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Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, they give off less heat. Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. Transistors greatly reduced computers’ size, initial cost, and operating cost. Typically, second-generation computers were composed of large numbers of printed circuit boards such as the IBM Standard Modular System [108] each carrying one to four logic gates or flip-flops.

At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of valves. Initially the only devices available were germanium point-contact transistors, less reliable than the valves they replaced but which consumed far less power. [109] Their first transistorised computer and the first in the world, was operational by 1953, [110] and a second version was completed there in April 1955. [111] The 1955 version used 200 transistors, 1,300 solid-state diodes and had a power consumption of 150 watts. However, the machine did make use of valves to generate its 125 kHz clock waveforms and in the circuitry to read and write on its magnetic drum memory, as it was not the first completely transistorized computer.

That distinction goes to the Harwell CADET of 1955, [112] built by the electronics division of the Atomic Energy Research Establishment at Harwell. The design featured a 64-kilobyte magnetic drum memory store with multiple moving heads that had been designed at the National Physical Laboratory, UK. By 1953 this team had transistor circuits operating to read and write on a smaller magnetic drum from the Royal Radar Establishment. The machine used a low clock speed of only 58 kHz to avoid having to use any valves to generate the clock waveforms. [113] [114]

CADET used 324 point-contact transistors provided by the UK company Standard Telephones and Cables; 76 junction transistors were used for the first stage amplifiers for data read from the drum, since point-contact transistors were too noisy. From August 1956 CADET was offering a regular computing service, during which it often executed continuous computing runs of 80 hours or more. [115] [116] Problems with the reliability of early batches of point contact and alloyed junction transistors meant that the machine’s mean time between failures was about 90 minutes, but this improved once the more reliable bipolar junction transistors became available. [117]

The Transistor Computer’s design was adopted by the local engineering firm of Metropolitan-Vickers and their Metrovick 950, the first commercial transistor computer anywhere. [118] Six Metrovick 950S were built, the first completed in 1956. They were successfully deployed within various departments of the company and were in use for about five years. [111]

A second generation computer, the IBM 1401, captured about one third of the world market. IBM installed more than ten thousand 1401s between 1960 and in 1964.

Transistorized electronics improved not only the CPU (Central Processing Unit), but also the peripheral devices. The second generation disk data storage units were able to store tens of millions of letters and digits. Next to the fixed disk storage units, connected to the CPU via high-speed data transmission, were removable disk data storage units. A removable disk pack can be easily exchanged with another pack in a few seconds. Even if the removable disks’ capacity is smaller than fixed disks, their interchangeability guarantees a nearly unlimited quantity of data close at hand. Magnetic tape provided archival capability for this data, at a lower cost than disk.

Many second-generation CPUs delegated peripheral device communications to a secondary processor. For example, while the communication processor controlled card reading and punching, the main CPU executed calculations and binary branch instructions. One databus would bear data between the main CPU and core memory at the CPU’s fetch-execute cycle rate, and other databusses would typically serve the peripheral devices. On the PDP-1, the core memory’s cycle time was 5 microseconds; consequently most arithmetic instructions took 10 microseconds (100,000 operations per second) because most operations took at least two memory cycles; one for the instruction, one for the operand data fetch.

During the second generation remote terminal units (often in the form of teleprinters like a Friden Flexowriter) saw greatly increased use. [119] Telephone connections provided sufficient speed for early remote terminals and allowed hundreds of kilometers separation between remote-terminals and the computing center. Eventually these stand-alone computer networks would be generalized into an interconnected network of networks-the Internet

The early 1960s saw the advent of supercomputing. The Atlas Computer was a joint development between the University of Manchester, Ferranti, and Plessey, and was first installed at Manchester University and officially commissioned in 1962 as one of the world’s first supercomputers – considered to be the most powerful computer in the world at that time. [121] It was said that whenever Atlas went offline half of the United Kingdom’s computer capacity was lost. [122] It was a second-generation machine, using discrete germanium transistors. Atlas also pioneered the Atlas Supervisor, “considered by many to be the first recognisable modern operating system”. [123]

In the US, a series of computers at Control Data Corporation (CDC) were designed by Seymour Cray to use innovative designs and parallelism to achieve superior computational peak performance. [124] The CDC 6600, released in 1964, is generally considered the first supercomputer. [125] [126] The CDC 6600 outperformed its predecessor, the IBM 7030 Stretch, by about a factor of three. With performance of about 1 Megaflops, the CDC 6600 was the world’s fastest computer from 1964 to 1969, when it relinquished that status to its successor, the CDC 7600th

The next great advance in computing power came with the advent of the integrated circuit. The idea of the integrated circuit was conceived by a radar scientist working for the Royal Radar Establishment of the Ministry of Defence, Geoffrey W. A. Dummer. Dummer presented the first public description of an integrated circuit at the Symposium on Progress in Quality Electronic Components in Washington, D.C. on 7 May 1952: [127]

With the advent of the transistor and the work on semi-conductors generally, it now seems possible to envisage electronic equipment and a solid block with no connecting wires. [128] The block may consist of layers of insulating, conducting, rectifying and amplifying materials, the electronic functions being connected directly by cutting out areas of the various layers. “

The first practical ICs were invented by Jack Kilby at Texas Instruments and Robert Noyce at Fairchild Semiconductor. [129] Kilby recorded his initial ideas concerning the integrated circuit in July 1958, successfully demonstrating the first working integrated example on 12 September 1958. [130] In his patent application of 6 February 1959, Kilby described his new device as “a body of semiconductor material … Wherein all the components of the electronic circuit are completely integrated.” [131] The first customer for the invention was the US Air Force. [132]

Noyce also came up with his own idea of an integrated circuit half a year later than Kilby. [133] His chip solved many practical problems that Kilby’s had not. Produced at Fairchild Semiconductor, it was made of silicon, whereas Kilby’s chip was made of germanium

There are two geologically distinct plains regions on Mercury.[44][50] Gently rolling, hilly plains in the regions between craters are Mercury’s oldest visible surfaces,[44] predating the heavily cratered terrain. These inter-crater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km in diameter.
Smooth plains are widespread flat areas that fill depressions of various sizes and bear a strong resemblance to the lunar maria. Notably, they fill a wide ring surrounding the Caloris Basin. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains. Despite a lack of unequivocally volcanic characteristics, the localisation and rounded, lobate shape of these plains strongly support volcanic origins.[44] All the smooth plains of Mercury formed significantly later than the Caloris basin, as evidenced by appreciably smaller crater densities than on the Caloris ejecta blanket.[44] The floor of the Caloris Basin is filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. It is not clear whether they are volcanic lavas induced by the impact, or a large sheet of impact melt.
One unusual feature of Mercury’s surface is the numerous compression folds, or rupes, that crisscross the plains. As Mercury’s interior cooled, it contracted and its surface began to deform, creating wrinkle ridges and lobate scarps associated with thrust faults. The scarps can reach lengths of 1000 km and heights of 3 km.[51] These compressional features can be seen on top of other features, such as craters and smooth plains, indicating they are more recent.[52] Mapping of the features has suggested a total shrinkage of Mercury’s radius in the range of ~1 to 7 km.[53] Small-scale thrust fault scarps have been found, tens of meters in height and with lengths in the range of a few km, that appear to be less than 50 million years old, indicating that compression of the interior and consequent surface geological activity continue to the present.
Images obtained by MESSENGER have revealed evidence for pyroclastic flows on Mercury from low-profile shield volcanoes.[54][55][56] MESSENGER data has helped identify 51 pyroclastic deposits on the surface,[57] where 90% of them are found within impact craters.[57] A study of the degradation state of the impact craters that host pyroclastic deposits suggests that pyroclastic activity occurred on Mercury over a prolonged interval.[57]

A “rimless depression” inside the southwest rim of the Caloris Basin consists of at least nine overlapping volcanic vents, each individually up to 8 km in diameter. It is thus a “compound volcano”.[58] The vent floors are at a least 1 km below their brinks and they bear a closer resemblance to volcanic craters sculpted by explosive eruptions or modified by collapse into void spaces created by magma withdrawal back down into a conduit.[58] The scientists could not quantify the age of the volcanic complex system, but reported that it could be of the order of a billion years.
The surface temperature of Mercury ranges from 100 K to 700 K[60] at the most extreme places: 0°N, 0°W, or 180°W. It never rises above 180 K at the poles,[10] due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. The subsolar point reaches about 700 K during perihelion (0°W or 180°W), but only 550 K at aphelion (90° or 270°W).[61] On the dark side of the planet, temperatures average 110 K.[10][62] The intensity of sunlight on Mercury’s surface ranges between 4.59 and 10.61 times the solar constant (1,370 W·m−2).[63]

Although the daylight temperature at the surface of Mercury is generally extremely high, observations strongly suggest that ice (frozen water) exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K; far lower than the global average.[64] Water ice strongly reflects radar, and observations by the 70-meter Goldstone Solar System Radar and the VLA in the early 1990s revealed that there are patches of high radar reflection near the poles.[65] Although ice was not the only possible cause of these reflective regions, astronomers think it was the most likely.[66]

The icy regions are estimated to contain about 1014–1015 kg of ice,[67] and may be covered by a layer of regolith that inhibits sublimation.[68] By comparison, the Antarctic ice sheet on Earth has a mass of about 4×1018 kg, and Mars’s south polar cap contains about 1016 kg of water.[67] The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by impacts of comets.[67]

Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have a tenuous surface-bounded exosphere[69] containing hydrogen, helium, oxygen, sodium, calcium, potassium and others at a surface pressure of less than approximately 0.5 nPa (0.005 picobars).[13] This exosphere is not stable—atoms are continuously lost and replenished from a variety of sources. Hydrogen atoms and helium atoms probably come from the solar wind, diffusing into Mercury’s magnetosphere before later escaping back into space. Radioactive decay of elements within Mercury’s crust is another source of helium, as well as sodium and potassium. MESSENGER found high proportions of calcium, helium, hydroxide, magnesium, oxygen, potassium, silicon and sodium. Water vapor is present, released by a combination of processes such as: comets striking its surface, sputtering creating water out of hydrogen from the solar wind and oxygen from rock, and sublimation from reservoirs of water ice in the permanently shadowed polar craters. The detection of high amounts of water-related ions like O+, OH−, and H2O+ was a surprise. Because of the quantities of these ions that were detected in Mercury’s space environment, scientists surmise that these molecules were blasted from the surface or exosphere by the solar wind.

Sodium, potassium and calcium were discovered in the atmosphere during the 1980–1990s, and are thought to result primarily from the vaporization of surface rock struck by micrometeorite impacts[74] including presently from Comet Encke.[75] In 2008, magnesium was discovered by MESSENGER.[76] Studies indicate that, at times, sodium emissions are localized at points that correspond to the planet’s magnetic poles. This would indicate an interaction between the magnetosphere and the planet’s surface.

On November 29, 2012, NASA confirmed that images from MESSENGER had detected that craters at the north pole contained water ice. MESSENGER’s principal investigator Sean Solomon is quoted in the New York Times estimating the volume of the ice to be large enough to “encase Washington, D.C., in a frozen block two and a half miles deep

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