Intel press kit released for Moore's Law's 40th anniversary, with a 1965 sketch by Moore
- The Lives and Death of Moore's Law – By Ilkka Tuomi; a detailed study on Moore's law and its historical evolution
- Moore's Law Special at AMDboard – All the pertinent links to Moore's law material
- Moore says nanoelectronics face tough challenges – By Michael Kanellos, CNET News.com, 9 March, 2005
- It's Moore's Law, But Another Had The Idea First by John Markoff
- Happy birthday: The tale of a frivolous rule of thumb, The Economist, March 23, 2005
- Law that has driven digital life: The Impact of Moore's Law – A comprehensive BBC News article, 18 April, 2005
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