Megahertz Myth
Encyclopedia
The megahertz myth, or less commonly the gigahertz myth, refers to the misconception of only using clock rate
to compare the performance of different microprocessors. While clock rates are a valid way of comparing the performance of different speeds of the same model and type of processor, other factors such as pipeline depth and instruction set
s can greatly affect the performance when considering different processors. For example, one processor may take two clock cycles to add two numbers and another clock cycle to multiply by a third number, whereas another processor may do the same calculation in two clock cycles. Comparisons between different types of processors are difficult because performance varies depending on the type of task. A benchmark
is a more thorough way of measuring and comparing computer performance
.
based CPU architecture which Intel introduced in 1978 was used as the standard for the DOS
based IBM PC
, and developments of it still continue to dominate the Microsoft Windows
market. An IBM
RISC based architecture was used for the PowerPC
CPU which was released in 1992. In 1994 Apple Computer
introduced Macintosh computers using these PowerPC CPUs, but IBM's intention to produce its own desktop computers using these processors was thwarted by delays in Windows NT
and a falling out with Microsoft
. Initially this architecture met hopes for performance, and different ranges of PowerPC CPUs were developed, often delivering different performances at the same clock rate. Similarly, at this time the Intel 80486
was selling alongside the Pentium which delivered almost twice the performance of the 80486 at the same clock rate.
was commonly taken as a simple measure of processor performance, and was promoted in advertising and by enthusiasts without taking into account other factors. The term came into use in the context of comparing PowerPC
-based Apple Macintosh computers with Intel-based PCs. Marketing based on the myth led to the clock rate being given higher priority than actual performance, and led to AMD
introducing model numbers giving a notional clock rate based on comparative performance to overcome a perceived deficiency in their actual clock rate.
to surpass the PowerPC in performance. Apple then introduced Macs using the PowerPC 750 (or G3) which they claimed outperformed Pentium IIs while consuming less power. Intel continued to promote their higher clock rate, and the Mac press frequently used the "megahertz myth" term to emphasise claims that Macs had the advantage in certain real world uses, particularly in laptops.
Comparisons between PowerPC and Pentium had become a staple of Apple presentations. At the New York
Macworld Expo Keynote
on July 18, 2001, Steve Jobs
described an 867 MHz G4
as completing a task in 45 seconds while a 1.7 GHz Pentium 4 took 82 seconds for the same task, saying that "the name that we've given it is the megahertz myth". He then introduced senior hardware VP Jon Rubinstein
who gave a tutorial describing how shorter pipelines gave better performance at half the clock rate. The online cartoon Joy of Tech subsequently presented a series of cartoons inspired by Rubinstein's tutorial.
Clock rate
The clock rate typically refers to the frequency that a CPU is running at.For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wave...
to compare the performance of different microprocessors. While clock rates are a valid way of comparing the performance of different speeds of the same model and type of processor, other factors such as pipeline depth and instruction set
Instruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
s can greatly affect the performance when considering different processors. For example, one processor may take two clock cycles to add two numbers and another clock cycle to multiply by a third number, whereas another processor may do the same calculation in two clock cycles. Comparisons between different types of processors are difficult because performance varies depending on the type of task. A benchmark
Benchmark (computing)
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...
is a more thorough way of measuring and comparing computer performance
Computer performance
Computer performance is characterized by the amount of useful work accomplished by a computer system compared to the time and resources used.Depending on the context, good computer performance may involve one or more of the following:...
.
Background
The x86 CISCComplex instruction set computer
A complex instruction set computer , is a computer where single instructions can execute several low-level operations and/or are capable of multi-step operations or addressing modes within single instructions...
based CPU architecture which Intel introduced in 1978 was used as the standard for the DOS
DOS
DOS, short for "Disk Operating System", is an acronym for several closely related operating systems that dominated the IBM PC compatible market between 1981 and 1995, or until about 2000 if one includes the partially DOS-based Microsoft Windows versions 95, 98, and Millennium Edition.Related...
based IBM PC
IBM PC
The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...
, and developments of it still continue to dominate the Microsoft Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
market. An IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
RISC based architecture was used for the PowerPC
PowerPC
PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
CPU which was released in 1992. In 1994 Apple Computer
Apple Computer
Apple Inc. is an American multinational corporation that designs and markets consumer electronics, computer software, and personal computers. The company's best-known hardware products include the Macintosh line of computers, the iPod, the iPhone and the iPad...
introduced Macintosh computers using these PowerPC CPUs, but IBM's intention to produce its own desktop computers using these processors was thwarted by delays in Windows NT
Windows NT
Windows NT is a family of operating systems produced by Microsoft, the first version of which was released in July 1993. It was a powerful high-level-language-based, processor-independent, multiprocessing, multiuser operating system with features comparable to Unix. It was intended to complement...
and a falling out with Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
. Initially this architecture met hopes for performance, and different ranges of PowerPC CPUs were developed, often delivering different performances at the same clock rate. Similarly, at this time the Intel 80486
Intel 80486
The Intel 80486 microprocessor was a higher performance follow up on the Intel 80386. Introduced in 1989, it was the first tightly pipelined x86 design as well as the first x86 chip to use more than a million transistors, due to a large on-chip cache and an integrated floating point unit...
was selling alongside the Pentium which delivered almost twice the performance of the 80486 at the same clock rate.
Rise of the myth
The myth arose because the clock rateClock rate
The clock rate typically refers to the frequency that a CPU is running at.For example, a crystal oscillator frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate is that frequency reference translated by electronic circuitry into a corresponding square wave...
was commonly taken as a simple measure of processor performance, and was promoted in advertising and by enthusiasts without taking into account other factors. The term came into use in the context of comparing PowerPC
PowerPC
PowerPC is a RISC architecture created by the 1991 Apple–IBM–Motorola alliance, known as AIM...
-based Apple Macintosh computers with Intel-based PCs. Marketing based on the myth led to the clock rate being given higher priority than actual performance, and led to AMD
Advanced Micro Devices
Advanced Micro Devices, Inc. or AMD is an American multinational semiconductor company based in Sunnyvale, California, that develops computer processors and related technologies for commercial and consumer markets...
introducing model numbers giving a notional clock rate based on comparative performance to overcome a perceived deficiency in their actual clock rate.
Challenges to the myth
Computer advertising emphasized processor megahertz, and by late 1997 rapidly increasing clock rates enabled the Pentium IIPentium II
The Pentium II brand refers to Intel's sixth-generation microarchitecture and x86-compatible microprocessors introduced on May 7, 1997. Containing 7.5 million transistors, the Pentium II featured an improved version of the first P6-generation core of the Pentium Pro, which contained 5.5 million...
to surpass the PowerPC in performance. Apple then introduced Macs using the PowerPC 750 (or G3) which they claimed outperformed Pentium IIs while consuming less power. Intel continued to promote their higher clock rate, and the Mac press frequently used the "megahertz myth" term to emphasise claims that Macs had the advantage in certain real world uses, particularly in laptops.
Comparisons between PowerPC and Pentium had become a staple of Apple presentations. At the New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
Macworld Expo Keynote
Stevenote
"Stevenote" is a colloquial term for the keynote speeches given by former Apple CEO Steve Jobs at events such as the Worldwide Developers Conference and previously the Macworld and Apple Expos. Jobs' vibrant speaking style and manner of exciting the crowd was often referred to as inducing a...
on July 18, 2001, Steve Jobs
Steve Jobs
Steven Paul Jobs was an American businessman and inventor widely recognized as a charismatic pioneer of the personal computer revolution. He was co-founder, chairman, and chief executive officer of Apple Inc...
described an 867 MHz G4
PowerPC G4
PowerPC G4 is a designation used by Apple Computer to describe a fourth generation of 32-bit PowerPC microprocessors. Apple has applied this name to various processor models from Freescale, a former part of Motorola....
as completing a task in 45 seconds while a 1.7 GHz Pentium 4 took 82 seconds for the same task, saying that "the name that we've given it is the megahertz myth". He then introduced senior hardware VP Jon Rubinstein
Jon Rubinstein
Jonathan J. Rubinstein is an American computer scientist and electrical engineer who helped create the iPod, the portable music and video device first sold by Apple Computer Inc. in 2001...
who gave a tutorial describing how shorter pipelines gave better performance at half the clock rate. The online cartoon Joy of Tech subsequently presented a series of cartoons inspired by Rubinstein's tutorial.
External links
- Analysis: x86 Vs PPC — OSNews.com
- Apple's explanation of the megahertz myth Keynote at Macworld 2001
- Intel to 'ditch' Pentium 4 core after Prescott 2004 news article