de_dust2_snow

 

Download this map   –   click here

 

Early computing machines had fixed programs. For example, a desk calculator is a fixed program computer. It can do basic mathematics, but it can not be used as a word processor or a gaming console. Changing the application of a fixed-program machine requires re-wiring, re-structuring, or re-designing the machine. The earliest computers were not so much “programmed” as they were “designed”. “Reprogramming”, when it was possible at all, was a laborious process, starting with flowcharts and paper notes, followed by detailed engineering designs, and then the often-arduous process of physically re-wiring and re-building the machine. [78 ]

With the proposal of the stored-program computer this changed. A stored-program computer by design includes an instruction set and can store in memory a set of instructions (a program) that details the computation.
The theoretical basis for the stored-program computer had been laid by Alan Turing in his 1936 paper. In 1945 Turing joined the National Physical Laboratory and began work on developing an electronic stored-program digital computer. His 1945 report ‘Proposed Electronic Calculator’ was the first specification for such a device.

Meanwhile, John von Neumann at the Moore School of Electrical Engineering, University of Pennsylvania, circulated his First Draft of a Report on the EDVAC in 1945. Although substantially similar to Turing’s design and engineering containing comparatively little detail, the computer architecture outlined it became known as the “von Neumann architecture”. Turing presented a more detailed paper to the National Physical Laboratory (NPL) Executive Committee in 1946, giving the first reasonably complete design of a stored-program computer, a device he called the Automatic Computing Engine (ACE). However, the better-known EDVAC design of John von Neumann, who knew of Turing’s theoretical work, received more publicity, despite its incomplete nature and questionable lack of attribution of the sources of some of the ideas. [43]

Turing felt that speed and size of memory were crucial and he proposed a high-speed memory of what would today be called 25 KB, accessed at a speed of 1 MHz. The ACE implemented subroutine calls, whereas the EDVAC did not, and the ACE also used Abbreviated Computer Instructions, an early form of programming language.

The Manchester Small-Scale Experimental Machine, nicknamed Baby, was the world’s first stored-program computer. It was built at the Victoria University of Manchester by Frederic C. Williams, Tom Kilburn and Geoff Tootill, and ran its first program on 21 June 1948. [79]

The machine was not intended to be a practical computer but was instead designed as a testbed for the Williams tube, the first random-access digital storage device. [80] Invented by Freddie Williams and Tom Kilburn [81] [82] at the University of Manchester in 1946 and 1947, it was a cathode ray tube that used an effect called secondary emission to temporarily store electronic binary data, and was used successfully in several early computers.

Although the computer was considered “small and primitive” by the standards of its time, it was the first working machine to contain all of the elements essential to a modern electronic computer. [83] As soon as the SSEM had demonstrated the feasibility of its design, a project was initiated at the university to develop it into a more usable computer, the Manchester Mark 1. John Mark 1 in turn quickly became the prototype for the Ferranti Mark 1, the the world’s first commercially available general-purpose computer. [84]

The SSEM had a 32-bit word length and a memory of 32 words. As it was designed to be the simplest possible stored-program computer, the only arithmetic operations implemented in hardware were subtraction and negation; other arithmetic operations were implemented in software. The first of three programs written for the machine found the highest proper divisor of 218 (262,144), a calculation that was known would take a long time to run-and they prove the computer’s reliability-by testing every integer from 218-1 downwards, as division was implemented by repeated subtraction of the divisor. The program consisted of 17 instructions and ran for 52 minutes before reaching the correct answer of 131,072, after the SSEM had performed 3.5 million operations (for an effective CPU speed of 1.1 kips).

The experimental machine he led to the development of the Manchester Mark 1 at the University of Manchester. [85] Work began in August 1948, and the first version was operational by April 1949; a program written to search for Mersenne primes ran error-free for nine hours on the night of 16/17 June 1949. The machine’s successful operation was widely reported in the British press, which used the phrase “electronic brain” and describing it to their readers.

The computer is especially historically significant because of its pioneering inclusion of index registers, an innovation which made it easier for the program to read sequentially through an array of words in memory. Thirty-four patents resulted from the machine’s development, and many of the ideas behind its design were incorporated in subsequent commercial products such as the IBM 701 and 702 as well as the Ferranti Mark first the chief designers, Frederic C. Williams and Tom Kilburn , concluded from their experiences with the Mark 1 that computers would be used more in scientific roles than in pure mathematics. In 1951 they started development work on Meg, the Mark 1’s successor, which would include a floating point unit.

Mercury’s surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. Because knowledge of Mercury’s geology had been based only on the 1975 Mariner 10 flyby and terrestrial observations, it is the least understood of the terrestrial planets.[23] As data from MESSENGER orbiter are processed, this knowledge will increase. For example, an unusual crater with radiating troughs has been discovered that scientists called “the spider”.[34] It was later named Apollodorus
Names for features on Mercury come from a variety of sources. Names coming from people are limited to the deceased. Craters are named for artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field. Ridges, or dorsa, are named for scientists who have contributed to the study of Mercury. Depressions or fossae are named for works of architecture. Montes are named for the word “hot” in a variety of languages. Plains or planitiae are named for Mercury in various languages. Escarpments or rupēs are named for ships of scientific expeditions. Valleys or valles are named for radio telescope facilities.[38]

Mercury was heavily bombarded by comets and asteroids during and shortly following its formation 4.6 billion years ago, as well as during a possibly separate subsequent episode called the Late Heavy Bombardment that ended 3.8 billion years ago.[39] During this period of intense crater formation, Mercury received impacts over its entire surface,[37] facilitated by the lack of any atmosphere to slow impactors down.[40] During this time Mercury was volcanically active; basins such as the Caloris Basin were filled by magma, producing smooth plains similar to the maria found on the Moon.[41][42]

Data from the October 2008 flyby of MESSENGER gave researchers a greater appreciation for the jumbled nature of Mercury’s surface. Mercury’s surface is more heterogeneous than either Mars’s or the Moon’s, both of which contain significant stretches of similar geology, such as maria and plateaus.
Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that the area blanketed by their ejecta is much smaller, a consequence of Mercury’s stronger surface gravity.[44] According to IAU rules, each new crater must be named after an artist that was famous for more than fifty years, and dead for more than three years, before the date the crater is named
The largest known crater is Caloris Basin, with a diameter of 1,550 km.[46] The impact that created the Caloris Basin was so powerful that it caused lava eruptions and left a concentric ring over 2 km tall surrounding the impact crater. At the antipode of the Caloris Basin is a large region of unusual, hilly terrain known as the “Weird Terrain”. One hypothesis for its origin is that shock waves generated during the Caloris impact traveled around Mercury, converging at the basin’s antipode (180 degrees away). The resulting high stresses fractured the surface.[47] Alternatively, it has been suggested that this terrain formed as a result of the convergence of ejecta at this basin’s antipode.[48]

Overall, about 15 impact basins have been identified on the imaged part of Mercury. A notable basin is the 400 km wide, multi-ring Tolstoj Basin that has an ejecta blanket extending up to 500 km from its rim and a floor that has been filled by smooth plains materials. Beethoven Basin has a similar-sized ejecta blanket and a 625 km diameter rim.[44] Like the Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts.