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Prague Astronomical Clock

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The clock tower
The Prague Astronomical Clock or Prague Orloj (Czech: Pra?sky orloj, [pra?ski: ?rl?i]) is a medieval astronomical clock located in Prague, the capital of the Czech Republic, at 505?13.23?N 1425?15.30?E? / ?50.0870083 14.4209167? / 50.0870083; 14.4209167. The Orloj is mounted on the southern wall of Old Town City Hall in the Old Town Square and is a popular tourist attraction.
The Orloj is composed of three main components: the astronomical dial, representing the position of the Sun and Moon in the sky and displaying various astronomical details; "The Walk of the Apostles", a clockwork hourly show of figures of the Apostles and other moving sculptures; and a calendar dial with medallions representing the months.
Contents
1 History
2 Astronomical dial
2.1 Stationary background
2.2 Zodiacal ring
2.3 Old Czech time scale
2.4 Sun
2.5 Moon
2.6 Computer Model of Prague Orloj
3 Animated figures
4 Calendar
5 References
6 External Links
7 See also
//
History

Clock, calendar, and animated figures
The oldest part of the Orloj, the mechanical clock and astronomical dial, dates back to 1410 when it was made by clockmaker Mikul? of Kada? and Jan ?indel, the latter a professor.
Later, presumably around 1490, the calendar dial was added and clock facade decorated with gothic sculptures.
In 1552 it was repaired by Jan Taborsky, clock-master of Orloj, who also wrote a report on the clock where he mentioned Hanu? as maker of the clock. This was a mistake, and was corrected during the 20th century.
The Orloj stopped working many times in the centuries after 1552, and was repaired many times. Some speculate that the government purposely gouged out the original maker's eyes in order to prevent him from making a similar clock for another country. After this he died touching the clock, at which point the clock stopped working and remained unrepairable for a number of years. In the 17th century moving statues were added, and figures of the Apostles were added after major repair in 1865-1866.
The Orloj suffered heavy damage on May 7 and especially May 8, 1945, during the Prague Uprising, when Germans directed incendiary fire from several armored vehicles and an anti-aircraft gun to the south-west side of the Old Town Square in an effort to silence the provocative broadcasting initiated by the National Committee on May 5. The hall and nearby buildings burned along with the wooden sculptures on the Orloj and the calendar dial face made by Josef Mes. The machinery was repaired, the wooden Apostles restored by Vojt?ch Sucharda, and the Orloj started working again in 1948, but only after significant effort .
There exists a good deal of misinformation relating to the construction of the Orloj[citation needed]. For a long time it was believed that the Orloj was constructed in 1490 by clockmaster Jan R??e (also called Hanu?) and his assistant Jakub ?ech. Another fictitious story involves the clockmaker Hanu? being blinded on the order of the Prague Councillors.
Astronomical dial

Functions noted
The astronomical dial is a form of mechanical astrolabe, a device used in medieval astronomy. Alternatively, one may consider the Orloj to be a primitive planetarium, displaying the current state of the universe.
The astronomical dial has a background that represents the standing Earth and sky, and surrounding it operate four main moving components: the zodiacal ring, an outer rotating ring, an icon representing the Sun, and an icon representing the Moon.
Stationary background
The background represents the Earth and the local view of the sky. The blue circle directly in the center represents the Earth, and the upper blue is the portion of the sky which is above the horizon. The red and black areas indicate portions of the sky below the horizon. During the daytime, the sun sits over the blue part of the background and at night it sits over the black. During dawn or dusk, the mechanical sun is positioned over the red part of the background.
Written on the eastern (left) part of the horizon is aurora (dawn in Latin) and ortus (rising). On the western (right) part is occasus (sunset), and crepusculum (twilight).
Golden Roman numbers at the outer edge of blue circle are the timescale of a normal 24 hour day and indicate time in local Prague time, or Central European Time. Curved golden lines dividing the blue part of dial into 12 parts are marks for unequal hours. These hours are defined as 1/12 of the time between sunrise and sunset, and vary as the days grow longer or shorter during the year.
Zodiacal ring

Astronomical dial
Inside the large black outer circle lies another movable circle marked with the signs of the zodiac which indicates the location of the sun on...(and so on)

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Megahertz myth

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(Redirected from Megahertz Myth)
The megahertz myth, or less commonly the gigahertz myth, refers to the error of 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 pipelines and instruction sets can greatly affect the performance when considering different processors. For example, one processor may take one clock cycle to add two numbers and another clock cycle to multiply by a third number, whereas another processor may do the same calculation in one clock cycle. Comparisons between different types of processors are difficult because performance varies depending on the type of task.
A benchmark is a better way of measuring and comparing computer performance.
Contents
1 Basis of the myth
2 Historical development
2.1 Background
2.2 Rise of the myth
2.3 The myth becomes counterproductive
3 References
4 External links
//
Basis of the myth
The myth arose because the clock speed 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 widespread use (or was even originally coined) in the context of comparing PowerPC-based Apple Macintosh computers with Intel-based PCs. Marketing based on the myth led to the clock speed being given higher priority than actual performance, and led to AMD introducing model numbers giving a notional clock speed based on comparative performance to overcome a perceived deficiency in their actual clock speed.
For example, a processor at twice the clock speed may only accomplish half the number of instructions per cycle, thereby offering no more performance than the slower-clocked alternative.
Historical development
Background
The x86 CISC 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 Mac computers using these PPC CPUs, but IBM's intention to produce its own desktop computers using these chips was thwarted by delays in Windows NT and a falling out with Microsoft. Initially this architecture met hopes for performance, and different ranges of PPC CPUs were developed, often delivering different performances at the same clock speed. 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 speed.
Rise of the myth
Computer advertising emphasised processor megahertz, and by late 1997 rapidly increasing clock speeds enabled the Pentium II to surpass the PowerPC in performance. Apple then introduced Macs using the PowerPC G3 which they claimed outperformed Pentium IIs while consuming less power. They illustrated this with commercials showing a Pentium II on a snail, and a "Toasted Bunny"-suited character parodying Intel's commercials. Intel continued to promote their higher clock speed, 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.
In November 2000 Intel's heavily advertised advances in clock speed reached an extreme with the release of the Pentium 4 which sacrificed per-cycle performance and used a deep instruction pipeline to gain higher clock speeds, ignoring problems that this introduced heat production and power consumption.
Comparisions 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 867MHzG4 as completing a task in 45seconds while a 1.7GHzPentium4 took 82seconds 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 speed.
AMD also produced x86 designs which competed with Intel on performance rather than price. In January 2002 the Pentium 4 gained a lead in sales and AMD marketing responded by giving their processors numeric suffixes approximating the clock rate that an AMD Thunderbird (and by inference a Pentium processor) would need to give matching performance, openly undermining the "megahertz myth".
The myth becomes counterproductive
The Pentium 4 was unsuitable for laptops due to its heat dissipation and power requirements, and in March 2003 Intel overcame these difficulties with the Pentium M, which proved capable of matching the Pentium 4 on performance at significantly lower clock rates. In...(and so on)

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